SG2-Type R2R3-MYB Transcription Factor MYB15 Controls Defense-Induced Lignification and Basal Immunity in Arabidopsis

The LoMYB26/LoJAZ4-LoCOMT module regulates anther dehiscence via Jasmonic acid-mediated endothecium lignification in lily

INTRODUCTION

Timely anther dehiscence is a key step for successful sexual reproduction in plants. Secondary cell wall thickening of anther endothecium is a vital process during anther dehiscence that provides an indispensable mechanical force for successful dehiscence. Anther dehiscence depends on anther lignification, and it is a timely and sophisticated process regulated by phytohormones and transcription factors. However, whether endothecium lignification occurs during anther dehiscence in lily and underlying mechanisms are still largely unclear.

OBJECTIVES

Our work focuses on identifying the course of endothecium lignification during anther dehiscence and elucidating the molecular mechanisms underlying endothecium lignification-dependent anther dehiscence in lily.

METHODS

Lignin fluorescence analysis and ultraviolet spectrophotometry were employed to elucidate the endothecium lignification process. Target genes were isolated from the transcriptomic data of anther dehiscence and lignification process. Virus-induced gene silencing (VIGS) and transient overexpression in lily anthers were used to analyze the LoMYB26 function. Yeast one-hybrid (Y1H), electrophoretic mobility shift assay (EMSA), and dual-luciferase (LUC) assay analyzed the regulatory mechanisms. Yeast two-hybrid (Y2H), luciferase complementation imaging (LCI), and bimolecular fluorescence complementation (BiFC) assays illustrated the interaction between LoMYB26 and LoJAZ4.

RESULTS

Our results showed that endothecium lignification occurred in S6-S7 stages when anther dehiscence had not yet occurred. The R2R3-type MYB transcription factor, LoMYB26, was found to promote endothecium lignification. LoMYB26 directly bound to the Caffeic Acid O-methyltransferase (LoCOMT) promoter and activated its transcription. Meanwhile, LoMYB26 interacted with jasmonate-ZIM domain protein 4 (LoJAZ4), which repressed the LoMYB26-mediated activation of LoCOMT transcription. Additionally, the exogenous application of methyl-jasmonate (Me-JA) induced LoMYB26 transcription and promoted endothecium lignification.

CONCLUSION

Our findings demonstrate that LoMYB26 promotes endothecium lignification and anther dehiscence. LoMYB26 interacted with LoJAZ4, forming a heterodimer that participates in JA-mediated endothecium lignification and anther dehiscence. This study offers valuable insights and a theoretical foundation for the breeding of anther-indehiscent lily.

The MYB transcription factor TaMYB30 enhances wheat resistance to sharp eyespot disease by scavenging ROS accumulation

Sharp eyespot disease, caused primarily by the necrotrophic fungal pathogen Rhizoctonia cerealis, poses a significant threat to global wheat production. This study reports the functional characterization of an R2R3-MYB transcription factor, TaMYB30, which plays a crucial role in wheat's resistance to R. cerealis. The overexpression of TaMYB30 in transgenic wheat led to enhanced resistance against sharp eyespot disease, whereas its knockdown in wheat notably compromised resistance, indicating that TaMYB30 acts as a positive regulator in wheat's defense against R. cerealis infection. Comparative transcriptomic analysis between transgenic and wild-type wheat following R. cerealis infection revealed that differentially expressed genes were primarily involved in oxidative stress response, peroxidase activity, and glutathione metabolism. Further functional analysis demonstrated that TaMYB30 directly activates the expression of PRX and GST genes. Transgenic wheat with elevated TaMYB30 expression also exhibited significantly enhanced tolerance to oxidative stress compared to wild-type plants. Notably, overexpression of TaMYB30 mitigated hydrogen peroxide (H2O2) accumulation post-infection, suggesting that the resistance conferred by TaMYB30 is likely due to its role in scavenging reactive oxygen species (ROS) accumulation. This research uncovers a novel regulatory function for MYB transcription factors in wheat defense mechanisms and proposes TaMYB30 as a promising candidate for genetic improvement to enhance wheat's resistance to sharp eyespot and oxidative stress.

Integrated metabolomic and transcriptomic analysis of the anthocyanin regulatory networks in Lagerstroemia indica petals

BACKGROUND

Lagerstroemia indica is an ornamental plant with high economic and ecological values. However, the mechanism underlying the regulation of L. indica petal color variation remains unclear. We used LC-MS/MS and RNA-seq to uncover the genetic basis of flower colour variation with the help of the metabolome and transcriptome of three varieties with different colored petal, 'Huahai', 'Zhuimeng', 'Zixian'.

RESULTS

A total of 54 anthocyanidins were identified, 11 peonidin derivatives, 10 cyanidin derivatives, 9 delphinidin derivatives, 5 petunidin derivatives, 5 malvidin derivatives, 4 pelargonidin derivatives, 2 procyanidin derivatives, and 8 other flavonoids. Delphinidin-3-O-glucoside, Malvidin-3-O-glucoside, Petunidin-3-O-glucoside were abundant in petals of all three varieties. 28 differentially accumulated metabolites, including peonidin, cyanidins and flavonoids, were common to 'Zixian' vs. 'Huahai' and 'Zhuimeng' vs. 'Huahai'. Malvidin-3-O-glucoside, Peonidin-3-O-glucoside varied greatly among three varieties. A total of 9923 genes were found to be differentially expressed between red and other colored petals. The upregulation of the expression of ANS (LOC116213234), CHI (LOC116194939), CHI (LOC116196656), F3H (LOC116211316), F3'H (LOC116198721), UGT (LOC104445830) and UGT (LOC116210262) in 'Huahai' was consistent with the contents of cyanidin derivatives, delphinidin derivatives, kaempferol derivatives, naringenin, peonidin derivatives and petunidin derivatives. Regarding transcription factors associated with the anthocyanin pthway, the MYB gene family had the highest number of DEGs, followed by the bHLH gene family, bZIP gene family, WRKY gene family, and MADS box gene family.

CONCLUSION

Malvidin-3-O-glucoside and Peonidin-3-O-glucoside may contribute to variation of petal color in the three varieties. The upregulation of ANS, CHI, F3H, F3'H and UGT expression is involved in anthocyanin biosynthesis of the red pigmentation in the L. indica variety. Expression of twelve transcription factor genes has a strongly positive correlation with expression of structural genes. Collectively, our results may facilitate the genetic breeding and cultivation of L. indica with enhanced red pigmentation.

Diverse roles of MYB transcription factors in plants

MYB transcription factors (TFs), one of the largest TF families in plants, are involved in various plant-specific processes as the central regulators, such as in phenylpropanoid metabolism, cell cycle, formation of root hair and trichome, phytohormones responses, reproductive growth and abiotic or biotic stress responses. Here we summarized multiple roles and explained the molecular mechanisms of MYB TFs in plant development and stress adaptation. The exploration of MYB TFs contributes to a better comprehension of molecular regulation in plant development and environmental adaptability.

PcMYB44 regulated host resistance to Botryosphaeria dothidea through activation of lignin biosynthesis and disease-resistance gene expression in pear

Pear ring rot disease, the pathogen of Botryosphaeria dothidea causes significant threat to the healthy development of the pear industry, therefore the exploration of disease-resistant gene resources is crucial for disease prevention and control. Members of the R2R3-MYB subfamily play important roles in regulating pathogen resistance in plants, however the gene function in regulating host resistance in pear remains unclear. In this study, the role of PcMYB44 were investigated in regulating host resistance disease in pear calli using both forward and reverse genetic approaches. Overexpression of PcMYB44 positively regulates the disease resistance, whereas knockout of PcMYB44 results in a phenotype with decreased resistance. Our results further demonstrated that PcMYB44 could directly affect lignin content and resistance to fungal diseases by regulating the PcmiR397-PcLACs module and lignin biosynthesis gene expression levels. Additionally, overexpressing PcMYB44 also elevated expression levels of key genes of JA/SA/ET pathway. The obtained results revealed that PcMYB44 regulated host resistance to ring rot disease through synergistic regulation the lignification and activating disease-resistance gene expression of JA/SA/ET defense pathways as a underlying secondary mechanism, which provide valuable genetic resources for molecular breeding for disease resistance.

LACCASE35 enhances lignification and resistance against Pseudomonas syringae pv. actinidiae infection in kiwifruit

Kiwifruit bacterial canker, a highly destructive disease caused by Pseudomonas syringae pv. actinidiae (Psa), seriously affects kiwifruit (Actinidia spp.) production. Lignin deposition in infected cells serves as a defense mechanism, effectively suppressing pathogen growth. However, the underlying process remains unclear. In this study, we determined that Psa infection leads to a significant increase in S-lignin accumulation in kiwifruit. The S/G ratio in lignin was higher in a Psa-resistant cultivar than in a Psa-sensitive cultivar. Furthermore, kiwifruit laccase 35 (AcLac35), encoding an enzyme in the lignin biosynthesis pathway with characteristic laccase activity, showed tissue-specific expression in plants and was upregulated following infection by Psa. Overexpressing AcLac35 in kiwifruit leaves resulted in greater lignin content than in wild-type leaves, leading to the formation of thicker cell walls, and also activated plant-pathogen interactions and MAPK pathways, thereby enhancing resistance against Psa infection. Yeast 1-hybrid assays, dual-LUC reporter assays, electrophoretic mobility shift assays, and transient injection experiments indicated that SQUAMOSA PROMOTER-BINDING PROTEIN-LIKE 9 (AcSPL9) can bind to the AcLac35 promoter, thereby positively regulating its expression. Moreover, overexpression of AcSPL9 increased lignin accumulation in kiwifruit leaves, enhancing resistance to Psa, while virus-induced gene silencing of AcSPL9 expression reduced this resistance. Our findings reveal the function of AsSPL9-AcLac35 in kiwifruit, providing insight into enhancing resistance against Psa in kiwifruit.

