ABNORMAL INFLORESCENCE MERISTEM1 Functions in Salicylic Acid Biosynthesis to Maintain Proper Reactive Oxygen Species Levels for Root Meristem Activity in Rice

Rooted in Communication: Exploring Auxin-Salicylic Acid Nexus in Root Growth and Development

Plant hormones are pivotal in orchestrating diverse aspects of growth and developmental processes. Among various phytohormones, auxin and salicylic acid (SA) stand out as important regulators, often exerting opposing effects on overall plant growth. Essentially, research has indicated that auxin and SA-mediated pathways exhibit mutual antagonism during pathogen challenge. Additionally, in recent years, significant advancements have been made in uncovering the molecular intricacies that govern the action and interplay between these two phytohormones during various essential growth-related processes. In this discussion, we briefly delve into the genetic and molecular mechanisms involved in auxin and SA antagonism. We then analyse in detail how this dialogue impacts critical aspects of root development, with an emphasis on the transcriptional and protein regulatory networks. Finally, we propose the potential of exploring their interaction in various other aspects of below ground root growth processes. Understanding this relationship could provide valuable insights for optimizing and enhancing crop growth and yields.

PhWRKY30 activates salicylic acid biosynthesis to positively regulate antiviral defense response in petunia

Petunia (Petunia hybrida) plants are highly threatened by a diversity of viruses, causing substantial damage to ornamental quality and seed yield. However, the regulatory mechanism of virus resistance in petunia is largely unknown. Here, we revealed that a member of petunia WRKY transcription factors, PhWRKY30, was dramatically up-regulated following Tobacco rattle virus (TRV) infection. Down-regulation of PhWRKY30 through TRV-based virus-induced gene silencing increased green fluorescent protein (GFP)-marked TRV RNA accumulation and exacerbated the symptomatic severity. In comparison with wild-type (WT) plants, PhWRKY30-RNAi transgenic petunia plants exhibited a compromised resistance to TRV infection, whereas an enhanced resistance was observed in PhWRKY30-overexpressing (OE) transgenic plants. PhWRKY30 affected salicylic acid (SA) production and expression of arogenate dehydratase 1 (PhADT1), phenylalanine ammonia-lyase 1 (PhPAL1), PhPAL2b, nonexpressor of pathogenesis-related proteins 1 (PhNPR1), and PhPR1 in SA biosynthesis and signaling pathway. SA treatment restored the reduced TRV resistance to WT levels in PhWRKY30-RNAi plants, and application of SA biosynthesis inhibitor 2-aminoindan-2-phosphonic acid inhibited promoted resistance in PhWRKY30-OE plants. The protein-DNA binding assays showed that PhWRKY30 specifically bound to the promoter of PhPAL2b. RNAi silencing and overexpression of PhPAL2b led to decreased and increased TRV resistance, respectively. The transcription of a number of reactive oxygen species- and RNA silencing-associated genes was changed in PhWRKY30 and PhPAL2b transgenic lines. PhWRKY30 and PhPAL2b were further characterized to be involved in the resistance to Tobacco mosaic virus (TMV) invasion. Our findings demonstrate that PhWRKY30 positively regulates antiviral defense against TRV and TMV infections by modulating SA content.

The basal level of salicylic acid represses the PRT6 N-degron pathway to modulate root growth and stress response in rice

Maintaining a stable basal level of salicylic acid (SA) is crucial for plant growth, development, and stress response, although basal levels of SA vary significantly among plant species. However, the molecular mechanisms by which basal SA regulates plant growth and stress response remain to be clarified. In this study, we performed a genetic screen to identify suppressors of the root growth defect in Osaim1, a rice mutant deficient in basal SA biosynthesis. We found that mutation of the E3 ligase OsPRT6, a key component of the Arg/N-degron pathway, can rescue the root growth defect of Osaim1. Further analysis revealed that OsWRKY62 and OsWRKY76 act as substrates of the OsPRT6 N-degron pathway to modulate root growth. We demonstrated that reducing the basal SA level activates the PRT6 N-degron pathway and that basal SA modulates the stress response in part through the PRT6 N-degron pathway. Importantly, the effects of basal SA levels on the PRT6 N-degron pathway are conserved across plant species. Taken together, these findings reveal a novel regulatory mechanism by which basal SA represses the PRT6 N-degron pathway to modulate root growth and abiotic stress response in rice.

BAHD acyltransferase OsSLG mediates rice cadmium tolerance by integrating the brassinosteroid and salicylic acid pathway

Cadmium (Cd) is a highly toxic element that significantly threatens plant growth and human health. Brassinosteroids (BRs) and salicylic acid (SA) are crucial phytohormones involved in plant growth and defense. While the mechanisms by which BRs and SA individually regulate various plant biological processes have been extensively studied, their interaction with Cd in rice (Oryza sativa L.) remains poorly understood. In this study, we demonstrated that SLENDER GRAIN (OsSLG), a BR biosynthesis-related gene, plays a critical role in regulating in rice. Overexpression of OsSLG enhanced Cd tolerance, whereas OsSLG RNA interference (RNAi) lines (OsSLG-Ri) exhibited hypersensitivity to Cd stress. Exogenous BR treatment improved the Cd tolerance of the wild type and rescued the Cd-sensitive phenotype of OsSLG-Ri. Furthermore, OsSLG overexpression significantly reduced reactive oxygen species (ROS) and Cd accumulation, this reduction was attributed to the downregulation of genes involved in Cd absorption and transport, as well as the upregulation of genes associated with Cd detoxification and ROS scavenging. In addition, OsSLG enhanced the photosynthetic capacity and mineral element content in rice plants, improving their ability to cope with Cd stress. Gene expression analysis showed that OsSLG promoted the expression of the SA pathway genes, and phenotypic analysis confirmed that SA positively regulates Cd tolerance in rice. Notably, BR-induced Cd tolerance was diminished in SA biosynthesis-deficient rice plants overexpressing SA hydroxylase genes OsS5H1 and OsS5H2, suggesting that the SA pathway is necessary for BR-mediated Cd tolerance. In conclusion, our findings highlight OsSLG as a key player in elucidating the interplay between BR and SA under Cd stress.

Discovery of 4-(2-phenylethynyl) benzoic acid as a potential potent chemical pruner

Rocketing labor cost is a major challenge threatening agricultural sustainability and food security worldwide. The replacement of manual pruning of horticultural plants with chemical pruning has long been a goal for saving cost and reducing virus spreading. Here, guided by the structure-function relationship of allelochemical benzoic acid derivatives, we have identified 4-(2-phenylethynyl)-benzoicacid (PEBA) as a highly bioactive compound. PEBA arrested tomato seed germination at a concentration as low as 0.5 μM, and effectively suppressed lateral branching at 10-100 μM. In field conditions, a foliar spraying of 25 μM PEBA altered tomato plant architecture by repressing emergence and elongation of lateral buds, without significantly affecting plant growth and final fruit yield. Moreover, PEBA could also inhibit seed germination in cereals, albeit at a lower efficacy. The application of 500 μM and 750 μM PEBA profoundly curbed preharvest sprouting in wheat and rice. Acute toxicity analysis using silkworm and Trichogramma chilonis revealed that PEBA posed a low risk of toxicity. The persistence analysis further indicated that residue levels of PEBA in various plant organs were very low following applications. The inhibitory effect of PEBA on tomato seed germination was associated with the suppression of GA1 accumulation and reactive oxygen species generation, while its effect on lateral bud outgrowth were related to perturbations in the plant hormones and the modulation of genes involved in secondary metabolism and those encoding ABC transporters. Collectively, our findings demonstrate the potential of PEBA as a potent plant growth regulator with significant value for chemical pruning.

Species- and organ-specific contribution of peroxisomal cinnamate:CoA ligases to benzoic and salicylic acid biosynthesis

Salicylic acid (SA) is a prominent defense hormone whose basal level, organ-specific accumulation, and physiological role vary widely among plant species. Of the 2 known pathways of plant SA biosynthesis, the phenylalanine ammonia lyase (PAL) pathway is more ancient and universal but its biosynthetic and physiological roles in diverse plant species remain unclear. Studies in which the PAL pathway is specifically or completely inhibited, as well as a direct comparison of diverse species and different organs within the same species, are needed. To this end, we analyzed the PAL pathway in rice (Oryza sativa) and Arabidopsis (Arabidopsis thaliana), 2 distantly related model plants whose basal SA levels and distributions differ tremendously at the organism and tissue levels. Based on our recent identification of the rice peroxisomal cinnamate:CoA ligases (CNLs), we identified 2 peroxisomal CNLs from Arabidopsis and showed CNL as the most functionally specific enzyme among the known enzymes of the PAL pathway. We then revealed the species- and organ-specific contribution of the PAL pathway to benzoic and salicylic acid biosynthesis and clarified its physiological importance in rice and Arabidopsis. Our findings highlight the necessity to consider species and organ types in future SA-related studies and may help to breed new disease-resistant crops.