PbrMYB14 Enhances Pear Resistance to Alternaria alternata by Regulating Genes in Lignin and Salicylic Acid Biosynthesis Pathways

Pear is an important originate fruiter in China, ranking first in the world in terms of cultivation area and yield. However, it is susceptible to infection by Alternaria alternata (A. alternata), resulting in a reduction of approximately 30% in yield. While both lignin and salicylic acid (SA) are recognized as key components of plant immune responses, the molecular mechanisms connecting these pathways remain poorly understood. Here, we have discovered a nuclear localization transcription activator PbrMYB14 in pears, whose expression can be induced by exogenous SA and A. alternata. Overexpression of PbrMYB14 significantly increased lignin and SA content in pears, making them more resistant to A. alternata, and the relative lesion area decreased by 68.95% compared with WT plants. By analyzing the transcriptome of PbrMYB14-overexpressing plants, the lignin synthesis gene Pbr4CL1 and SA synthesis gene PbrPAL1 regulated by PbrMYB14 were screened and identified. Through yeast one-hybrid (Y1H) and a Dual-Luciferase assay (LUC), it was confirmed that PbrMYB14 positively regulates the expression of Pbr4CL1 and PbrPAL1 genes. Our results suggest that PbrMYB14 links lignin resistance and SA resistance in pears, providing valuable information for future genetic breeding research on pear disease resistance.

Lignin Metabolism Is Crucial in the Plant Responses to Tambocerus elongatus (Shen) in Camellia sinensis L

Tambocerus elongatus (Shen) (Hemiptera: Cicadellidae) is a devastating insect pest species of Camellia sinensis, significantly affecting the yield and quality of tea. Due to growing concerns over the irrational use of insecticides and associated food safety, it is crucial to better understand the innate resistance mechanism of tea trees to T. elongatus. This study aims to explore the responses of tea trees to different levels of T. elongatus infestation. We first focused on the primary metabolism and found that the amino acid levels decreased significantly with increasing T. elongatus infestation, while sugar accumulation showed an opposite trend. Moreover, secondary metabolite analysis showed a significant increase in flavonoid compounds and lignin content after T. elongatus infestation. Metabolomics analysis of the flavonoid compounds revealed a decrease in the proanthocyanidin level and an increase in anthocyanidin glycosides (anthocyanins and their derivatives) after T. elongatus infestation. T. elongatus infestation also caused a decrease in the abundance of non-ester catechins and an increase in the abundance of ester catechins. Furthermore, the gene expression analysis revealed that transcripts of genes involved in flavonoid biosynthesis, such as CsCHI, CsF3H, CsF3'H, CsFNS, CsFLS, and CsUFGT, were down-regulated, while genes involved in the lignin pathway were up-regulated by insect infestation, suggesting that lignin probably plays a pivotal role in tea plant response to T. elongatus infestation. Analysis of the expression of related genes indicates that the jasmonate (JA) pathway primarily responds to leafhopper damage. These findings suggest that the lignin pathway and JA play a preferential role in tea plant response to T. elongatus. Furthermore, the production of saccharides and the accumulation of anthocyanin glycosides in the flavonoid metabolic pathway are critical during this stress response. Further exploration of the roles of anthocyanin glycosides and lignin in tea tree resistance could provide a theoretical basis for understanding the defense mechanism of tea trees against T. elongatus damage.

Harnessing Genetic Resistance in Maize and Integrated Rust Management Strategies to Combat Southern Corn Rust

Southern corn rust (SCR) caused by Puccinia polysora Underw. has recently emerged as a focal point of study because of its extensive distribution, significant damage, and high prevalence in maize growing areas such as the United States, Canada, and China. P. polysora is an obligate biotrophic fungal pathogen that cannot be cultured in vitro or genetically modified, thus complicating the study of the molecular bases of its pathogenicity. High temperatures and humid environmental conditions favor SCR development. In severe cases, SCR may inhibit photosynthesis and cause early desiccation of maize, a decrease in kernel weight, and yield loss. Consequently, an expedited and accurate detection approach for SCR is essential for plant protection and disease management. Significant progress has been made in elucidating the pathogenic mechanisms of P. polysora, identifying resistance genes and developing SCR-resistant cultivars. A detailed understanding of the molecular interactions between maize and P. polysora will facilitate the development of novel and effective approaches for controlling SCR. This review gives a concise overview of the biological characteristics and symptoms of SCR, its life cycle, the molecular basis of interactions between maize and P. polysora, the genetic resistance of maize to SCR, the network of maize resistance to P. polysora infection, SCR management, and future perspectives.

The MdERF61-mdm-miR397b-MdLAC7b module regulates apple resistance to Fusarium solani via lignin biosynthesis

Apple replant disease (ARD) is a worldwide problem that threatens the industry. However, the genetic mechanism underlying plant disease resistance against ARD remains unclear. In this study, a negative regulatory microRNA in Malus domestica, mdm-miR397b, and its direct target MdLAC7b (Laccase) was selected for examination based on our previous small RNA and degradome sequencing results. Overexpressing the mdm-miR397b-MdLAC7b module altered the lignin deposition and jasmonic acid contents in apple roots, which also led to increased resistance to Fusarium solani. Additionally, Y1H library screening using mdm-miR397b promoter recombinants identified a transcription factor, MdERF61, that represses mdm-miR397b transcriptional activity by directly binding to 2 GCC-boxes in the mdm-miR397b promoter. In summary, our results suggest that the MdERF61-mdm-miR397b-MdLAC7b module plays a crucial role in apple resistance to F. solani and offers insights for enhancing plant resistance to soil-borne diseases in apples.

The FERONIA-RESPONSIVE TO DESICCATION 26 module regulates vascular immunity to Ralstonia solanacearum

Some pathogens colonize plant leaves, but others invade the roots, including the vasculature, causing severe disease symptoms. Plant innate immunity has been extensively studied in leaf pathosystems; however, the precise regulation of immunity against vascular pathogens remains largely unexplored. We previously demonstrated that loss of function of the receptor kinase FERONIA (FER) increases plant resistance to the typical vascular bacterial pathogen Ralstonia solanacearum. Here, we show that upon infection with R. solanacearum, root xylem cell walls in Arabidopsis thaliana become highly lignified. FER is specifically upregulated in the root xylem in response to R. solanacearum infection, and inhibits lignin biosynthesis and resistance to this pathogen. We determined that FER interacts with and phosphorylates the transcription factor RESPONSIVE TO DESICCATION 26 (RD26), leading to its degradation. Overexpression and knockout of RD26 demonstrated that it positively regulates plant resistance to R. solanacearum by directly activating the expression of lignin-related genes. Tissue-specific expression of RD26 in the root xylem confirmed its role in vascular immunity. We confirmed that the FER-RD26 module regulates lignin biosynthesis and resistance against R. solanacearum in tomato (Solanum lycopersicum). Taken together, our findings unveil that the FER-RD26 cascade governs plant immunity against R. solanacearum in vascular tissues by regulating lignin deposition. This cascade may represent a key defense mechanism against vascular pathogens in plants.

MYB168 and WRKY20 transcription factors synergistically regulate lignin monomer synthesis during potato tuber wound healing

Lignin is a critical component of the closing layer of the potato (Solanum tuberosum L.) tuber during healing; however, the molecular mechanism of its formation remains poorly understood. To elucidate the molecular mechanism of tuber healing, we screened the genes encoding transcription factors that regulate lignin synthesis(StMYB24/49/105/144/168, StWRKY19/20/22/23/34) and the key genes involved in lignin monomer synthesis (PHENYLALANINE AMMONIA LYASE 5 (StPAL5) and CINNAMYL ALCOHOL DEHYDROGENASE 14 (StCAD14)) for induced expression after wounding using transcriptome data. Dual-luciferase assay, yeast one-hybrid, electrophoretic mobility shift assay, and chromatin immunoprecipitation-qPCR assays revealed that StMYB168 could bind directly to the StPAL5 and StCAD14 promoters to activate their expression and that StWRKY20 enhanced this regulation with a synergistic effect. Y2H, bimolecular fluorophore complementation, and coimmunoprecipitation assays showed that StMYB168 interacted with StWRKY20 to form a MYB-WRKY complex. Furthermore, transient overexpression (OE) of StMYB168 and StWRKY20 in Nicotiana benthamiana leaves upregulated the expression of NbPAL and NbCAD10 and promoted lignin accumulation in the leaves. In addition, OE of StWRKY20 and StMYB168 together resulted in higher expression levels of NbPAL and NbCAD10 and higher levels of lignin monomer and total lignin. In contrast, silencing of StMYB168 and StWRKY20 in potato significantly reduced the lignin content of wounded tubers. In conclusion, StMYB168 and StWRKY20 are important regulators of lignin biosynthesis in potato tubers during healing and can positively regulate lignin biosynthesis by forming a complex. The elucidation of this regulatory module provides information on the regulatory mechanism of lignin monomer synthesis in wounded tubers at the transcriptional level.

Multi-omics analysis reveals genetic architecture and local adaptation of coumarins metabolites in Populus

BACKGROUND

Accumulation of coumarins plays key roles in response to immune and abiotic stress in plants, but the genetic adaptation basis of controlling coumarins in perennial woody plants remain unclear.

RESULTS

We detected 792 SNPs within 334 genes that were significantly associated with the phenotypic variations of 15 single-metabolic traits and multiple comprehensive index, such as principal components (PCs) of coumarins metabolites. Expression quantitative trait locus mapping uncovered that 337 eQTLs associated with the expression levels of 132 associated genes. Selective sweep revealed 55 candidate genes have potential selective signature among three geographical populations, highlighting that the coumarins biosynthesis have been encountered forceful local adaptation. Furthermore, we constructed a genetic network of seven candidate genes that coordinately regulate coumarins biosynthesis, revealing the multiple regulatory patterns affecting coumarins accumulation in Populus tomentosa. Validation of candidate gene variations in a drought-tolerated population and DUF538 heterologous transformation experiments verified the function of candidate genes and their roles in adapting to the different geographical conditions in poplar.

CONCLUSIONS

Our study uncovered the genetic regulation of the coumarins metabolic biosynthesis of Populus, and offered potential clues for drought-tolerance evaluation and regional improvement in woody plants.

Lemon zinc finger protein ClSUP induces accumulation of reactive oxygen species and inhibits citrus yellow vein-clearing virus infection via interactions with ClDOF3.4

Citrus yellow vein-clearing virus (Potexvirus citriflavivenae; CYVCV) is an increasing threat to citrus cultivation. Notably, the role of zinc finger proteins (ZFPs) in mediating viral resistance in citrus plants is unclear. In this study, we demonstrated that ZFPs ClSUP and ClDOF3.4 enhanced citrus defense responses against CYVCV in Eureka lemon (Citrus limon 'Eureka'). ClSUP interacted with the coat protein (CP) of CYVCV to reduce CP accumulation and inhibited its silencing suppressor function. Overexpression of CISUP triggered reactive oxygen species (ROS) and salicylic acid (SA) pathways, and enhanced resistance to CYVCV infection. In contrast, ClSUP silencing resulted in increased CP accumulation and down-regulated ROS and SA-related genes. ClDOF3.4 interacted with ClSUP to facilitate its interactions with CP. Furthermore, ClDOF3.4 synergistically regulated the accumulation of ROS and SA with ClSUP and accelerated down-regulation of CP accumulation. Transgenic plants co-expressing ClSUP and ClDOF3.4 significantly decreased the CYVCV. These findings provide a new reference for understanding the interaction mechanism between the host and CYVCV.

Genome-wide investigation of MYB gene family in Areca catechu and potential roles of AcTDF in transgenic Arabidopsis

BACKGROUND

MYB protein, a crucial transcription factor, holds crucial importance in plant growth, development, stress responses, and secondary metabolite regulation. While MYB proteins have been extensively studied, research on MYBs within the palm family, particularly in Areca catechu, remains limited.

METHODS AND RESULTS

This study identified 259 MYB genes in Areca catechu, including 105 1R-MYBs, 150 R2R3-MYBs, 3 3R-MYBs, and 1 4R-MYBs. Physicochemical properties, collinearity, and gene structure of these genes were analyzed. The AcMYB is distributed across 16 chromosomes of A.catechu and has 119 and 195 homologs in Arabidopsis and rice, respectively. Cis-acting elements in the promoter region suggest roles in plant hormones, growth, development, and stress. R2R3-MYB genes were divided into eight groups based on tissue expression profiles. The flowering-related gene AcTDF is highly expressed in male flowers. Overexpression of AcTDF in Arabidopsis promotes early flowering, upregulates AtSOC1 and AtFUL, and enhances tolerance to drought and salt stress.

CONCLUSIONS

These results provide valuable insights for the identification and analysis of the MYB gene family in Areca catechu and offer a basis for the subsequent verification of its related functions and the role and significance of its role in the evolution of palms.

The WRKY Family Transcription Factor GmWRKY72 Represses Glyceollin Phytoalexin Biosynthesis in Soybean

Phytoalexins are plant defense metabolites that are biosynthesized transiently in response to pathogens. Despite that their biosynthesis is highly restricted in plant tissues, the transcription factors that negatively regulate phytoalexin biosynthesis remain largely unknown. Glyceollins are isoflavonoid-derived phytoalexins that have critical roles in protecting soybean crops from the oomycete pathogen Phytophthora sojae. To identify regulators of glyceollin biosynthesis, we used a transcriptomics approach to search for transcription factors that are co-expressed with glyceollin biosynthesis in soybean and stilbene synthase phytoalexin genes in grapevine. We identified and functionally characterized the WRKY family protein GmWRKY72, which is one of four WRKY72-type transcription factors of soybean. Overexpressing and RNA interference silencing of GmWRKY72 in the soybean hairy root system decreased and increased expression of glyceollin biosynthetic genes and metabolites, respectively, in response to wall glucan elicitor from P. sojae. A translational fusion with green fluorescent protein demonstrated that GFP-GmWRKY72 localizes mainly to the nucleus of soybean cells. The GmWRKY72 protein directly interacts with several glyceollin biosynthetic gene promoters and the glyceollin transcription factor proteins GmNAC42-1 and GmMYB29A1 in yeast hybrid systems. The results show that GmWRKY72 is a negative regulator of glyceollin biosynthesis that may repress biosynthetic gene expression by interacting with transcription factor proteins and the DNA of glyceollin biosynthetic genes.

A 3R-MYB transcription factor is involved in Methyl Jasmonate-Induced disease resistance in Agaricus bisporus and has implications for disease resistance in Arabidopsis

INTRODUCTION

Methyl jasmonate (MeJA) and MYB transcription factors (TFs) play important roles in pathogen resistance in several plants, but MYB TFs in conjunction with MeJA-induced defense against Pseudomonas tolaasii in edible mushrooms remain unknown.

OBJECTIVES

To investigate the role of a novel 3R-MYB transcription factor (AbMYB11) in MeJA-induced disease resistance of Agaricus bisporus and in the resistance of transgenic Arabidopsis to P. tolaasii.

METHODS

Mushrooms were treated with MeJA alone or in combination with phenylpropanoid pathway inhibitors, and the effects of the treatments on the disease-related and physiological indicators of the mushrooms were determined to assess the role of MeJA in inducing resistance and the importance of the phenylpropanoid pathway involved. Subcellular localization, gene expression analysis, dual-luciferase reporter assay, electrophoretic mobility shift assay, and transgenic Arabidopsis experiments were performed to elucidate the molecular mechanism of AbMYB11 in regulating disease resistance.

RESULTS

MeJA application greatly improved mushroom resistance to P. tolaasii infection, and suppression of the phenylpropanoid pathway significantly weakened this effect. MeJA treatment stimulated the accumulation of phenylpropanoid metabolites, which was accompanied by increased the activities of biosynthetic enzymes and the expression of phenylpropanoid pathway-related genes (AbPAL1, Ab4CL1, AbC4H1) and an AbPR-like gene, further confirming the critical role of the phenylpropanoid pathway in MeJA-induced responses to P. tolaasii. Importantly, AbMYB11, localized in the nucleus, was rapidly induced by MeJA treatment under P. tolaasii infection; it transcriptionally activated the phenylpropanoid pathway-related and AbPR-like genes, and AbMYB11 overexpression in Arabidopsis significantly increased the transcription of phenylpropanoid-related genes, the accumulation of total phenolics and flavonoids, and improved resistance to P. tolaasii.

CONCLUSION

This study clarified the pivotal role of AbMYB11 as a regulator in disease resistance by modulating the phenylpropanoid pathway, providing a novel idea for the breeding of highly disease-resistant edible mushrooms and plants.

PagMYB180 regulates adventitious rooting via a ROS/PCD-dependent pathway in poplar

The formation of adventitious roots (AR) is an essential step in the vegetative propagation of economically woody species. Reactive oxygen species (ROS) function as signaling molecules in regulating root growth and development. Here, we identified an R2R3-MYB transcription factor PagMYB180 as a regulator of AR formation in hybrid poplar (Populus alba × Populus glandulosa). PagMYB180 was specifically expressed in the vascular tissues of poplar roots, stems and leaves, and its protein was localized in the nucleus and acted as a transcriptional repressor. Both dominant repression and overexpression of PagMYB180 resulted in a significant reduction of AR quantity, a substantial increase of AR length, and an elevation of both the quantity and length of lateral roots (LR) compared to the wild type (WT) plants. Furthermore, PagMYB180 regulates programmed cell death (PCD) in root cortex cells, which is associated with elevated levels of ROS. Transcriptome and reverse transcription-quantitative PCR (RT-qPCR) analyses revealed that a series of differentially expressed genes are related to ROS, PCD and ethylene synthesis. Taken together, these results suggest that PagMYB180 may regulate AR development via a ROS/PCD-dependent pathway in poplar.

Comparisons of two receptor-MAPK pathways in a single cell-type reveal mechanisms of signalling specificity

Cells harbour numerous receptor pathways to respond to diverse stimuli, yet often share common downstream signalling components. Mitogen-activated protein kinase (MPK) cascades are an example of such common hubs in eukaryotes. How such common hubs faithfully transduce distinct signals within the same cell-type is insufficiently understood, yet of fundamental importance for signal integration and processing in plants. We engineered a unique genetic background allowing direct comparisons of a developmental and an immunity pathway in one cell-type, the Arabidopsis root endodermis. We demonstrate that the two pathways maintain distinct functional and transcriptional outputs despite common MPK activity patterns. Nevertheless, activation of different MPK kinases and MPK classes led to distinct functional readouts, matching observed pathway-specific readouts. On the basis of our comprehensive analysis of core MPK signalling elements, we propose that combinatorial activation within the MPK cascade determines the differential regulation of an endodermal master transcription factor, MYB36, that drives pathway-specific gene activation.