Peroxisomal Localization of Benzyl Alcohol O-Benzoyltransferase HSR201 is Mediated by a Non-canonical Peroxisomal Targeting Signal and Required for Salicylic Acid Biosynthesis

The phytohormone salicylic acid (SA) regulates plant responses to various types of environmental stress, particularly pathogen infections. We previously revealed that the benzyl alcohol O-benzoyltransferase HSR201 was required for pathogen signal-induced SA synthesis, and its overexpression together with NtCNL, encoding a cinnamate-coenzyme A ligase, was sufficient for the production of significant amounts of SA in tobacco. We herein examined the subcellular localization of HSR201 and found that it fused to a yellow fluorescent protein localized in peroxisomes. Most peroxisomal matrix proteins possess peroxisomal targeting signal type-1 (PTS1) located at the extreme C-terminus or PTS2 located at the N-terminus; however, a bioinformatics analysis failed to identify similar signals for HSR201. Deletion and mutation analyses of HSR201 identified one essential (extreme C-terminal Leu460) and three important (Ile455, Ile456 and Ala459) amino acid residues for its peroxisomal localization. The virus-induced gene silencing (VIGS) of PEX5, a PTS1 receptor, but not PEX7, a PTS2 receptor, compromised the peroxisomal targeting of HSR201 in Nicotiana benthamiana. When overexpressed with NtCNL, HSR201 mutants with reduced or non-peroxisomal targeting induced lower SA levels than the wild type; however, these mutations did not affect the protein stability or activity of HSR201. VIGS of the HSR201 homolog compromised pathogen signal-induced SA accumulation in N. benthamiana, which was complemented by the HSR201 wild type, but not the mutant with non-peroxisomal targeting. These results suggest that the peroxisomal localization of HSR201 is mediated by a non-canonical PTS1 and required for SA biosynthesis.

Isochorismate synthase is required for phylloquinone, but not salicylic acid biosynthesis in rice

Salicylic acid (SA) is a phytohormone required for plant growth and defense signaling. There are two major SA biosynthesis pathways in plants: the isochorismate synthase (ICS) pathway and the phenylalanine ammonia-lyase (PAL) pathway. It has been demonstrated in several plant species, including the model plant Arabidopsis, that SA is derived predominantly from the ICS pathway. Here, we employed the CRISPR/Cas9 system to generate ICS knockout mutants in rice (Oryza sativa L.). The Osics mutants display severe growth defects, and are completely devoid of phylloquinone, an isochorismate-derived product. The growth defects of Osics can be rescued through exogenous application of 1,4-dihydroxy-2-naphthoic acid (NA), a precursor of phylloquinone. Remarkably, the basal SA levels are not altered in the Osics mutants. Our findings support a role of OsICS in the biosynthesis of phylloquinone, and imply that SA biosynthesis in rice may occur through an alternative route other than the ICS pathway.

Supplementary Information

The online version contains supplementary material available at 10.1007/s42994-024-00166-4.

Molecular mechanisms underlying the effects of antibiotics on the growth and development of green tide algae Ulva prolifera

Different types of algae exhibit varied sensitivities to antibiotics, influencing their growth by eradicating epiphytic bacteria. This study explored the impact of co-culturing neomycin sulfate, polymyxin B, and penicillin G on the growth and development of Ulva prolifera gametophytes. The findings revealed a significant influence of antibiotics on the morphology, growth, chlorophyll fluorescence parameters, and CAT activity of U. prolifera. The 16S rDNA sequencing revealed a significant decrease in the abundance of Maribacter spp. after antibiotic treatment of U. prolifera. Antibiotic treatment caused up-regulation of genes related to cellulose synthase, tubulin, and ribosomal protein. Conversely, key genes in the DNA replication pathway, such as mcm and Polε, were down-regulated, influencing cell division and resulting in irregular algal shapes. The up-regulation of enzyme genes in the C3 and C4 pathways, CAT, and drug metabolism genes enhanced the antioxidant and photosynthetic capacities of U. prolifera, providing a certain resilience to stress.

Transcription-Aided Selection (TAS) for Crop Disease Resistance: Strategy and Evidence

A transcription-aided selection (TAS) strategy is proposed in this paper, which utilizes the positive regulatory roles of genes involved in the plant immunity pathways to screen crops with high disease resistance. Increased evidence has demonstrated that upon pathogen attack, the expression of diverse genes involved in salicylic acid (SA)-mediated SAR are differentially expressed and transcriptionally regulated. The paper discusses the molecular mechanisms of the SA signaling pathway, which plays a central role in plant immunity, and identifies differentially expressed genes (DEGs) that could be targeted for transcriptional detection. We have conducted a series of experiments to test the TAS strategy and found that the level of GmSAGT1 expression is highly correlated with soybean downy mildew (SDM) resistance with a correlation coefficient R2 = 0.7981. Using RT-PCR, we screened 2501 soybean germplasms and selected 26 collections with higher levels of both GmSAGT1 and GmPR1 (Pathogenesis-related proteins1) gene expression. Twenty-three out of the twenty-six lines were inoculated with Peronospora manshurica (Pm) in a greenhouse. Eight showed HR (highly resistant), four were R (resistant), five were MR (moderately resistant), three were S (susceptible), and three were HS (highly susceptible). The correlation coefficient R2 between the TAS result and Pm inoculation results was 0.7035, indicating a satisfactory consistency. The authors anticipate that TAS provides an effective strategy for screening crops with broad-spectrum and long-lasting resistance.

Genome-wide association study (GWAS) analyses of early anatomical changes in rose adventitious root formation

Adventitious root (AR) formation is a genetically complex trait with high genotypic variability. Therefore, only a limited range of cultivars are currently propagated by cuttings in rose. In this study, we analysed the anatomy of in vitro shoots, the early formation of root primordia (RP) and the formation of ARs in a diverse set of 106 rose genotypes. Correlation analysis indicated that the growth in shoot diameter and the vasculature dimensions after 1 week of rooting contributed to successful AR formation. Using phenotypic data for genome-wide association studies (GWAS) analyses, nine significantly associated single nucleotide polymorphisms (SNPs) and genomic regions contributing to various RP and AR formation traits were identified. The contribution of genomic regions to trait variation was notably greater for traits associated with earlier processes than for traits associated with later developmental stages. The combination of RP and AR data allowed the detection of regions by GWAS that contain factors that potentially limit RP emergence. Homologues of 47 genes known to be involved in AR formation from the literature could be assigned to the identified peaks. Further studies are needed to investigate the suitability of SNPs exhibiting strong effects as allele-specific PCR markers for use in breeding.

Effects of acetic acid fermentation product and its components on defense signaling in rice

Acetic acid fermentation product made from isomalto-oligosaccharide as the main raw material is composed of isomalto-oligosaccharide and acetic acid. In this paper, we have shown that the fermentation product enhanced the expression of disease resistance genes in rice, and that its main functional component was acetic acid. It has been reported so far that acetic acid enhances the jasmonic acid signaling pathway, while the role of isomalto-oligosaccharide in plant defense signaling remains unclear. In this study, we demonstrated the possibility that isomalto-oligosaccharide shifted part of the jasmonic acid signaling pathway, which is enhanced by acetic acid, to the salicylic acid signaling pathway, which is the other major defense pathway. Furthermore, glucose, a constituent monosaccharide of isomalto-oligosaccharide, and a disaccharide maltose had little effect on the signaling pathway, but a trisaccharide maltotriose tended to have a similar effect to isomalto-oligosaccharide on the defense signaling pathway.

Structural basis of chorismate isomerization by Arabidopsis ISOCHORISMATE SYNTHASE1

Salicylic acid (SA) plays a crucial role in plant defense against biotrophic and semibiotrophic pathogens. In Arabidopsis (Arabidopsis thaliana), isochorismate synthase 1 (AtICS1) is a key enzyme for the pathogen-induced biosynthesis of SA via catalytic conversion of chorismate into isochorismate, an essential precursor for SA synthesis. Despite the extensive knowledge of ICS1-related menaquinone, siderophore, and tryptophan (MST) enzymes in bacteria, the structural mechanisms for substrate binding and catalysis in plant isochorismate synthase (ICS) enzymes are unknown. This study reveals that plant ICS enzymes catalyze the isomerization of chorismate through a magnesium-dependent mechanism, with AtICS1 exhibiting the most substantial catalytic activity. Additionally, we present high-resolution crystal structures of apo AtICS1 and its complex with chorismate, offering detailed insights into the mechanisms of substrate recognition and catalysis. Importantly, our investigation indicates the existence of a potential substrate entrance channel and a gating mechanism regulating substrate into the catalytic site. Structural comparisons of AtICS1 with MST enzymes suggest a shared structural framework with conserved gating and catalytic mechanisms. This work provides valuable insights into the structural and regulatory mechanisms governing substrate delivery and catalysis in AtICS1, as well as other plant ICS enzymes.