In-depth analysis of isochorismate synthase-derived metabolism in plant immunity: Identification of meta-substituted benzoates and salicyloyl-malate

Isochorismate-derived metabolism enables biosynthesis of the plant defense hormone salicylic acid (SA) and its derivatives. In Arabidopsis thaliana, the stress-induced accumulation of SA depends on ISOCHORISMATE SYNTHASE1 (ICS1) and also requires the presumed isochorismate transporter ENHANCED DISEASE SUSCEPTIBILITY5 (EDS5) and the GH3 enzyme avrPphB SUSCEPTIBLE3 (PBS3). By comparative metabolite and structural analyses, we identified several hitherto unreported ICS1- and EDS5-dependent, biotic stress-inducible Arabidopsis metabolites. These involve meta-substituted SA derivatives (5-formyl-SA, 5-carboxy-SA, 5-carboxymethyl-SA), their benzoic acid (BA) analogs (3-formyl-BA, 3-carboxy-BA, 3-carboxymethyl-BA), and besides the previously detected salicyloyl-aspartate (SA-Asp), the ester conjugate salicyloyl-malate (SA-Mal). SA functions as a biosynthetic precursor for SA-Mal and SA-Asp, but not for the meta-substituted SA- and BA-derivatives, which accumulate to moderate levels at later stages of bacterial infection. Interestingly, Arabidopsis leaves possess oxidizing activity to effectively convert meta-formyl- into meta-carboxy-SA/BAs. In contrast to SA, exogenously applied meta-substituted SA/BA-derivatives and SA-Mal exert a moderate impact on plant immunity and defence-related gene expression. While the isochorismate-derived metabolites are negatively regulated by the SA receptor NON-EXPRESSOR OF PR GENES1, SA conjugates (SA-Mal, SA-Asp, SA-glucose conjugates) and meta-substituted SA/BA-derivatives are oppositely affected by PBS3. Notably, our data indicate a PBS3-independent path to isochorismate-derived SA at later stages of bacterial infection, which does not considerably impact immune-related characteristics. Moreover, our results argue against a previously proposed role of EDS5 in the biosynthesis of the immune signal N-hydroxypipecolic acid and associated transport processes. We propose a significantly extended biochemical scheme of plant isochorismate metabolism that involves an alternative generation mode for benzoate- and salicylate-derivatives.

The RALF2-FERONIA-MYB63 module orchestrates growth and defense in tomato roots

Plant secreted peptides RAPID ALKALINISATION FACTORs (RALFs), which act through the receptor FERONIA (FER), play important roles in plant growth. However, it remains unclear whether and how RALF-FER contributes to the trade-off of plant growth-defense. Here, we used a variety of techniques such as CRISPR/Cas9, protein-protein interaction and transcriptional regulation methods to investigate the role of RALF2 and its receptor FER in regulating lignin deposition, root growth, and defense against Fusarium oxysporum f. sp. lycopersici (Fol) in tomato (Solanum lycopersicum). The ralf2 and fer mutants show reduced primary root length, elevated lignin accumulation, and enhanced resistance against Fol than the wild-type. FER interacts with and phosphorylates MYB63 to promote its degradation. MYB63 serves as an activator of lignin deposition by regulating the transcription of dirigent protein gene DIR19. Mutation of DIR19 suppresses lignin accumulation, and reverses the short root phenotype and Fol resistance in ralf2 or fer mutant. Collectively, our results demonstrate that the RALF2-FER-MYB63 module fine-tunes root growth and resistance against Fol through regulating the deposition of lignin in tomato roots. The study sheds new light on how plants maintain the growth-defense balance via RALF-FER.

Bacillus B2 promotes root growth and enhances phosphorus absorption in apple rootstocks by affecting MhMYB15

Due to the chelation of phosphorus in the soil, it becomes unavailable for plant growth and development. The mechanisms by which phosphorus-solubilizing bacteria activate immobilized phosphorus to promote the growth and development of woody plants, as well as the intrinsic molecular mechanisms, are not clear. Through the analysis of microbial communities in the rhizosphere 16S V3-V4 and a homologous gene encoding microbial alkaline phosphomonoesterase (phoD) in phosphate-efficient (PE) and phosphate-inefficient apple rootstocks, it was found that PE significantly enriched beneficial rhizobacteria. The best phosphorus-solubilizing bacteria, Bacillus sp. strain 7DB1 (B2), was isolated, purified, and identified from the rhizosphere soil of PE rootstocks. Incubating with Bacillus B2 into the rhizosphere of apple rootstocks significantly increased the soluble phosphorus and flavonoid content in the rhizosphere soil. Simultaneously, this process stimulates the root development of the rootstocks and enhances plant phosphorus uptake. After root transcriptome sequencing, candidate transcription factor MhMYB15, responsive to Bacillus B2, was identified through heatmap and co-expression network analysis. Yeast one-hybrid, electrophoretic mobility shift assay, and LUC assay confirmed that MhMYB15 can directly bind to the promoter regions of downstream functional genes, including chalcone synthase MhCHS2 and phosphate transporter MhPHT1;15. Transgenic experiments with MhMYB15 revealed that RNAi-MhMYB15 silenced lines failed to induce an increase in flavonoid content and phosphorus levels in the roots under the treatment of Bacillus B2, and plant growth was slower than the control. In conclusion, MhMYB15 actively responds to Bacillus B2, regulating the accumulation of flavonoids and the uptake of phosphorus, thereby influencing plant growth and development.

Serine hydroxymethyltransferase6 is involved in growth and resistance against pathogens via ethylene and lignin production in Arabidopsis

Photorespiratory serine hydroxymethyltransferases (SHMTs) are important enzymes of cellular one-carbon metabolism. In this study, we investigated the potential role of SHMT6 in Arabidopsis thaliana. We found that SHMT6 is localized in the nucleus and expressed in different tissues during development. Interestingly SHMT6 is inducible in response to avirulent, virulent Pseudomonas syringae and to Fusarium oxysporum infection. Overexpression of SHMT6 leads to larger flowers, siliques, seeds, roots, and consequently an enhanced overall biomass. This enhanced growth was accompanied by increased stomatal conductance and photosynthetic capacity as well as ATP, protein, and chlorophyll levels. By contrast, a shmt6 knockout mutant displayed reduced growth. When challenged with Pseudomonas syringae pv tomato (Pst) DC3000 expressing AvrRpm1, SHMT6 overexpression lines displayed a clear hypersensitive response which was characterized by enhanced electrolyte leakage and reduced bacterial growth. In response to virulent Pst DC3000, the shmt6 mutant developed severe disease symptoms and becomes very susceptible, whereas SHMT6 overexpression lines showed enhanced resistance with increased expression of defense pathway associated genes. In response to Fusarium oxysporum, overexpression lines showed a reduction in symptoms. Moreover, SHMT6 overexpression lead to enhanced production of ethylene and lignin, which are important components of the defense response. Collectively, our data revealed that SHMT6 plays an important role in development and defense against pathogens.

Combined metabolome and transcriptome reveal HmF6'H1 regulating simple coumarin accumulation against powdery mildew infection in Heracleum moellendorffii Hance

BACKGROUND

Powdery mildew, caused by Eeysiphe heraclei, seriously threatens Heracleum moellendorffii Hance. Plant secondary metabolites are essential to many activities and are necessary for defense against biotic stress. In order to clarify the functions of these metabolites in response to the pathogen, our work concentrated on the variations in the accumulation of secondary metabolites in H. moellendorffii during E. heraclei infection.

RESULTS

Following E. heraclei infection, a significant upregulation of coumarin metabolites-particularly simple coumarins and associated genes was detected by RNA-seq and UPLC-MS/MS association analysis. Identifying HmF6'H1, a Feruloyl CoA 6'-hydroxylase pivotal in the biosynthesis of the coumarin basic skeleton through ortho-hydroxylation, was a significant outcome. The cytoplasmic HmF6'H1 protein was shown to be able to catalyze the ortho-hydroxylation of p-coumaroyl-CoA and caffeoyl-CoA, resulting in the formation of umbelliferone and esculetin, respectively. Over-expression of the HmF6'H1 gene resulted in increased levels of simple coumarins, inhibiting the biosynthesis of furanocoumarins and pyranocoumarins by suppressing PT gene expression, enhancing H. moellendorffii resistance to powdery mildew.

CONCLUSIONS

These results established HmF6'H1 as a resistance gene aiding H. moellendorffii in combatting E. heraclei infection, offering additional evidence of feruloyl-CoA 6'-hydroxylase role in catalyzing various types of simple coumarins. Therefore, this work contributes to our understanding of the function of simple coumarins in plants' defense against powdery mildew infection.

Transcriptome responses of Arabidopsis to necrotrophic fungus Alternaria brassicae reveal pathways and candidate genes associated with resistance

Alternaria leaf blight (ALB), caused by a necrotrophic fungus Alternaria brassicae is a serious disease of oleiferous Brassicas resulting in significant yield losses worldwide. No robust resistance against A. brassicae has been identified in the Brassicas. Natural accessions of Arabidopsis show a spectrum of responses to A. brassicae ranging from high susceptibility to complete resistance. To understand the molecular mechanisms of resistance/ susceptibility, we analysed the comparative changes in the transcriptome profile of Arabidopsis accessions with contrasting responses- at different time points post-infection. Differential gene expression, GO enrichment, pathway enrichment, and weighted gene co-expression network analysis (WGCNA) revealed reprogramming of phenylpropanoid biosynthetic pathway involving lignin, hydroxycinnamic acids, scopoletin, anthocyanin genes to be highly associated with resistance against A. brassicae. T-DNA insertion mutants deficient in the biosynthesis of coumarin scopoletin exhibited enhanced susceptibility to A. brassicae. The supplementation of scopoletin to medium or exogenous application resulted in a significant reduction in the A. brassicae growth. Our study provides new insights into the transcriptome dynamics in A. brassicae-challenged Arabidopsis and demonstrates the involvement of coumarins in plant immunity against the Brassica pathogen A. brassicae.