Evolution of reactive oxygen species cellular targets for plant development

Reactive oxygen species (ROS) are the key players in regulating developmental processes of plants. Plants have evolved a large array of gene families to facilitate the ROS-regulated developmental process in roots and leaves. However, the cellular targets of ROS during plant evolutionary development are still elusive. Here, we found early evolution and large expansions of protein families such as mitogen-activated protein kinases (MAPK) in the evolutionarily important plant lineages. We review the recent advances in interactions among ROS, phytohormones, gasotransmitters, and protein kinases. We propose that these signaling molecules act in concert to maintain cellular ROS homeostasis in developmental processes of root and leaf to ensure the fine-tuning of plant growth for better adaptation to the changing climate.

Ontogenic stage-associated SA response contributes to leaf age-dependent resistance in Arabidopsis and cotton

Introduction

As leaves grow, they transition from a low-microbe environment embedded in shoot apex to a more complex one exposed to phyllosphere microbiomes. Such change requires a coordinated reprogramming of cellular responses to biotic stresses. It remains unclear how plants shift from fast growth to robust resistance during organ development.

Results

Here, we reported that salicylic acid (SA) accumulation and response were temporarily increased during leaf maturation in herbaceous annual Arabidopsis. Leaf primordia undergoing active cell division were insensitive to the elicitor-induced SA response. This age-dependent increase in SA response was not due to prolonged exposure to environmental microbes. Autoimmune mutants with elevated SA levels did not alter the temporal pattern dependent on ontogenic stage. Young Arabidopsis leaves were more susceptible than mature leaves to Pseudomonas syringae pv. tomato (Pto) DC3000 cor- infection. Finally, we showed a broadly similar pattern in cotton, a woody perennial, where young leaves with reduced SA signaling were preferentially invaded by a Xanthomonas pathogen after leaf surface infection.

Discussion

Through this work, we provided insights in the SA-mediated ontogenic resistance in Arabidopsis and tomato.

The genetic orchestra of salicylic acid in plant resilience to climate change induced abiotic stress: critical review

Climate change, driven by human activities and natural processes, has led to critical alterations in varying patterns during cropping seasons and is a vital threat to global food security. The climate change impose several abiotic stresses on crop production systems. These abiotic stresses include extreme temperatures, drought, and salinity, which expose agricultural fields to more vulnerable conditions and lead to substantial crop yield and quality losses. Plant hormones, especially salicylic acid (SA), has crucial roles for plant resiliency under unfavorable environments. This review explores the genetics and molecular mechanisms underlying SA's role in mitigating abiotic stress-induced damage in plants. It also explores the SA biosynthesis pathways, and highlights the regulation of their products under several abiotic stresses. Various roles and possible modes of action of SA in mitigating abiotic stresses are discussed, along with unraveling the genetic mechanisms and genes involved in responses under stress conditions. Additionally, this review investigates molecular pathways and mechanisms through which SA exerts its protective effects, such as redox signaling, cross-talks with other plant hormones, and mitogen-activated protein kinase pathways. Moreover, the review discusses potentials of using genetic engineering approaches, such as CRISPR technology, for deciphering the roles of SA in enhancing plant resilience to climate change related abiotic stresses. This comprehensive analysis bridges the gap between genetics of SA role in response to climate change related stressors. Overall goal is to highlight SA's significance in safeguarding plants and by offering insights of SA hormone for sustainable agriculture under challenging environmental conditions.

A peroxisomal cinnamate:CoA ligase-dependent phytohormone metabolic cascade in submerged rice germination

The mechanism underlying the ability of rice to germinate underwater is a largely enigmatic but key research question highly relevant to rice cultivation. Moreover, although rice is known to accumulate salicylic acid (SA), SA biosynthesis is poorly defined, and its role in underwater germination is unknown. It is also unclear whether peroxisomes, organelles essential to oilseed germination and rice SA accumulation, play a role in rice germination. Here, we show that submerged imbibition of rice seeds induces SA accumulation to promote germination in submergence. Two submergence-induced peroxisomal Oryza sativa cinnamate:CoA ligases (OsCNLs) are required for this SA accumulation. SA exerts this germination-promoting function by inducing indole-acetic acid (IAA) catabolism through the IAA-amino acid conjugating enzyme GH3. The metabolic cascade we identified may potentially be adopted in agriculture to improve the underwater germination of submergence-intolerant rice varieties. SA pretreatment is also a promising strategy to improve submerged rice germination in the field.

The Slow Growth of Adventitious Roots in Tetraploid Hybrid Poplar (Populus simonii × P. nigra var. italica) May Be Caused by Endogenous Hormone-Mediated Meristem Shortening

Polyploidization produces abundant phenotypic variation. Little is currently known about adventitious root (AR) development variation due to polyploidization. In this study, we analyzed the morphological, cytological, and physiological variations in AR development between tetraploid and diploid Populus plants during in vitro rooting culture. Compared to the diploids, the AR formation times and rooting rates of the tetraploids' stem explants had non-significant changes. However, the tetraploid ARs exhibited significantly slower elongation growth than the diploid ARs. Cytological observation showed that the tetraploid ARs were characterized by shorter root meristems and reduced meristem cell numbers, suggesting the reasons for the slow AR elongation. Analysis of hormones and related metabolites during AR development demonstrated that the total auxin, cytokinin, and jasmonic acid contents were significantly lower in the tetraploid ARs than in those of the diploids, and that the ratio of total auxins to total CKs at 0 h of AR development was also lower in the tetraploids than in the diploids, whereas the total salicylic acid content of the tetraploids was consistently higher than that of the diploids. qPCR analysis showed that the expression levels of several hormone signaling and cell division-related genes in the tetraploid ARs significantly differed from those in the diploids. In conclusion, the slow elongation of the tetraploid ARs may be caused by the endogenous hormone-mediated meristem shortening. Our findings enhance the understanding of polyploidization-induced variation in AR development of forest trees.

Decoding the molecular mechanism underlying salicylic acid (SA)-mediated plant immunity: an integrated overview from its biosynthesis to the mode of action

Salicylic acid (SA) is an important phytohormone, well-known for its regulatory role in shaping plant immune responses. In recent years, significant progress has been made in unravelling the molecular mechanisms underlying SA biosynthesis, perception, and downstream signalling cascades. Through the concerted efforts employing genetic, biochemical, and omics approaches, our understanding of SA-mediated defence responses has undergone remarkable expansion. In general, following SA biosynthesis through Avr effectors of the pathogens, newly synthesized SA undergoes various biochemical changes to achieve its active/inactive forms (e.g. methyl salicylate). The activated SA subsequently triggers signalling pathways associated with the perception of pathogen-derived signals, expression of defence genes, and induction of systemic acquired resistance (SAR) to tailor the intricate regulatory networks that coordinate plant immune responses. Nonetheless, the mechanistic understanding of SA-mediated plant immune regulation is currently limited because of its crosstalk with other signalling networks, which makes understanding this hormone signalling more challenging. This comprehensive review aims to provide an integrated overview of SA-mediated plant immunity, deriving current knowledge from diverse research outcomes. Through the integration of case studies, experimental evidence, and emerging trends, this review offers insights into the regulatory mechanisms governing SA-mediated immunity and signalling. Additionally, this review discusses the potential applications of SA-mediated defence strategies in crop improvement, disease management, and sustainable agricultural practices.

Cassava phosphatase PP2C1 modulates thermotolerance via fine-tuning dephosphorylation of antioxidant enzymes

Global warming is an adverse environmental factor that threatens crop yields and food security. 2C-type protein phosphatases (PP2Cs), as core protein phosphatase components, play important roles in plant hormone signaling to cope with various environmental stresses. However, the function and underlying mechanism of PP2Cs in the heat stress response remain elusive in tropical crops. Here, we report that MePP2C1 negatively regulated thermotolerance in cassava (Manihot esculenta Crantz), accompanied by the modulation of reactive oxygen species (ROS) accumulation and the underlying antioxidant enzyme activities of catalase (CAT) and ascorbate peroxidase (APX). Further investigation found that MePP2C1 directly interacted with and dephosphorylated MeCAT1 and MeAPX2 at serine (S) 112 and S160 residues, respectively. Moreover, in vitro and in vivo assays showed that protein phosphorylation of MeCAT1S112 and MeAPX2S160 was essential for their enzyme activities, and MePP2C1 negatively regulated thermotolerance and redox homeostasis by dephosphorylating MeCAT1S112 and MeAPX2S160. Taken together, this study illustrates the direct relationship between MePP2C1-mediated protein dephosphorylation of MeCAT1 and MeAPX2 and ROS accumulation in thermotolerance to provide insights for adapting to global warming via fine-tuning thermotolerance of the tropical crop cassava.

Evaluation of Virus-Free Chrysanthemum 'Hangju' Productivity and Response to Virus Reinfection in the Field: Molecular Insights into Virus-Host Interactions

The shoot apical meristem culture has been used widely to produce virus-free plantlets which have the advantages of strong disease resistance, high yield, and prosperous growth potential. However, this virus-free plant will be naturally reinfected in the field. The physiological and metabolic responses in the reinfected plant are still unknown. The flower of chrysanthemum 'Hangju' is a traditional medicine which is unique to China. In this study, we found that the virus-free 'Hangju' (VFH) was reinfected with chrysanthemum virus B/R in the field. However, the reinfected VFH (RVFH) exhibited an increased yield and medicinal components compared with virus-infected 'Hangju' (VIH). Comparative analysis of transcriptomes was performed to explore the molecular response mechanisms of the RVFH to CVB infection. A total of 6223 differentially expressed genes (DEGs) were identified in the RVFH vs. the VIH. KEGG enrichment and physiological analyses indicated that treatment with the virus-free technology significantly mitigated the plants' lipid and galactose metabolic stress responses in the RVFH. Furthermore, GO enrichment showed that plant viral diseases affected salicylic acid (SA)-related processes in the RVFH. Specifically, we found that phenylalanine ammonia-lyase (PAL) genes played a major role in defense-related SA biosynthesis in 'Hangju'. These findings provided new insights into the molecular mechanisms underlying plant virus-host interactions and have implications for developing strategies to improve plant resistance against viruses.

Biochemical Pathways of Salicylic Acid Derived from l-Phenylalanine in Plants with Different Basal SA Levels

As a plant hormone, salicylic acid (SA) has diverse regulatory roles in plant growth and stress resistance. Although SA is widely found in plants, there is substantial variation in basal SA among species. Tea plant is an economically important crop containing high contents of SA whose synthesis pathway remains unidentified. The phenylalanine ammonia-lyase (PAL) pathway is responsible for basal SA synthesis in plants. In this study, isotopic tracing and enzymatic assay experiments were used to verify the SA synthesis pathway in tea plants and evaluate the variation in phenylalanine-derived SA formation among 11 plant species with different levels of SA. The results indicated that SA could be synthesized via PAL in tea plants and conversion efficiency from benzoic acid to SA might account for variation in basal SA among plant species. This research lays the foundation for an improved understanding of the molecular regulatory mechanism for SA biosynthesis.

The hidden harmony: Exploring ROS-phytohormone nexus for shaping plant root architecture in response to environmental cues

Root system architecture, encompassing lateral roots and root hairs, plays a vital in overall plant growth and stress tolerance. Reactive oxygen species (ROS) and plant hormones intricately regulate root growth and development, serving as signaling molecules that govern processes such as cell proliferation and differentiation. Manipulating the interplay between ROS and hormones has the potential to enhance nutrient absorption, stress tolerance, and agricultural productivity. In this review, we delve into how studying these processes provides insights into how plants respond to environmental changes and optimize growth patterns to better control cellular processes and stress responses in crops. We discuss various factors and complex signaling networks that may exist among ROS and phytohormones during root development. Additionally, the review highlights possible role of reactive nitrogen species (RNS) in ROS-phytohormone interactions and in shaping root system architecture according to environmental cues.

MAP kinases may mediate regulation of the cell cycle in rice by E2F2 phosphorylation

E2F is the key transcription factor that determines the proliferative status of cells by regulating the G1/S phase of the cell cycle. In this study, we show that in rice (Oryza sativa), OsE2F2 is a phosphorylation target of MAP kinases. The MAP kinases OsMPK3, OsMPK4, and OsMPK6 interact with and phosphorylate OsE2F2. Next, we determined the serine and threonine residues that could play a role in the phosphorylation of OsE2F2. Subsequently, our study suggests a possible link between MAP kinase-mediated OsE2F2 phosphorylation and its impact on DNA proliferation in the roots of rice seedlings. Finally, we found positive feedback regulation of OsMPK4 by OsE2F2. Therefore, our study hints at the potential impact of MAP kinase signaling on the cell cycle of rice plants.

TFIIB-Related Protein BRP5/PTF2 Is Required for Both Male and Female Gametogenesis and for Grain Formation in Rice

Transcription factor IIB (TFIIB) is a general transcription factor for RNA polymerase II, exerting its influence across various biological contexts. In the majority of eukaryotes, TFIIB typically has two homologs, serving as general transcription factors for RNA polymerase I and III. In plants, however, the TFIIB-related protein family has expanded greatly, with 14 and 9 members in Arabidopsis and rice, respectively. BRP5/pollen-expressed transcription factor 2 (PTF2) proteins belong to a subfamily of TFIIB-related proteins found only in plants and algae. The prior analysis of an Arabidopsis atbrp5 mutant, characterized by a T-DNA insertion at the 5' untranslated region, demonstrated the essential role of BRP5/PTF2 during the process of pollen germination and embryogenesis in Arabidopsis. Using a rice transformation system based on CRISPR/Cas9 technology, we have generated transgenic rice plants containing loss-of-function frameshift mutations in the BRP5/PTF2 gene. Unlike in the Arabidopsis atbrp5 mutant, the brp5/ptf2 frameshift mutations were not transmitted to progeny in rice, indicating an essential role of BRP5/PTF2 in both male and female gamete development or viability. The silencing of rice BRP5/PTF2 expression through RNA interference (RNAi) had little effect on vegetative growth and panicle formation but strongly affected pollen development and grain formation. Genetic analysis revealed that strong RNAi silencing of rice BRP5/PTF2 was still transmissible to progeny almost exclusively through female gametes, as found in the Arabidopsis atbrp5 knockdown mutant. Thus, reduced rice BRP5/PTF2 expression impacted pollen preferentially by interfering with male gamete development or viability. Drawing upon these findings, we posit that BRP5/PTF2 assumes a distinct and imperative function in the realm of plant sexual reproduction.

The miRNA-mRNA regulatory networks of the response to NaHCO3 stress in industrial hemp (Cannabis sativa L.)

BACKGROUND

Industrial hemp is an important industrial crop and has strong resistance to saline-alkaline stress. However, research on the industrial hemp response to NaHCO3 stress is limited. Therefore, the response mechanisms of industrial hemp under NaHCO3 stress were analysed through miRNA-mRNA regulatory networks.

RESULTS

Seedlings of two salt-alkali tolerant and sensitive varieties were cultured in a solution containing 100 mM NaHCO3 and randomly sampled at 0, 6, 12, and 24 h. With prolonged NaHCO3 stress, the seedlings gradually withered, and the contents of jasmonic acid, lignin, trehalose, soluble protein, peroxidase, and superoxide dismutase in the roots increased significantly. The abscisic acid content decreased and then gradually increased. Overall, 18,215 mRNAs and 74 miRNAs were identified as differentially expressed under NaHCO3 stress. The network showed that 230 miRNA-mRNA interactions involved 16 miRNAs and 179 mRNAs, including some key hub novel mRNAs of these crucial pathways. Carbon metabolism, starch, sucrose metabolism, plant hormone signal transduction, and the spliceosome (SPL) were crucial pathways in industrial hemp's response to NaHCO3 stress.

CONCLUSIONS

It is speculated that industrial hemp can regulate SPL pathway by upregulating miRNAs such as novel_miR_179 and novel_miR_75, thus affecting starch and sucrose metabolism, plant hormone signal transduction and carbon metabolism and improving key physiological indices such as jasmonic acid content, trehalose content, and peroxidase and superoxide dismutase activities under NaHCO3 stress.

ROS: Important factor in plant stem cell fate regulation

Reactive oxygen species (ROS) are initially considered to be toxic byproducts of aerobic metabolic reactions. However, increasing evidence has shown that they have emerged as signaling molecules involved in several basic biological processes. Recent studies highlight the pivotal role of ROS in the maintenance of shoot and root stem cell niche. In this review, we discuss the impact of ROS distribution and their gradients on the stability of the stem cell niches (SCN) in shoot apical meristem (SAM) and root apical meristem (RAM) by determining the balance between stemness and differentiation. We also summarize several important transcription factors that are involved in the regulation of ROS balance in SAM and RAM, regulating key enzymes in ROS metabolism, especially SOD and peroxidase. ROS are also tightly interconnected with phytohormones in the control of the stem cell fate. Besides, ROS are also important regulators of the cell cycle in controlling the size of the stem cells. Understanding the regulation mechanisms of ROS production, polarization gradient distribution, homeostasis, and downstream signal transduction in cells will open exciting new perspectives for plant developmental biology.