Employing Genomic Tools to Explore the Molecular Mechanisms behind the Enhancement of Plant Growth and Stress Resilience Facilitated by a Burkholderia Rhizobacterial Strain

The rhizobacterial strain BJ3 showed 16S rDNA sequence similarity to species within the Burkholderia genus. Its complete genome sequence revealed a 97% match with Burkholderia contaminans and uncovered gene clusters essential for plant-growth-promoting traits (PGPTs). These clusters include genes responsible for producing indole acetic acid (IAA), osmolytes, non-ribosomal peptides (NRPS), volatile organic compounds (VOCs), siderophores, lipopolysaccharides, hydrolytic enzymes, and spermidine. Additionally, the genome contains genes for nitrogen fixation and phosphate solubilization, as well as a gene encoding 1-aminocyclopropane-1-carboxylate (ACC) deaminase. The treatment with BJ3 enhanced root architecture, boosted vegetative growth, and accelerated early flowering in Arabidopsis. Treated seedlings also showed increased lignin production and antioxidant capabilities, as well as notably increased tolerance to water deficit and high salinity. An RNA-seq transcriptome analysis indicated that BJ3 treatment significantly activated genes related to immunity induction, hormone signaling, and vegetative growth. It specifically activated genes involved in the production of auxin, ethylene, and salicylic acid (SA), as well as genes involved in the synthesis of defense compounds like glucosinolates, camalexin, and terpenoids. The expression of AP2/ERF transcription factors was markedly increased. These findings highlight BJ3's potential to produce various bioactive metabolites and its ability to activate auxin, ethylene, and SA signaling in Arabidopsis, positioning it as a new Burkholderia strain that could significantly improve plant growth, stress resilience, and immune function.

SA and NHP glucosyltransferase UGT76B1 affects plant defense in both SID2- and NPR1-dependent and independent manner

KEY MESSAGE

The small-molecule glucosyltransferase loss-of-function mutant ugt76b1 exhibits both SID2- or NPR1-dependent and independent facets of enhanced plant immunity, whereupon FMO1 is required for the SID2 and NPR1 independence. The small-molecule glucosyltransferase UGT76B1 inactivates salicylic acid (SA), isoleucic acid (ILA), and N-hydroxypipecolic acid (NHP). ugt76b1 loss-of-function plants manifest an enhanced defense status. Thus, we were interested how UGT76B1 genetically integrates in defense pathways and whether all impacts depend on SA and NHP. We study the integration of UGT76B1 by transcriptome analyses of ugt76b1. The comparison of transcripts altered by the loss of UGT76B1 with public transcriptome data reveals both SA-responsive, ISOCHORISMATE SYNTHASE 1/SALICYLIC ACID INDUCTION DEFICIENT 2 (ICS1/SID2)- and NON EXPRESSOR OF PR GENES 1 (NPR1)-dependent, consistent with the role of UGT76B1 in glucosylating SA, and SA-non-responsive, SID2/NPR1-independent genes. We also discovered that UGT76B1 impacts on a group of genes showing non-SA-responsiveness and regulation by infections independent from SID2/NPR1. Enhanced resistance of ugt76b1 against Pseudomonas syringae is partially independent from SID2 and NPR1. In contrast, the ugt76b1-activated resistance is completely dependent on FMO1 encoding the NHP-synthesizing FLAVIN-DEPENDENT MONOOXYGENASE 1). Moreover, FMO1 ranks top among the ugt76b1-induced SID2- and NPR1-independent pathogen responsive genes, suggesting that FMO1 determines the SID2- and NPR1-independent effect of ugt76b1. Furthermore, the genetic study revealed that FMO1, ENHANCED DISEASE SUSCEPTIBILITY 1 (EDS1), SID2, and NPR1 are required for the SA-JA crosstalk and senescence development of ugt76b1, indicating that EDS1 and FMO1 have a similar effect like stress-induced SA biosynthesis (SID2) or the key SA signaling regulator NPR1. Thus, UGT76B1 influences both SID2/NPR1-dependent and independent plant immunity, and the SID2/NPR1 independence is relying on FMO1 and its product NHP, another substrate of UGT76B1.

Genomic and transcriptomic studies on flavonoid biosynthesis in Lagerstroemia indica

BACKGROUND

Lagerstroemia indica is a widely cultivated ornamental woody shrub/tree of the family Lythraceae that is used as a traditional medicinal plant in East Asia and Egypt. However, unlike other ornamental woody plants, its genome is not well-investigated, which hindered the discovery of the key genes that regulate important traits and the synthesis of bioactive compounds.

RESULTS

In this study, the genomic sequences of L. indica were determined using several next-generation sequencing technologies. Altogether, 324.01 Mb sequences were assembled and 98.21% (318.21 Mb) of them were placed in 24 pseudo-chromosomes. The heterozygosity, repeated sequences, and GC residues occupied 1.65%, 29.17%, and 38.64% of the genome, respectively. In addition, 28,811 protein-coding gene models, 327 miRNAs, 552 tRNAs, 214 rRNAs, and 607 snRNAs were identified. The intra- and interspecies synteny and Ks analysis revealed that L. indica exhibits a hexaploidy. The co-expression profiles of the genes involved in the phenylpropanoid (PA) and flavonoid/anthocyanin (ABGs) pathways with the R2R3 MYB genes (137 members) showed that ten R2R3 MYB genes positively regulate flavonoid/anthocyanin biosynthesis. The colors of flowers with white, purple (PB), and deep purplish pink (DPB) petals were found to be determined by the levels of delphinidin-based (Dp) derivatives. However, the substrate specificities of LiDFR and LiOMT probably resulted in the different compositions of flavonoid/anthocyanin. In L. indica, two LiTTG1s (LiTTG1-1 and LiTTG1-2) were found to be the homologs of AtTTG1 (WD40). LiTTG1-1 was found to repress anthocyanin biosynthesis using the tobacco transient transfection assay.

CONCLUSIONS

This study showed that the ancestor L. indica experienced genome triplication approximately 38.5 million years ago and that LiTTG1-1 represses anthocyanin biosynthesis. Furthermore, several genes such as LiDFR, LiOMTs, and R2R3 LiMYBs are related to anthocyanin biosynthesis. Further studies are required to clarify the mechanisms and alleles responsible for flower color development.

Natural variation in the pattern-triggered immunity response in plants: Investigations, implications and applications

The pattern-triggered immunity (PTI) response is triggered at the plant cell surface by the recognition of microbe-derived molecules known as microbe- or pathogen-associated molecular patterns or molecules derived from compromised host cells called damage-associated molecular patterns. Membrane-localized receptor proteins, known as pattern recognition receptors, are responsible for this recognition. Although much of the machinery of PTI is conserved, natural variation for the PTI response exists within and across species with respect to the components responsible for pattern recognition, activation of the response, and the strength of the response induced. This review describes what is known about this variation. We discuss how variation in the PTI response can be measured and how this knowledge might be utilized in the control of plant disease and in developing plant varieties with enhanced disease resistance.

Lignin Biosynthesis and Its Diversified Roles in Disease Resistance

Lignin is complex, three-dimensional biopolymer existing in plant cell wall. Lignin biosynthesis is increasingly highlighted because it is closely related to the wide applications in agriculture and industry productions, including in pulping process, forage digestibility, bio-fuel, and carbon sequestration. The functions of lignin in planta have also attracted more attentions recently, particularly in plant defense response against different pathogens. In this brief review, the progress in lignin biosynthesis is discussed, and the lignin's roles in disease resistance are thoroughly elucidated. This issue will help in developing broad-spectrum resistant crops in agriculture.

A combination of conserved and diverged responses underlies Theobroma cacao's defense response to Phytophthora palmivora

BACKGROUND

Plants have complex and dynamic immune systems that have evolved to resist pathogens. Humans have worked to enhance these defenses in crops through breeding. However, many crops harbor only a fraction of the genetic diversity present in wild relatives. Increased utilization of diverse germplasm to search for desirable traits, such as disease resistance, is therefore a valuable step towards breeding crops that are adapted to both current and emerging threats. Here, we examine diversity of defense responses across four populations of the long-generation tree crop Theobroma cacao L., as well as four non-cacao Theobroma species, with the goal of identifying genetic elements essential for protection against the oomycete pathogen Phytophthora palmivora.

RESULTS

We began by creating a new, highly contiguous genome assembly for the P. palmivora-resistant genotype SCA 6 (Additional file 1: Tables S1-S5), deposited in GenBank under accessions CP139290-CP139299. We then used this high-quality assembly to combine RNA and whole-genome sequencing data to discover several genes and pathways associated with resistance. Many of these are unique, i.e., differentially regulated in only one of the four populations (diverged 40 k-900 k generations). Among the pathways shared across all populations is phenylpropanoid biosynthesis, a metabolic pathway with well-documented roles in plant defense. One gene in this pathway, caffeoyl shikimate esterase (CSE), was upregulated across all four populations following pathogen treatment, indicating its broad importance for cacao's defense response. Further experimental evidence suggests this gene hydrolyzes caffeoyl shikimate to create caffeic acid, an antimicrobial compound and known inhibitor of Phytophthora spp.

CONCLUSIONS

Our results indicate most expression variation associated with resistance is unique to populations. Moreover, our findings demonstrate the value of using a broad sample of evolutionarily diverged populations for revealing the genetic bases of cacao resistance to P. palmivora. This approach has promise for further revealing and harnessing valuable genetic resources in this and other long-generation plants.

Integrated physiological, metabolomic, and transcriptomic analyses elucidate the regulation mechanisms of lignin synthesis under osmotic stress in alfalfa leaf (Medicago sativa L.)