CRISPR/Cas9-mediated simultaneous mutation of three salicylic acid 5-hydroxylase (OsS5H) genes confers broad-spectrum disease resistance in rice

Salicylic acid (SA) is an essential plant hormone that plays critical roles in basal defence and amplification of local immune responses and establishes resistance against various pathogens. However, the comprehensive knowledge of the salicylic acid 5-hydroxylase (S5H) in rice-pathogen interaction is still elusive. Here, we reported that three OsS5H homologues displayed salicylic acid 5-hydroxylase activity, converting SA into 2,5-dihydroxybenzoic acid (2,5-DHBA). OsS5H1, OsS5H2, and OsS5H3 were preferentially expressed in rice leaves at heading stage and responded quickly to exogenous SA treatment. We found that bacterial pathogen Xanthomonas oryzae pv. oryzae (Xoo) strongly induced the expression of OsS5H1, OsS5H2, and OsS5H3. Rice plants overexpressing OsS5H1, OsS5H2, and OsS5H3 showed significantly decreased SA contents and increased 2,5-DHBA levels, and were more susceptible to bacterial blight and rice blast. A simple single guide RNA (sgRNA) was designed to create oss5h1oss5h2oss5h3 triple mutants through CRISPR/Cas9-mediated gene mutagenesis. The oss5h1oss5h2oss5h3 exhibited stronger resistance to Xoo than single oss5h mutants. And oss5h1oss5h2oss5h3 plants displayed enhanced rice blast resistance. The conferred pathogen resistance in oss5h1oss5h2oss5h3 was attributed to the significantly upregulation of OsWRKY45 and pathogenesis-related (PR) genes. Besides, flg22-induced reactive oxygen species (ROS) burst was enhanced in oss5h1oss5h2oss5h3. Collectively, our study provides a fast and effective approach to generate rice varieties with broad-spectrum disease resistance through OsS5H gene editing.

Salicylate and jasmonate intertwine in ROS-triggered chloroplast-to-nucleus retrograde signaling

Plants, being sessile, are frequently exposed to environmental perturbations, affecting their sustenance and survival. In response, distinct inherent mechanisms emerged during plant evolution to deal with environmental stresses. Among various organelles, chloroplast plays an indispensable role in plant cells. Besides providing the site for photosynthesis and biosynthesis of many important primary and secondary metabolites, including hormones, chloroplasts also act as environmental sensors. Any environmental perturbation directly influences the photosynthetic electron transport chain, leading to excess accumulation of reactive oxygen species (ROS), causing oxidative damages to biomolecules in the vicinity. To prevent excess ROS accumulation and the consequent oxidative damages, the chloroplast activates retrograde signaling (RS) pathways to reprogramme nuclear gene expression, defining plant's response to stress. Based on levels and site of ROS accumulation, distinct biomolecules are oxidized, generating specific derivatives that act as genuine signaling molecules, triggering specific RS pathways to instigate distinctive responses, including growth inhibition, acclimation, and programmed cell death. Though various RS pathways independently modulate nuclear gene expression, they also implicate the defense hormone salicylic acid (SA) and oxylipins, including 12-oxo-phytodienoic acid (OPDA) and jasmonic acid (JA), by promoting their biosynthesis and utilizing them for intra- and intercellular communications. Several studies reported the involvement of both hormones in individual RS pathways, but the precise dissection of their activation and participation in a given RS pathway remains an enigma. The present review describes the current understanding of how SA and JA intertwine in ROS-triggered RS pathways. We have also emphasized the future perspectives for elucidating stress specificity and spatiotemporal accumulation of respective hormones in a given RS pathway.

Functions of WRKYs in plant growth and development

As sessile organisms, plants must overcome various stresses. Accordingly, they have evolved several plant-specific growth and developmental processes. These plant processes may be related to the evolution of plant-specific protein families. The WRKY transcription factors originated in eukaryotes and expanded in plants, but are not present in animals. Over the past two decades, there have been many studies on WRKYs in plants, with much of the research concentrated on their roles in stress responses. Nevertheless, recent findings have revealed that WRKYs are also required for seed dormancy and germination, postembryonic morphogenesis, flowering, gametophyte development, and seed production. Thus, WRKYs may be important for plant adaptations to a sessile lifestyle because they simultaneously regulate stress resistance and plant-specific growth and development.

The SMC5/6 complex subunit MMS21 regulates stem cell proliferation in rice

KEY MESSAGE

SMC5/6 complex subunit OsMMS21 is involved in cell cycle and hormone signaling and required for stem cell proliferation during shoot and root development in rice. The structural maintenance of chromosome (SMC)5/6 complex is required for nucleolar integrity and DNA metabolism. Moreover, METHYL METHANESULFONATE SENSITIVITY GENE 21 (MMS21), a SUMO E3 ligase that is part of the SMC5/6 complex, is essential for the root stem cell niche and cell cycle transition in Arabidopsis. However, its specific role in rice remains unclear. Here, OsSMC5 and OsSMC6 single heterozygous mutants were generated using CRISPR/Cas9 technology to elucidate the function of SMC5/6 subunits, including OsSMC5, OsSMC6, and OsMMS21, in cell proliferation in rice. ossmc5/ + and ossmc6/ + heterozygous single mutants did not yield homozygous mutants in their progeny, indicating that OsSMC5 and OsSMC6 both play necessary roles during embryo formation. Loss of OsMMS21 caused severe defects in both the shoot and roots in rice. Transcriptome analysis showed a significant decrease in the expression of genes involved in auxin signaling in the roots of osmms21 mutants. Moreover, the expression levels of the cycB2-1 and MCM genes, which are involved the cell cycle, were significantly lower in the shoots of the mutants, indicating that OsMMS21 was involved in both hormone signaling pathways and the cell cycle. Overall, these findings indicate that the SUMO E3 ligase OsMMS21 is required for both shoot and root stem cell niches, improving the understanding of the function of the SMC5/6 complex in rice.

AIM1-dependent high basal salicylic acid accumulation modulates stomatal aperture in rice

The basal levels of salicylic acid (SA) vary dramatically among plant species. In the shoot, for example, rice contains almost 100 times higher SA levels than Arabidopsis. Despite its high basal levels, neither the biosynthetic pathway nor the biological functions of SA are well understood in rice. Combining with metabolite analysis, physiological, and genetic approaches, we found that the synthesis of basal SA in rice shoot is dependent on OsAIM1, which encodes a beta-oxidation enzyme in the phenylalanine ammonia-lyase (PAL) pathway. Compromised SA accumulation in the Osaim1 mutant led to a lower shoot temperature than wild-type plants. However, this shoot temperature defect resulted from increased transpiration due to elevated steady-state stomatal aperture in the mutant. Furthermore, the high basal SA level is required for sustained expression of OsWRKY45 to modulate the steady-state stomatal aperture and shoot temperature in rice. Taken together, these results provide the direct genetic evidence for the critical role of the PAL pathway in the biosynthesis of high basal level SA in rice, which plays an important role in the regulation of steady-state stomatal aperture to promote fitness under stress conditions.

OsMBTB32, a MATH-BTB domain-containing protein that interacts with OsCUL1s to regulate salt tolerance in rice

MATH-BTB proteins are involved in a variety of cellular processes that regulate cell homeostasis and developmental processes. Previous studies reported the involvement of BTB proteins in the development of various organs in plants; however, the function of BTB proteins in salt stress is less studied. Here, we found a novel MATH-BTB domain-containing OsMBTB32 protein that was highly expressed in leaf, root, and shoot. The up-regulation of the OsMBTB32 transcript in 2-week-old seedlings under salt stress suggests the significant role of the OsMBTB32 gene in salinity. The OsMBTB32 transgenic seedlings (OE and RNAi) exhibited significant differences in various phenotypes, including plumule, radical, primary root, and shoot length, compared to WT seedlings. We further found that OsCUL1 proteins, particularly OsCUL1-1 and OsCUL1-3, interact with OsMBTB32 and may suppress the function of OsMBTB32 during salt stress. Moreover, OsWRKY42, a homolog of ZmWRKY114 which negatively regulates salt stress in rice, directly binds to the W-box of OsCUL1-1 and OsCUL1-3 promoters to promote the interaction of OsCUL1-1 and OsCUL1-3 with OsMBTB32 protein in rice. The overexpression of OsMBTB32 and OsCUL1-3 further confirmed the function of OsMBTB32 and OsCUL1s in salt tolerance in Arabidopsis. Overall, the findings of the present study provide promising knowledge regarding the MATH-BTB domain-containing proteins and their role in enhancing the growth and development of rice under salt stress.MATH-BTB proteins are involved in a variety of cellular processes that regulate cell homeostasis and developmental processes. Previous studies reported the involvement of BTB proteins in the development of various organs in plants; however, the function of BTB proteins in salt stress is less studied. Here, we found a novel MATH-BTB domain-containing OsMBTB32 protein that was highly expressed in leaf, root, and shoot. The up-regulation of the OsMBTB32 transcript in 2-week-old seedlings under salt stress suggests the significant role of the OsMBTB32 gene in salinity. The OsMBTB32 transgenic seedlings (OE and RNAi) exhibited significant differences in various phenotypes, including plumule, radical, primary root, and shoot length, compared to WT seedlings. We further found that OsCUL1 proteins, particularly OsCUL1-1 and OsCUL1-3, interact with OsMBTB32 and may suppress the function of OsMBTB32 during salt stress. Moreover, OsWRKY42, a homolog of ZmWRKY114 which negatively regulates salt stress in rice, directly binds to the W-box of OsCUL1-1 and OsCUL1-3 promoters to promote the interaction of OsCUL1-1 and OsCUL1-3 with OsMBTB32 protein in rice. The overexpression of OsMBTB32 and OsCUL1-3 further confirmed the function of OsMBTB32 and OsCUL1s in salt tolerance in Arabidopsis. Overall, the findings of the present study provide promising knowledge regarding the MATH-BTB domain-containing proteins and their role in enhancing the growth and development of rice under salt stress.

The Peroxisomal β-Oxidative Pathway and Benzyl Alcohol O-Benzoyltransferase HSR201 Cooperatively Contribute to the Biosynthesis of Salicylic Acid

The phytohormone salicylic acid (SA) regulates plant defense responses against pathogens. Previous studies have suggested that SA is mainly produced from trans-cinnamic acid (CA) in tobacco, but the underlying mechanisms remain largely unknown. SA synthesis is activated by wounding in tobacco plants in which the expression of WIPK and SIPK, two mitogen-activated protein kinases, is suppressed. Using this phenomenon, we previously revealed that HSR201 encoding benzyl alcohol O-benzoyltransferase is required for pathogen signal-induced SA synthesis. In this study, we further analyzed the transcriptomes of wounded WIPK/SIPK-suppressed plants and found that the expression of NtCNL, NtCHD and NtKAT1, homologous to cinnamate-coenzyme A (CoA) ligase (CNL), cinnamoyl-CoA hydratase/dehydrogenase (CHD) and 3-ketoacyl-CoA thiolase (KAT), respectively, is associated with SA biosynthesis. CNL, CHD and KAT constitute a β-oxidative pathway in the peroxisomes and produce benzoyl-CoA, a precursor of benzenoid compounds in petunia flowers. Subcellular localization analysis showed that NtCNL, NtCHD and NtKAT1 localize in the peroxisomes. Recombinant NtCNL catalyzed the formation of CoA esters of CA, whereas recombinant NtCHD and NtKAT1 proteins converted cinnamoyl-CoA to benzoyl-CoA, a substrate of HSR201. Virus-induced gene silencing of any one of NtCNL, NtCHD and NtKAT1 homologs compromised SA accumulation induced by a pathogen-derived elicitor in Nicotiana benthamiana leaves. Transient overexpression of NtCNL in N. benthamiana leaves resulted in SA accumulation, which was enhanced by co-expression of HSR201, although overexpression of HSR201 alone did not cause SA accumulation. These results suggested that the peroxisomal β-oxidative pathway and HSR201 cooperatively contribute to SA biosynthesis in tobacco and N. benthamiana.

Exogenous application of salicylic acid improves freezing stress tolerance in alfalfa

Freezing stress is one of the most detrimental environmental factors that can seriously impact the growth, development, and distribution of alfalfa (Medicago sativa L.). Exogenous salicylic acid (SA) has been revealed as a cost-effective method of improving defense against freezing stress due to its predominant role in biotic and abiotic stress resistance. However, how the molecular mechanisms of SA improve freezing stress resistance in alfalfa is still unclear. Therefore, in this study, we used leaf samples of alfalfa seedlings pretreatment with 200 μM and 0 μM SA, which were exposed to freezing stress (-10°C) for 0, 0.5, 1, and 2h and allowed to recover at normal temperature in a growth chamber for 2 days, after which we detect the changes in the phenotypical, physiological, hormone content, and performed a transcriptome analysis to explain SA influence alfalfa in freezing stress. The results demonstrated that exogenous SA could improve the accumulation of free SA in alfalfa leaves primarily through the phenylalanine ammonia-lyase pathway. Moreover, the results of transcriptome analysis revealed that the mitogen-activated protein kinase (MAPK) signaling pathway-plant play a critical role in SA alleviating freezing stress. In addition, the weighted gene co-expression network analysis (WGCNA) found that MPK3, MPK9, WRKY22 (downstream target gene of MPK3), and TGACG-binding factor 1 (TGA1) are candidate hub genes involved in freezing stress defense, all of which are involved in the SA signaling pathway. Therefore, we conclude that SA could possibly induce MPK3 to regulate WRKY22 to participate in freezing stress to induced gene expression related to SA signaling pathway (NPR1-dependent pathway and NPR1-independent pathway), including the genes of non-expresser of pathogenesis-related gene 1 (NPR1), TGA1, pathogenesis-related 1 (PR1), superoxide dismutase (SOD), peroxidase (POD), ascorbate peroxidase (APX), glutathione-S-transferase (GST), and heat shock protein (HSP). This enhanced the production of antioxidant enzymes such as SOD, POD, and APX, which increases the freezing stress tolerance of alfalfa plants.

Magnesium deficiency stress in rice can be alleviated by partial nitrate nutrition supply

The problem of nitrogen (N) excess and magnesium (Mg) deficiency in farmland is becoming more common, severe, and widespread in southern China. Magnesium is known to be an essential nutrient for higher plants; however, the physiological responses of field crops to Mg deficiency, particularly to its interaction with N forms, remain largely unknown. In this study, a hydroponic experiment was conducted using three Mg levels (0.01, 1.00, and 5.00 mM) and three nitrate/ammonium ratios (NO₃^-/NH₄⁺ of 0/100, 25/75, and 50/50) under greenhouse conditions. The results show that Mg deficiency (0.01 mM) could result in yellow leaves, dwarf plants, and fewer tillers during rice growth. Furthermore, Mg deficiency induced a major reduction in root morphology and activity, photosynthetic properties, and nutrient accumulation, while it resulted in a clear increase in malondialdehyde, superoxide dismutase, peroxidase, and catalase activities in rice. However, under Mg-deficiency stress, the supply of partial NO₃^- led to a significant drop in these antioxidant enzyme activities. Moreover, partial NO₃^- supply significantly improved the net photosynthetic rate, transpiration rate, stomatal conductance, and intercellular CO₂ concentrations under Mg-deficiency conditions. In particular, the supply of partial NO₃^- dramatically promoted the growth of the root system, boosted the occurrence of lateral roots, and enhanced root vitality under Mg-deficiency stress. Additionally, the supply of partial NO₃^- led to significant increases in dry weight and N and Mg contents under Mg deficiency. The results of this study suggest that the symptoms of Mg-deficiency stress in rice can be alleviated by partial NO₃^- supply.

Emerging Roles of Salicylic Acid in Plant Saline Stress Tolerance

One of the most important phytohormones is salicylic acid (SA), which is essential for the regulation of plant growth, development, ripening, and defense responses. The role of SA in plant-pathogen interactions has attracted a lot of attention. Aside from defense responses, SA is also important in responding to abiotic stimuli. It has been proposed to have great potential for improving the stress resistance of major agricultural crops. On the other hand, SA utilization is dependent on the dosage of the applied SA, the technique of application, and the status of the plants (e.g., developmental stage and acclimation). Here, we reviewed the impact of SA on saline stress responses and the associated molecular pathways, as well as recent studies toward understanding the hubs and crosstalk between SA-induced tolerances to biotic and saline stress. We propose that elucidating the mechanism of the SA-specific response to various stresses, as well as SA-induced rhizosphere-specific microbiome modeling, may provide more insights and support in coping with plant saline stress.

LIP5, a MVB biogenesis regulator, is required for rice growth

LYST-INTERACTING PROTEIN5 (LIP5) is a conserved regulator of multivesicular body (MVB) biogenesis in eukaryotes. In Arabidopsis, AtLIP5 is a target of stress-responsive MITOGEN-ACTIVATED PROTEIN KINASE3 and 6 and mediates stress-induced MVB biogenesis to promote stress responses. However, Arabidopsis atlip5 knockout mutants are normal in growth and development. Here we report that rice OsLIP5 gene could fully restore both the disease resistance and salt tolerance of the Arabidopsis oslip5 mutant plants to the wild-type levels. Unlike Arabidopsis atlip5 mutants, rice oslip5 mutants were severely stunted, developed necrotic lesions and all died before flowering. Unlike in Arabidopsis, LIP5 regulated endocytosis under both stress and normal conditions in rice. These findings indicate that there is strong evolutionary divergence among different plants in the role of the conserved LIP5-regulated MVB pathway in normal plant growth.