Alfalfa, an essential forage crop known for its high yield, nutritional value, and strong adaptability, has been widely cultivated worldwide. The yield and quality of alfalfa are frequently jeopardized due to environmental degradation. Lignin, a constituent of the cell wall, enhances plant resistance to abiotic stress, which often causes osmotic stress in plant cells. However, how lignin responds to osmotic stress in leaves remains unclear. This study explored the effects of osmotic stress on lignin accumulation and the contents of intermediate metabolites involved in lignin synthesis in alfalfa leaves. Osmotic stress caused an increase in lignin accumulation and the alteration of core enzyme activities and gene expression in the phenylpropanoid pathway. We identified five hub genes (CSE, CCR, CADa, CADb, and POD) and thirty edge genes (including WRKYs, MYBs, and UBPs) by integrating transcriptome and metabolome analyses. In addition, ABA and ethylene signaling induced by osmotic stress regulated lignin biosynthesis in a contradictory way. These findings contribute to a new theoretical foundation for the breeding of high-quality and resistant alfalfa varieties.

Insights into the early transcriptomic response against watermelon mosaic virus in melon

BACKGROUND

Watermelon mosaic virus (WMV) is one of the most prevalent viruses affecting melon worldwide. Recessive resistance to WMV in melon has previously been reported in the African accession TGR-1551. Moreover, the genomic regions associated to the resistance have also been described. Nevertheless, the transcriptomic response that might infer the resistance to this potyvirus has not been explored.

RESULTS

We have performed a comparative transcriptomic analysis using mock and WMV-inoculated plants of the susceptible cultivar "Bola de oro" (BO) and a resistant RIL (Recombinant inbred line) derived from the initial cross between "TGR-1551" and BO. In total, 616 genes were identified as differentially expressed and the weighted gene co-expression network analysis (WGCNA) detected 19 gene clusters (GCs), of which 7 were differentially expressed for the genotype x treatment interaction term. SNPs with a predicted high impact on the protein function were detected within the coding regions of most of the detected DEGs. Moreover, 3 and 16 DEGs were detected within the QTL regions previously described in chromosomes 11 and 5, respectively. In addition to these two specific genomic regions, we also observde large transcriptomic changes from genes spread across the genome in the resistant plants in response to the virus infection. This early response against WMV implied genes involved in plant-pathogen interaction, plant hormone signal transduction, the MAPK signaling pathway or ubiquitin mediated proteolysis, in detriment to the photosynthetic and basal metabolites pathways. Moreover, the gene MELO3C021395, which coded a mediator of RNA polymerase II transcription subunit 33A (MED33A), has been proposed as the candidate gene located on chromosome 11 conferring resistance to WMV.

CONCLUSIONS

The comparative transcriptomic analysis presented here showed that, even though the resistance to WMV in TGR-1551 has a recessive nature, it triggers an active defense response at a transcriptomic level, which involves broad-spectrum resistance mechanisms. Thus, this study represents a step forward on our understanding of the mechanisms underlaying WMV resistance in melon. In addition, it sheds light into a broader topic on the mechanisms of recessive resistances.

A chromosome-scale genome of Peucedanum praeruptorum provide insights into Apioideae evolution and medicinal ingredient biosynthesis

Peucedanum praeruptorum Dunn, a traditional Chinese medicine rich in coumarin, belongs to the Apiaceae family. A high-quality assembled genome of P. praeruptorum is lacking, which has posed obstacles to functional identification and molecular evolution studies of genes associated with coumarin production. Here, a chromosome-scale reference genome of P. praeruptorum, an important medicinal and aromatic plant, was first sequenced and assembled using Oxford Nanopore Technologies and Hi-C sequencing. The final assembled genome size was 1.83 Gb, with a contig N50 of 11.12 Mb. The entire BUSCO evaluation and second-generation read comparability rates were 96.0 % and 99.31 %, respectively. Furthermore, 99.91 % of the genome was anchored to 11 pseudochromosomes. The comparative genomic study revealed the presence of 18,593 orthogroups, which included 476 species-specific orthogroups and 1211 expanded gene families. Two whole-genome duplication (WGD) events and one whole-genome triplication (WGT) event occurred in P. praeruptorum. In addition to the γ-WGT shared by core eudicots or most eudicots, the first WGD was shared by Apiales, while the most recent WGD was unique to Apiaceae. Our study demonstrated that WGD events that occurred in Apioideae highlighted the important role of tandem duplication in the biosynthesis of coumarins and terpenes in P. praeruptorum. Additionally, the expansion of the cytochrome P450 monooxygenase, O-methyltransferase, ATP-binding cassette (ABC) transporter, and terpene synthase families may be associated with the abundance of coumarins and terpenoids. Moreover, we identified >170 UDP-glucosyltransferase members that may be involved in the glycosylation post-modification of coumarins. Significant gene expansion was observed in the ABCG, ABCB, and ABCC subgroups of the ABC transporter family, potentially facilitating the transmembrane transport of coumarins after bolting. The P. praeruptorum genome provides valuable insights into the machinery of coumarin biosynthesis and enhances our understanding of Apiaceae evolution.

The Characterization of R2R3-MYB Genes in Ammopiptanthus nanus Uncovers That the miR858-AnaMYB87 Module Mediates the Accumulation of Anthocyanin under Osmotic Stress

R2R3-MYB transcription factors (TFs) participate in the modulation of plant development, secondary metabolism, and responses to environmental stresses. Ammopiptanthus nanus, a leguminous dryland shrub, tolerates a high degree of environmental stress, including drought and low-temperature stress. The systematic identification, structural analysis, evolutionary analysis, and gene profiling of R2R3-MYB TFs under cold and osmotic stress in A. nanus were performed. Up to 137 R2R3-MYB TFs were identified and clustered into nine clades, with most A. nanus R2R3-MYB members belonging to clade VIII. Tandem and segmental duplication events drove the expansion of the A. nanus R2R3-MYB family. Expression profiling revealed that multiple R2R3-MYB genes significantly changed under osmotic and cold stress conditions. MiR858 and miR159 targeted 88 R2R3-MYB genes. AnaMYB87, an miR858-targeted clade VIII R2R3-MYB TF, was up-regulated under both osmotic and cold stress. A transient expression assay in apples showed that the overexpression of AnaMYB87 promoted anthocyanin accumulation. A luciferase reporter assay in tobacco demonstrated that AnaMYB87 positively affected the transactivation of the dihydroflavonol reductase gene, indicating that the miR858-MYB87 module mediates anthocyanin accumulation under osmotic stress by regulating the dihydroflavonol reductase gene in A. nanus. This study provides new data to understand the roles of R2R3-MYB in plant stress responses.

Restraining Quiescence Release-Related Ageing in Plant Cells: A Case Study in Carrot

The blackening of cut carrots causes substantial economic losses to the food industry. Blackening was not observed in carrots that had been stored underground for less than a year, but the susceptibility to blackening increased with the age of the carrots that were stored underground for longer periods. Samples of black, border, and orange tissues from processed carrot batons and slices, prepared under industry standard conditions, were analyzed to identify the molecular and metabolic mechanisms underpinning processing-induced blackening. The black tissues showed substantial molecular and metabolic rewiring and large changes in the cell wall structure, with a decreased abundance of xyloglucan, pectins (homogalacturonan, rhamnogalacturonan-I, galactan and arabinan), and higher levels of lignin and other phenolic compounds when compared to orange tissues. Metabolite profiling analysis showed that there was a major shift from primary to secondary metabolism in the black tissues, which were depleted in sugars, amino acids, and tricarboxylic acid (TCA) cycle intermediates but were rich in phenolic compounds. These findings suggest that processing triggers a release from quiescence. Transcripts encoding proteins associated with secondary metabolism were less abundant in the black tissues, but there were no increases in transcripts associated with oxidative stress responses, programmed cell death, or senescence. We conclude that restraining quiescence release alters cell wall metabolism and composition, particularly regarding pectin composition, in a manner that increases susceptibility to blackening upon processing.

The PcMYB44-mediated miR397-PcLACs module regulates defence-induced lignification in pear resistance to fungal disease

Diseases caused by Alternaria alternata and Botryosphaeria dothidea diminish pear yield and quality, and restrict the pear agricultural industry. Lignification is a conserved mechanism for plant resistance against pathogen invasion. The regulatory mechanisms underlying defence-induced lignification in pear in response to fungal pathogen infection remain unknown. In this study, analysis of lignification level and lignin content in pear revealed that A. alternata and B. dothidea induced lignification, and transcriptomics showed that lignin biosynthesis was affected. To explore whether laccases (LACs) mediated by miR397 regulate lignification in pear, we investigated the role of PcmiR397 in repressing the expression of PcLACs using 5'-RNA ligase-mediated-RACE and co-transformation in tobacco. Opposite expression patterns for PcmiR397 and PcLAC target genes were observed in pear in response to pathogens. Transient transformation in pear demonstrated that silencing PcmiR397 and overexpressing a single PcLAC enhanced resistance to pathogens via lignin synthesis. To further reveal the mechanism underpinning the PcMIR397 response of pear to pathogens, the PcMIR397 promoter was analysed, and pMIR397-1039 was found to be inhibited by pathogen infection. The transcription factor PcMYB44 was up-regulated, and it bound to the PcMIR397 promoter and inhibited transcription following pathogen infection. The results demonstrate the role of PcmiR397-PcLACs in broad-spectrum resistance to fungal disease, and the potential role of PcMYB44 involved in the miR397-PcLAC module in regulating defence-induced lignification. The findings provide valuable candidate gene resources and guidance for molecular breeding to improve resistance to fungal disease in pear.

A bacterial type III effector targets plant vesicle-associated membrane proteins

The soilborne bacterial pathogen Ralstonia solanacearum is one of the most destructive plant pathogens worldwide, and its infection process involves the manipulation of numerous plant cellular functions. In this work, we found that the R. solanacearum effector protein RipD partially suppressed different levels of plant immunity triggered by R. solanacearum elicitors, including specific responses triggered by pathogen-associated molecular patterns and secreted effectors. RipD localized in different subcellular compartments in plant cells, including vesicles, and its vesicular localization was enriched in cells undergoing R. solanacearum infection, suggesting that this specific localization may be particularly relevant during infection. Among RipD-interacting proteins, we identified plant vesicle-associated membrane proteins (VAMPs). We also found that overexpression of Arabidopsis thaliana VAMP721 and VAMP722 in Nicotiana benthamiana leaves promoted resistance to R. solanacearum, and this was abolished by the simultaneous expression of RipD, suggesting that RipD targets VAMPs to contribute to R. solanacearum virulence. Among proteins secreted in VAMP721/722-containing vesicles, CCOAOMT1 is an enzyme required for lignin biosynthesis, and mutation of CCOAOMT1 enhanced plant susceptibility to R. solanacearum. Altogether our results reveal the contribution of VAMPs to plant resistance against R. solanacearum and their targeting by a bacterial effector as a pathogen virulence strategy.

Temporal transcriptomic profiling elucidates sorghum defense mechanisms against sugarcane aphids

BACKGROUND

The sugarcane aphid (SCA; Melanaphis sacchari) has emerged as a key pest on sorghum in the United States that feeds from the phloem tissue, drains nutrients, and inflicts physical damage to plants. Previously, it has been shown that SCA reproduction was low and high on sorghum SC265 and SC1345 plants, respectively, compared to RTx430, an elite sorghum male parental line (reference line). In this study, we focused on identifying the defense-related genes that confer resistance to SCA at early and late time points in sorghum plants with varied levels of SCA resistance.

RESULTS

We used RNA-sequencing approach to identify the global transcriptomic responses to aphid infestation on RTx430, SC265, and SC1345 plants at early time points 6, 24, and 48 h post infestation (hpi) and after extended period of SCA feeding for 7 days. Aphid feeding on the SCA-resistant line upregulated the expression of 3827 and 2076 genes at early and late time points, respectively, which was relatively higher compared to RTx430 and SC1345 plants. Co-expression network analysis revealed that aphid infestation modulates sorghum defenses by regulating genes corresponding to phenylpropanoid metabolic pathways, secondary metabolic process, oxidoreductase activity, phytohormones, sugar metabolism and cell wall-related genes. There were 187 genes that were highly expressed during the early time of aphid infestation in the SCA-resistant line, including genes encoding leucine-rich repeat (LRR) proteins, ethylene response factors, cell wall-related, pathogenesis-related proteins, and disease resistance-responsive dirigent-like proteins. At 7 days post infestation (dpi), 173 genes had elevated expression levels in the SCA-resistant line and were involved in sucrose metabolism, callose formation, phospholipid metabolism, and proteinase inhibitors.

CONCLUSIONS

In summary, our results indicate that the SCA-resistant line is better adapted to activate early defense signaling mechanisms in response to SCA infestation because of the rapid activation of the defense mechanisms by regulating genes involved in monolignol biosynthesis pathway, oxidoreductase activity, biosynthesis of phytohormones, and cell wall composition. This study offers further insights to better understand sorghum defenses against aphid herbivory.

Two R2R3-MYB transcription factors from Chinese cedar (Cryptomeria fortunei Hooibrenk) are involved in the regulation of secondary cell wall formation

As the most abundant renewable energy source, wood comprises the secondary cell wall (SCW). SCW biosynthesis involves lignin and cellulose deposition. Increasing studies have illustrated that R2R3-MYB transcription factors (TFs) play pivotal roles in affecting lignin accumulation and SCW formation. Nevertheless, the regulatory roles of R2R3-MYBs are still unresolved in Cryptomeria fortunei Hooibrenk cambium and wood formation. To dissect the potentials of CfMYBs, we successfully cloned and intensively studied the functions of CfMYB4 and CfMYB5 in SCW formation and abiotic stress response. They both contained the conserved MYB domain capable of forming a special structure that could bind to the core motifs of downstream genes. The phylogenetic tree implied that two CfMYBs clustered into different evolutionary branches. They were predominantly expressed in the stem and were localized to the nucleus. Furthermore, CfMYB4 functioned as an activator to enhance lignin and cellulose accumulation, and increase the SCW thickness by elevating the expression levels of SCW-related genes. By contrast, CfMYB5 negatively regulated lignin and cellulose biosynthesis, and decreased SCW formation by reducing the expression of SCW biosynthetic genes. Our data not only highlight the regulatory functions of CfMYBs in lignin deposition but also provide critical insights into the development of strategies for the genetic improvement of Cryptomeria fortunei wood biomass.

CsMYB15 positively regulates Cs4CL2-mediated lignin biosynthesis during juice sac granulation in navel orange

'Lane Late', a late-maturing navel orange cultivar, is mainly distributed in the Three Gorges Reservoir area, which matures in the late March of the next year and needs overwintering cultivation. Citrus fruit granulation is a physiological disorder, which is characterized by lignification and dehydration of juice sac cells, seriously affecting the commercial value of citrus fruits. The pre-harvest granulation of late-maturing navel orange is main caused by low temperature in the winter, but its mechanism and regulation pattern remain unclear. In this study, a SG2-type R2R3-MYB transcription factor, CsMYB15, was identified from Citrus sinensis, which was significantly induced by both juice sac granulation and low temperature treatment. Subcellular localization analysis and transcriptional activation assay revealed that CsMYB15 protein was localized to the nucleus, and it exhibited transcriptional activation activity in yeast. Over-expression of CsMYB15 by stable transformation in navel orange calli and transient transformation in kumquat fruits and navel orange juice sacs significantly increased lignin content in the transgenic lines. Further, Yeast one hybrid, EMSA, and LUC assays demonstrated that CsMYB15 directly bound to the Cs4CL2 promoter and activated its expression, thereby causing a high accumulation of lignin in citrus. Taken together, these results elucidated the biological function of CsMYB15 in regulating Cs4CL2-mediated lignin biosynthesis, and provided novel insight into the transcriptional regulation mechanism underlying the juice sac granulation of late-maturing navel orange.

The pivotal role of MYB transcription factors in plant disease resistance

MAIN CONCLUSION

MYB transcription factors are essential for diverse biology processes in plants. This review has focused on the potential molecular actions of MYB transcription factors in plant immunity. Plants possess a variety of molecules to defend against disease. Transcription factors (TFs) serve as gene connections in the regulatory networks controlling plant growth and defense against various stressors. As one of the largest TF families in plants, MYB TFs coordinate molecular players that modulate plant defense resistance. However, the molecular action of MYB TFs in plant disease resistance lacks a systematic analysis and summary. Here, we describe the structure and function of the MYB family in the plant immune response. Functional characterization revealed that MYB TFs often function either as positive or negative modulators towards different biotic stressors. Moreover, the MYB TF resistance mechanisms are diverse. The potential molecular actions of MYB TFs are being analyzed to uncover functions by controlling the expression of resistance genes, lignin/flavonoids/cuticular wax biosynthesis, polysaccharide signaling, hormone defense signaling, and the hypersensitivity response. MYB TFs have a variety of regulatory modes that fulfill pivotal roles in plant immunity. MYB TFs regulate the expression of multiple defense genes and are, therefore, important for increasing plant disease resistance and promoting agricultural production.

Genome-wide identification and expression analyses of phenylalanine ammonia-lyase gene family members from tomato (Solanum lycopersicum) reveal their role in root-knot nematode infection

Phenylalanine ammonia-lyase (PAL) is a key enzyme and rate-limiting enzyme of phenylpropanoid metabolism, which is a very important pathway in plants, and the secondary products it produces play an important role in plant growth and development, disease resistance, and stress resistance responses. However, PALs still lack systematic characterization in tomato. Based on a bioinformatics methods, PAL family genes were identified and characterized from tomato. qRT-PCR was used to study the expression of PAL genes in cultivated tomato after root-knot nematode infection. In this study, 14 and 11 PAL genes were identified in cultivated and wild tomatoes, and phylogenetic analysis classified them into three subfamilies, with different subfamilies of PAL proteins evolving in different directions in monocotyledonous and dicotyledonous plants. The extensive presence of stress, growth, hormone, and light response elements in the promoter sequences of SlPAL (Solanum lycopersicum) and SpenPAL (Solanum pennellii) genes suggests that this family has a critical role in abiotic stress. Collinearity indicates that members of the tomato and Arabidopsis PAL genes family are from the same ancestor, and the SlPAL10 gene is directly homologous to monocotyledonous rice and maize, suggesting that the SlPAL10 gene was present before monocotyledonous differentiation. Two co-expressed gene modules containing PAL genes were screened by WGCNA, and the core genes in the network were mined and functionally annotated by calculating the connectivity of genes within the modules. In addition, the expression of some genes changed significantly after root-knot nematode infection, with up-regulation of 4 genes and down-regulation of 3 genes. This result provides a data reference for the study of PAL family gene functions in tomato, and also provides a potential application for the subsequent selection of PAL genes in tomato for root-knot nematode resistance.