The origin and evolution of salicylic acid signaling and biosynthesis in plants

Salicylic acid (SA) plays a pivotal role in plant response to biotic and abiotic stress. Several core SA signaling regulators and key proteins in SA biosynthesis have been well characterized. However, much remains unknown about the origin, evolution, and early diversification of core elements in plant SA signaling and biosynthesis. In this study, we identified 10 core protein families in SA signaling and biosynthesis across green plant lineages. We found that the key SA signaling receptors, the nonexpresser of pathogenesis-related (NPR) proteins, originated in the most recent common ancestor (MRCA) of land plants and formed divergent groups in the ancestor of seed plants. However, key transcription factors for SA signaling, TGACG motif-binding proteins (TGAs), originated in the MRCA of streptophytes, arguing for the stepwise evolution of core SA signaling in plants. Different from the assembly of the core SA signaling pathway in the ancestor of seed plants, SA exists extensively in green plants, including chlorophytes and streptophyte algae. However, the full isochorismate synthase (ICS)-based SA synthesis pathway was first assembled in the MRCA of land plants. We further revealed that the ancient abnormal inflorescence meristem 1 (AIM1)-based β-oxidation pathway is crucial for the biosynthesis of SA in chlorophyte algae, and this biosynthesis pathway may have facilitated the adaptation of early-diverging green algae to the high-light-intensity environment on land. Taken together, our findings provide significant insights into the early evolution and diversification of plant SA signaling and biosynthesis pathways, highlighting a crucial role of SA in stress tolerance during plant terrestrialization.

Multi-model genome-wide association studies of leaf anatomical traits and vein architecture in rice

Introduction

The anatomy of rice leaves is closely related to photosynthesis and grain yield. Therefore, exploring insight into the quantitative trait loci (QTLs) and alleles related to rice flag leaf anatomical and vein traits is vital for rice improvement.

Methods

Here, we aimed to explore the genetic architecture of eight flag leaf traits using one single-locus model; mixed-linear model (MLM), and two multi-locus models; fixed and random model circulating probability unification (FarmCPU) and Bayesian information and linkage disequilibrium iteratively nested keyway (BLINK). We performed multi-model GWAS using 329 rice accessions of RDP1 with 700K single-nucleotide polymorphisms (SNPs) markers.

Results

The phenotypic correlation results indicated that rice flag leaf thickness was strongly correlated with leaf mesophyll cells layer (ML) and thickness of both major and minor veins. All three models were able to identify several significant loci associated with the traits. MLM identified three non-synonymous SNPs near NARROW LEAF 1 (NAL1) in association with ML and the distance between minor veins (IVD) traits.

Discussion

Several numbers of significant SNPs associated with known gene function in leaf development and yield traits were detected by multi-model GWAS performed in this study. Our findings indicate that flag leaf traits could be improved via molecular breeding and can be one of the targets in high-yield rice development.

Dynamic and fluctuating generation of hydrogen peroxide via photorespiratory metabolic channeling in plants

The homeostasis of hydrogen peroxide (H₂ O₂ ), a key regulator of basic biological processes, is a result of the cooperation between its generation and scavenging. However, the mechanistic basis of this balance is not fully understood. We previously proposed that the interaction between glycolate oxidase (GLO) and catalase (CAT) may serve as a molecular switch that modulates H₂ O₂ levels in plants. In this study, we demonstrate that the GLO-CAT complex in plants exists in different states, which are dynamically interchangeable in response to various stimuli, typically salicylic acid (SA), at the whole-plant level. More crucially, changes in the state of the complex were found to be closely linked to peroxisomal H₂ O₂ fluctuations, which were independent of the membrane-associated NADPH oxidase. Furthermore, evidence suggested that H₂ O₂ channeling occurred even in vitro when GLO and CAT worked cooperatively. These results demonstrate that dynamic changes in H₂ O₂ levels are physically created via photorespiratory metabolic channeling in plants, and that such H₂ O₂ fluctuations may serve as signals that are mechanistically involved in the known functions of photorespiratory H₂ O₂ . In addition, our study also revealed a new way for SA to communicate with H₂ O₂ in plants.

The interaction of ABA and ROS in plant growth and stress resistances

The plant hormone ABA (abscisic acid) plays an extremely important role in plant growth and adaptive stress, including but are not limited to seed germination, stomatal closure, pathogen infection, drought and cold stresses. Reactive oxygen species (ROS) are response molecules widely produced by plant cells under biotic and abiotic stress conditions. The production of apoplast ROS is induced and regulated by ABA, and participates in the ABA signaling pathway and its regulated plant immune system. In this review, we summarize ABA and ROS in apoplast ROS production, plant response to biotic and abiotic stresses, plant growth regulation, ABA signal transduction, and the regulatory relationship between ABA and other plant hormones. In addition, we also discuss the effects of protein post-translational modifications on ABA and ROS related factors.

Global transcriptome and coexpression network analyses reveal cultivar-specific molecular signatures associated with different rooting depth responses to drought stress in potato

Potato is one of the most important vegetable crops worldwide. Its growth, development and ultimately yield is hindered by drought stress condition. Breeding and selection of deep-rooted and drought-tolerant potato varieties has become a prime approach for improving the yield and quality of potato (Solanum tuberosum L.) in arid and semiarid areas. A comprehensive understanding of root development-related genes has enabled scientists to formulate strategies to incorporate them into breeding to improve complex agronomic traits and provide opportunities for the development of stress tolerant germplasm. Root response to drought stress is an intricate process regulated through complex transcriptional regulatory network. To understand the rooting depth and molecular mechanism, regulating root response to drought stress in potato, transcriptome dynamics of roots at different stages of drought stress were analyzed in deep (C119) and shallow-rooted (C16) cultivars. Stage-specific expression was observed for a significant proportion of genes in each cultivar and it was inferred that as compared to C16 (shallow-rooted), approximately half of the genes were differentially expressed in deep-rooted cultivar (C119). In C16 and C119, 11 and 14 coexpressed gene modules, respectively, were significantly associated with physiological traits under drought stress. In a comparative analysis, some modules were different between the two cultivars and were associated with differential response to specific drought stress stage. Transcriptional regulatory networks were constructed, and key components determining rooting depth were identified. Through the results, we found that rooting depth (shallow vs deep) was largely determined by plant-type, cell wall organization or biogenesis, hemicellulose metabolic process, and polysaccharide metabolic process. In addition, candidate genes responding to drought stress were identified in deep (C119) and shallow (C16) rooted potato varieties. The results of this study will be a valuable source for further investigations on the role of candidate gene(s) that affect rooting depth and drought tolerance mechanisms in potato.

Salicylic Acid Acts Upstream of Auxin and Nitric Oxide (NO) in Cell Wall Phosphorus Remobilization in Phosphorus Deficient Rice

Salicylic acid (SA) is thought to be involved in phosphorus (P) stress response in plants, but the underlying molecular mechanisms are poorly understood. Here, we showed that P deficiency significantly increased the endogenous SA content by inducing the SA synthesis pathway, especially for up-regulating the expression of PAL3. Furthermore, rice SA synthetic mutants pal3 exhibited the decreased root and shoot soluble P content, indicating that SA is involved in P homeostasis in plants. Subsequently, application of exogenous SA could increase the root and shoot soluble P content through regulating the root and shoot cell wall P reutilization. In addition, - P + SA treatment highly upregulated the expression of P transporters such as OsPT2 and OsPT6, together with the increased xylem P content, suggesting that SA also participates in the translocation of the P from the root to the shoot. Moreover, both signal molecular nitric oxide (NO) and auxin (IAA) production were enhanced when SA is applied while the addition of respective inhibitor c-PTIO (NO scavenger) and NPA (IAA transport inhibitor) significantly decreased the root and shoot cell wall P remobilization in response to P starvation. Taken together, here SA-IAA-NO-cell wall P reutilization pathway has been discovered in P-starved rice.

ROS-stimulated Protein Lysine Acetylation Is Required for Crown Root Development in Rice

INTRODUCTION

As signal molecules in aerobic organisms, locally accumulated ROS have been reported to balance cell division and differentiation in the root meristem. Protein posttranslational modifications such as lysine acetylation play critical roles in controlling a variety of cellular processes. However, the mechanism by which ROS regulate root development is unknown. In addition, how protein lysine acetylation is regulated and whether cellular ROS levels affect protein lysine acetylation remain unclear.

OBJECTIVES

We aimed to elucidate the relationship between ROS and protein acetylation by exploring a rice mutant plant that displays a decreased level of ROS in postembryonic crown root (CR) cells and severe defects in CR development.

METHODS

First, proteomic analysis was used to find candidate proteins responsible for the decrease of ROS detected in the wox11 mutant. Then, biochemical, molecular, and genetic analyses were used to study WOX11-regulated genes involved in ROS homeostasis. Finally, acetylproteomic analysis of wild type and wox11 roots treated with or without potassium iodide (KI) and peroxide (H₂O₂) were used to study the effects of ROS on protein acetylation in rice CR cells.

RESULTS

We demonstrated that WOX11 was required to maintain ROS homeostasis by upregulating peroxidase genes in the crown root meristem. Acetylproteomic analysis revealed that WOX11-dependent peroxide (H₂O₂) levels in CR cells promoted lysine acetylation of many non-histone proteins enriched for nitrogen metabolism and peptide/protein synthesis pathways. Further analysis revealed that the redox state affected histone deacetylases (HDACs) activity, which was likely related to the high levels of protein lysine acetylation in CR cells.