Strigolactones positively regulate Verticillium wilt resistance in cotton via crosstalk with other hormones

Verticillium wilt caused by Verticillium dahliae is a serious vascular disease in cotton (Gossypium spp.). V. dahliae induces the expression of the CAROTENOID CLEAVAGE DIOXYGENASE 7 (GauCCD7) gene involved in strigolactone (SL) biosynthesis in Gossypium australe, suggesting a role for SLs in Verticillium wilt resistance. We found that the SL analog rac-GR24 enhanced while the SL biosynthesis inhibitor TIS108 decreased cotton resistance to Verticillium wilt. Knock-down of GbCCD7 and GbCCD8b genes in island cotton (Gossypium barbadense) decreased resistance, whereas overexpression of GbCCD8b in upland cotton (Gossypium hirsutum) increased resistance to Verticillium wilt. Additionally, Arabidopsis (Arabidopsis thaliana) SL mutants defective in CCD7 and CCD8 putative orthologs were susceptible, whereas both Arabidopsis GbCCD7- and GbCCD8b-overexpressing plants were more resistant to Verticillium wilt than wild-type (WT) plants. Transcriptome analyses showed that several genes related to the jasmonic acid (JA)- and abscisic acid (ABA)-signaling pathways, such as MYELOCYTOMATOSIS 2 (GbMYC2) and ABA-INSENSITIVE 5, respectively, were upregulated in the roots of WT cotton plants in responses to rac-GR24 and V. dahliae infection but downregulated in the roots of both GbCCD7- and GbCCD8b-silenced cotton plants. Furthermore, GbMYC2 suppressed the expression of GbCCD7 and GbCCD8b by binding to their promoters, which might regulate the homeostasis of SLs in cotton through a negative feedback loop. We also found that GbCCD7- and GbCCD8b-silenced cotton plants were impaired in V. dahliae-induced reactive oxygen species (ROS) accumulation. Taken together, our results suggest that SLs positively regulate cotton resistance to Verticillium wilt through crosstalk with the JA- and ABA-signaling pathways and by inducing ROS accumulation.

Exploring the Biologically Active Metabolites Produced by Bacillus cereus for Plant Growth Promotion, Heat Stress Tolerance, and Resistance to Bacterial Soft Rot in Arabidopsis

Eight gene clusters responsible for synthesizing bioactive metabolites associated with plant growth promotion were identified in the Bacillus cereus strain D1 (BcD1) genome using the de novo whole-genome assembly method. The two largest gene clusters were responsible for synthesizing volatile organic compounds (VOCs) and encoding extracellular serine proteases. The treatment with BcD1 resulted in an increase in leaf chlorophyll content, plant size, and fresh weight in Arabidopsis seedlings. The BcD1-treated seedlings also accumulated higher levels of lignin and secondary metabolites including glucosinolates, triterpenoids, flavonoids, and phenolic compounds. Antioxidant enzyme activity and DPPH radical scavenging activity were also found to be higher in the treated seedlings as compared with the control. Seedlings pretreated with BcD1 exhibited increased tolerance to heat stress and reduced disease incidence of bacterial soft rot. RNA-seq analysis showed that BcD1 treatment activated Arabidopsis genes for diverse metabolite synthesis, including lignin and glucosinolates, and pathogenesis-related proteins such as serine protease inhibitors and defensin/PDF family proteins. The genes responsible for synthesizing indole acetic acid (IAA), abscisic acid (ABA), and jasmonic acid (JA) were expressed at higher levels, along with WRKY transcription factors involved in stress regulation and MYB54 for secondary cell wall synthesis. This study found that BcD1, a rhizobacterium producing VOCs and serine proteases, is capable of triggering the synthesis of diverse secondary metabolites and antioxidant enzymes in plants as a defense strategy against heat stress and pathogen attack.

Elicitor-induced plant immunity relies on amino acids accumulation to delay the onset of bacterial virulence

Plant immunity relies on the perception of microbe-associated molecular patterns (MAMPs) from invading microbes to induce defense responses that suppress attempted infections. It has been proposed that MAMP-triggered immunity (MTI) suppresses bacterial infections by suppressing the onset of bacterial virulence. However, the mechanisms by which plants exert this action are poorly understood. Here, we showed that MAMP perception in Arabidopsis (Arabidopsis thaliana) induces the accumulation of free amino acids in a salicylic acid (SA)-dependent manner. When co-infiltrated with Glutamine and Serine, two of the MAMP-induced highly accumulating amino acids, Pseudomonas syringae pv. tomato DC3000 expressed low levels of virulence genes and failed to produce robust infections in otherwise susceptible plants. When applied exogenously, Glutamine and Serine directly suppressed bacterial virulence and growth, bypassing MAMP perception and SA signaling. In addition, an increased level of endogenous Glutamine in the leaf apoplast of a gain-of-function mutant of Glutamine Dumper-1 rescued the partially compromised bacterial virulence- and growth-suppressing phenotype of the SA-induced deficient-2 (sid2) mutant. Our data suggest that MTI suppresses bacterial infections by delaying the onset of virulence with an excess of amino acids at the early stages of infection.

Gene enrichment and co-expression analysis shed light on transcriptional responses to Ralstonia solanacearum in tomato

BACKGROUND

Tomato (Solanum lycopersicum) is both an important agricultural product and an excellent model system for studying plant-pathogen interactions. It is susceptible to bacterial wilt caused by Ralstonia solanacearum (Rs), and infection can result in severe yield and quality losses. To investigate which genes are involved in the resistance response to this pathogen, we sequenced the transcriptomes of both resistant and susceptible tomato inbred lines before and after Rs inoculation.

RESULTS

In total, 75.02 Gb of high-quality reads were generated from 12 RNA-seq libraries. A total of 1,312 differentially expressed genes (DEGs) were identified, including 693 up-regulated and 621 down-regulated genes. Additionally, 836 unique DEGs were obtained when comparing two tomato lines, including 27 co-expression hub genes. A total of 1,290 DEGs were functionally annotated using eight databases, most of which were found to be involved in biological pathways such as DNA and chromatin activity, plant-pathogen interaction, plant hormone signal transduction, secondary metabolite biosynthesis, and defense response. Among the core-enriched genes in 12 key pathways related to resistance, 36 genotype-specific DEGs were identified. RT-qPCR integrated analysis revealed that multiple DEGs may play a significant role in tomato response to Rs. In particular, Solyc01g073985.1 (NLR disease resistance protein) and Solyc04g058170.1 (calcium-binding protein) in plant-pathogen interaction are likely to be involved in the resistance.

CONCLUSION

We analyzed the transcriptomes of both resistant and susceptible tomato lines during control and inoculated conditions and identified several key genotype-specific hub genes involved in a variety of different biological processes. These findings lay a foundation for better understanding the molecular basis by which resistant tomato lines respond to Rs.

Progress in rice sheath blight resistance research

Rice sheath blight (ShB) disease poses a major threat to rice yield throughout the world. However, the defense mechanisms against ShB in rice remain largely unknown. ShB resistance is a typical quantitative trait controlled by multiple genes. With the rapid development of molecular methods, many quantitative trait loci (QTLs) related to agronomic traits, biotic and abiotic stresses, and yield have been identified by genome-wide association studies. The interactions between plants and pathogens are controlled by various plant hormone signaling pathways, and the pathways synergistically or antagonistically interact with each other, regulating plant growth and development as well as the defense response. This review summarizes the regulatory effects of hormones including auxin, ethylene, salicylic acid, jasmonic acid, brassinosteroids, gibberellin, abscisic acid, strigolactone, and cytokinin on ShB and the crosstalk between the various hormones. Furthermore, the effects of sugar and nitrogen on rice ShB resistance, as well as information on genes related to ShB resistance in rice and their effects on ShB are also discussed. In summary, this review is a comprehensive description of the QTLs, hormones, nutrition, and other defense-related genes related to ShB in rice. The prospects of targeting the resistance mechanism as a strategy for controlling ShB in rice are also discussed.

The nuclear effector ArPEC25 from the necrotrophic fungus Ascochyta rabiei targets the chickpea transcription factor CaβLIM1a and negatively modulates lignin biosynthesis, increasing host susceptibility

Fungal pathogens deploy a barrage of secreted effectors to subvert host immunity, often by evading, disrupting, or altering key components of transcription, defense signaling, and metabolic pathways. However, the underlying mechanisms of effectors and their host targets are largely unexplored in necrotrophic fungal pathogens. Here, we describe the effector protein Ascochyta rabiei PEXEL-like Effector Candidate 25 (ArPEC25), which is secreted by the necrotroph A. rabiei, the causal agent of Ascochyta blight disease in chickpea (Cicer arietinum), and is indispensable for virulence. After entering host cells, ArPEC25 localizes to the nucleus and targets the host LIM transcription factor CaβLIM1a. CaβLIM1a is a transcriptional regulator of CaPAL1, which encodes phenylalanine ammonia lyase (PAL), the regulatory, gatekeeping enzyme of the phenylpropanoid pathway. ArPEC25 inhibits the transactivation of CaβLIM1a by interfering with its DNA-binding ability, resulting in negative regulation of the phenylpropanoid pathway and decreased levels of intermediates of lignin biosynthesis, thereby suppressing lignin production. Our findings illustrate the role of fungal effectors in enhancing virulence by targeting a key defense pathway that leads to the biosynthesis of various secondary metabolites and antifungal compounds. This study provides a template for the study of less explored necrotrophic effectors and their host target functions.

Molecular module of CmMYB15-like-Cm4CL2 regulating lignin biosynthesis of chrysanthemum (Chrysanthemum morifolium) in response to aphid (Macrosiphoniella sanborni) feeding

Lignin is a major component of plant cell walls and a conserved basic defense mechanism in higher plants deposited in response to aphid infection. However, the molecular mechanisms of lignin biosynthesis in response to aphid infection and the effect of lignin on aphid feeding behavior remain unclear. We report that 4-Coumarate:coenzyme A ligase 2 (Cm4CL2), a gene encoding a key enzyme in the lignin biosynthesis pathway, is induced by aphid feeding, resulting in lignin deposition and reduced aphid attack. Upstream regulator analysis showed that the expression of Cm4CL2 in response to aphid feeding was directly upregulated by CmMYB15-like, an SG2-type R2R3-MYB transcription factor. CmMYB15-like binds directly to the AC cis-element in the promoter region of Cm4CL2. Genetic validation demonstrated that CmMYB15-like was induced by aphid infection and contributed to lignin deposition and cell wall thickening, which consequently enhanced aphid resistance in a Cm4CL2-dependent manner. This study is the first to show that the CmMYB15-like-Cm4CL2 module regulates lignin biosynthesis in response to aphid feeding.