CONCLUSION

WOX11-controlled ROS level in CR meristem cells is required for protein lysine acetylation which represents a mechanism of ROS-promoted CR development in rice.

Hypersensitivity-Related Genes HSR201 and HSR203J Are Regulated by Calmodulin-Binding Protein 60-Type Transcription Factors and Required for Pathogen Signal-Induced Salicylic Acid Synthesis

Salicylic acid (SA) plays a key role in plant resistance to pathogens. In Arabidopsis, the isochorismate synthase pathway mainly contributes to pathogen-induced SA synthesis, and the expression of SA synthesis genes is activated by two calmodulin (CaM)-binding protein 60 (CBP60)-type transcription factors, CBP60g and SARD1. In tobacco, the mechanisms underlying SA synthesis remain largely unknown. SA production is induced by wounding in tobacco plants in which the expression of two stress-related mitogen-activated protein kinases is suppressed. Using this phenomenon, we identified genes whose expression is associated with SA synthesis. One of the genes, NtCBP60g, showed 23% amino acid sequence identity with CBP60g. Transient overexpression of NtCBP60g as well as NtSARD1, a tobacco homolog of SARD1, induced SA accumulation in Nicotiana benthamiana leaves. NtCBP60g and NtSARD1 bound CaM, and CaM enhanced SA accumulation induced by NtCBP60g and NtSARD1. Conversely, mutations in NtCBP60g and NtSARD1 that abolished CaM binding reduced their ability to induce SA. Expression profiling and promoter analysis identified two hypersensitivity-related genes, HSR201 and HSR203J as the targets of NtCBP60g and NtSARD1. Virus-induced gene silencing of both NtCBP60g and NtSARD1 homologs compromised SA accumulation and the expression of HSR201 and HSR203J homologs, which were induced by a pathogen-derived elicitor in N. benthamiana leaves. Moreover, elicitor-induced SA accumulation was compromised by silencing of the HSR201 homolog and the HSR203J homolog. These results suggested that HSR201 and HSR203J are regulated by NtCBP60g and NtSARD1 and are required for elicitor-induced SA synthesis.

CeO2 Nanoparticles Seed Priming Increases Salicylic Acid Level and ROS Scavenging Ability to Improve Rapeseed Salt Tolerance

Soil salinity is a major issue limiting efficient crop production. Seed priming with nanomaterials (nanopriming) is a cost-effective technology to improve seed germination under salinity; however, the underlying mechanisms still need to be explored. Here, polyacrylic acid coated nanoceria (cerium oxide nanoparticles) (PNC, 9.2 nm, -38.7 mV) are synthesized and characterized. The results show that under salinity, PNC priming significantly increases rapeseed shoot length (41.5%), root length (93%), and seedling dry weight (78%) compared to the no-nanoparticle (NNP) priming group. Confocal imaging results show that compared with NNP group, PNC priming significantly reduces reactive oxygen species (ROS) level in leaf (94.3% of H2O2, 56.4% of •O2 -) and root (38.4% of H2O2, 41.3% of •O2 -) of salt stressed rapeseed seedlings. Further, the results show that compared with the NNP group, PNC priming not only increases salicylic acid (SA) content in shoot (51.3%) and root (78.4%), but also upregulates the expression of SA biosynthesis related genes in salt stressed rapeseed. Overall, PNC nanopriming improved rapeseed salt tolerance is associated with both the increase of ROS scavenging ability and the increase of salicylic acid. The results add more information to understand the complexity of mechanisms behind nanoceria priming improved plant salt tolerance.

Generation of the salicylic acid deficient Arabidopsis via a synthetic salicylic acid hydroxylase expression cassette

BACKGROUND

Salicylic acid (SA) is one of the plant hormones, which plays crucial roles in signaling transduction in plant growth, disease resistance, and leaf senescence. Arabidopsis (Arabidopsis thaliana) SA 3-hydroxylase (S3H) and 5-hydroxylase (S5H) are key enzymes which maintain SA homeostasis by catalyzing SA to 2,3-dihydroxybenzoic acid (DHBA) and 2,5-DHBA, respectively.

RESULTS

SA deficient transgenic Arabidopsis lines were generated by introducing two binary vectors S5Hpro::EGFP-S3H and 35Spro::EGFP-S3H respectively, in which the expression of S3H is under the control of the S5H promoter or CaMV 35S promoter. Compared with the constitutive expression of S3H gene under the control of 35S promoter, the S3H gene under the native S5H promoter is activated by endogenous SA and results in a dynamic control of SA catabolism in a feedback mode. The SA accumulation, growth, leaf senescence, and pathogen resistance of the S5Hpro::GFP-S3H transgenic plants were investigated in parallel with NahG transgenic plants. The SA levels in the S5Hpro::EGFP-S3H transgenic plants were similar to or slightly lower than those of NahG transgenic Arabidopsis and resulted in SA deficient phenotypes. The low-SA trait of the S5Hpro::EGFP-S3H transgenic lines was inherited stably in the later generations.

CONCLUSIONS

Compared with NahG transgenic lines producing by-product catechol, S5Hpro::EGFP-S3H transgenic lines reduce SA levels by converting SA to a native product 2,3-DHBA for catabolism. Together, we provide new SA-deficient germplasms for the investigations of SA signaling in plant development, leaf senescence, and disease resistance.

From Soil Amendments to Controlling Autophagy: Supporting Plant Metabolism under Conditions of Water Shortage and Salinity

Crop resistance to environmental stress is a major issue. The globally increasing land degradation and desertification enhance the demand on management practices to balance both food and environmental objectives, including strategies that tighten nutrient cycles and maintain yields. Agriculture needs to provide, among other things, future additional ecosystem services, such as water quantity and quality, runoff control, soil fertility maintenance, carbon storage, climate regulation, and biodiversity. Numerous research projects have focused on the food–soil–climate nexus, and results were summarized in several reviews during the last decades. Based on this impressive piece of information, we have selected only a few aspects with the intention of studying plant–soil interactions and methods for optimization. In the short term, the use of soil amendments is currently attracting great interest to cover the current demand in agriculture. We will discuss the impact of biochar at water shortage, and plant growth promoting bacteria (PGPB) at improving nutrient supply to plants. In this review, our focus is on the interplay of both soil amendments on primary reactions of photosynthesis, plant growth conditions, and signaling during adaptation to environmental stress. Moreover, we aim at providing a general overview of how dehydration and salinity affect signaling in cells. With the use of the example of abscisic acid (ABA) and ethylene, we discuss the effects that can be observed when biochar and PGPB are used in the presence of stress. The stress response of plants is a multifactorial trait. Nevertheless, we will show that plants follow a general concept to adapt to unfavorable environmental conditions in the short and long term. However, plant species differ in the upper and lower regulatory limits of gene expression. Therefore, the presented data may help in the identification of traits for future breeding of stress-resistant crops. One target for breeding could be the removal and efficient recycling of damaged as well as needless compounds and structures. Furthermore, in this context, we will show that autophagy can be a useful goal of breeding measures, since the recycling of building blocks helps the cells to overcome a period of imbalanced substrate supply during stress adjustment.

Physiological mechanisms of ABA-induced salinity tolerance in leaves and roots of rice

Abscisic acid (ABA) plays a crucial role in response to abiotic stress as important small molecules in regulating metabolism. This study aimed to evaluate the ability of foliar spraying ABA to regulate growth quality at rice seedling stage under salt stress. Results demonstrated that salt stress strongly reduced all the growth parameters of two rice seedlings ('Chaoyouqianhao' and 'Huanghuazhan'), caused prominent decrease in the levels of photosynthetic pigments (mainly in Huanghuazhan), photosynthesis and fluorescence parameters. Salinity treatment increased the concentration of malondialdehyde (MDA) and hydrogen peroxide (H2O2) in roots, whereas significant decreased H2O2 was found in leaves of Huanghuazhan. Additionally, salinity triggered high Na+ content particularly in leaves and enhanced catalase (CAT) activities, ascorbate peroxidase (APX) and peroxidase (POD) activities of the two rice seedlings. Nevertheless, salinity-induced increased root ascorbic acid (AsA) and glutathione (GSH) levels while decreased in leaves, which depended on treatment time. Conversely, ABA application partially or completely mitigated salinity toxicity on the seedlings. ABA could reverse most of the changed physiological parameters triggered by salt stress. Specially, ABA treatment improved antioxidant enzyme levels and significantly reduced the Na+ content of two varieties as well as increased the K+, Mg2+ and Ca2+ content in leaves and roots. ABA treatment increased the hormone contents of 1-aminocclopropane carboxylic acid (ACC), trans-zeatin (TZ), N6-isopentyladenosine (IPA), Indole-3-acetic acid (IAA), and ABA in leaves of two rice varieties under salt stress. It is suggested that ABA was beneficial to protect membrane lipid peroxidation, the modulation of antioxidant defense systems and endogenous hormonal balance with imposition to salt stress.