Transcriptional Coactivators: Driving Force of Plant Immunity

Enhanced Disease Susceptibility1 Regulates Immune Response in Lotus japonicus

Enhanced disease susceptibility1 (EDS1) is a key node in the plant immune signaling network, regulating salicylic acid (SA) levels and other immune responses in Arabidopsis thaliana. We previously reported that modulation of SA by AGD2-like defense response protein 1 (ALD1) has been shown to influence the immune response in Lotus japonicus, but the role of LjEDS1 in this species remains unclear. Here, we identified and characterized the LjEDS1 gene in L. japonicus. The LjEDS1 protein contains a lipase-like domain and an EP domain similar to the Arabidopsis EDS1 protein. Subcellular localization studies revealed that the LjEDS1 protein is distributed in both the cytoplasm and nucleus. Heterologous expression of LjEDS1 in the Arabidopsis ateds1 mutant increased resistance to Pseudomonas syringae pv. Tomato (Pst) strain DC3000. In L. japonicus, roots of the ljeds1 mutants exhibited heightened susceptibility to Ralstonia solanacearum, with increased lesion areas and bacterial titers. Conversely, the overexpression of LjEDS1 reduced the lesion areas and bacterial titers in roots infected with R. solanacearum compared to those in the wild-type. Gene expression analysis showed that LjEDS1 regulates defense-related, basal immunity, and oxidative stress response genes in L. japonicus roots. These findings establish LjEDS1 as an important regulator of disease resistance in L. japonicus.

Identification of plant resistance inducers and evaluation of genotype receptivity for carrot protection against Alternaria leaf blight

The use of biopesticides represents an alternative strategy to synthetic chemical products for crop protection. To promote their adoption and effective use by growers, it is crucial to understand their modes of action and the optimal conditions for their application in crops, including their compatibility with specific varieties. Through a series of greenhouse experiments, this study describes the development and validation of a robust molecular diagnostic tool for enabling the evaluation of defence gene activation. The results identified plant resistance inducers (PRIs) among biopesticide products capable of protecting carrots against Alternaria leaf blight. By applying a PRI to a range of carrot varieties exhibiting varying levels of resistance to Alternaria dauci, preliminary findings on plant receptivity suggest that the efficacy of PRIs in conferring protection is highly dependent on the treated variety. Two distinct genotype-dependent effects were observed: sensitivity to the PRI and an enhancement of resistance. This study offers new insights into optimising biopesticide use in carrot cultivation.

Interaction between pathogenesis-related (PR) proteins and phytohormone signaling pathways in conferring disease tolerance in plants

Pathogenesis-related (PR) proteins are critical defense signaling molecules induced by phytopathogens. They play a vital role in plant's defense signaling pathways and innate immunity, particularly in systemic acquired resistance (SAR) and serve as key molecular markers of plant defense. Overexpressing PR genes, such as chitinase, thaumatin, glucanase, thionin and defensin, either individually or in combination, have significantly boosted plants' defense responses against various pathogens. However, signaling pathways regulating the expression of these versatile proteins remain only partially understood. Plant hormones like salicylic acid (SA) and jasmonic acid (JA) are known for their well-established roles in regulating PR gene responses to pathogens and other stress conditions. PR genes interact with various components of hormonal signaling pathways, including receptors (e.g., NPR1 in SA signaling), transcription factors (e.g., MYC2 in JA signaling), and cis-regulating elements (e.g., W-box), to modulate plant defense responses. Recent studies have highlighted the contributions of different plant hormones to plant immunity and their interactions with PR proteins in a process known as hormonal crosstalk, which helps coordinate immunity activation. This review provides a comprehensive overview of the PR proteins, their complexity, and hormonal crosstalk in immunity, aiming to understand these interactions for improved pathogen resistance.

The transcriptional response to yellow and wilt disease, caused by race 6 of Fusarium oxysporum f. sp. Ciceris in two contrasting chickpea cultivars

BACKGROUND

Chickpea (Cicer arietinum L.) ranks as the third most crucial grain legume worldwide. Fusarium wilt (Fusarium oxysporum f. sp. ciceri (Foc)) is a devastating fungal disease that prevents the maximum potential for chickpea production.

RESULTS

To identify genes and pathways involved in resistance to race 6 of Foc, this study utilized transcriptome sequencing of two chickpea cultivars: resistant (Ana) and susceptible (Hashem) to Foc race 6. Illumina sequencing of the root samples yielded 133.5 million raw reads, with about 90% of the clean reads mapped to the chickpea reference genome. The analysis revealed that 548 genes (332 upregulated and 216 downregulated) in the resistant genotype (Ana) and 1115 genes (595 upregulated and 520 downregulated) in the susceptible genotype (Hashem) were differentially expressed under Fusarium wilt (FW) disease stress caused by Foc race 6. The expression patterns of some differentially expressed genes (DEGs) were validated using quantitative real-time PCR. A total of 131 genes were exclusively upregulated under FW stress in the resistant cultivar, including several genes involved in sensing (e.g., CaNLR-RPM1, CaLYK5-RLK, CaPR5-RLK, CaLRR-RLK, and CaRLP-EIX2), signaling (e.g., CaPP7, CaEPS1, CaSTY13, and CaPR-1), transcription regulation (e.g., CaMYBs, CaGLK, CaERFs, CaZAT11-like, and CaNAC6) and cell wall integrity (e.g., CaPGI2-like, CaEXLs, CaCSLD and CaCYP73A100-like).

CONCLUSIONS

The achieved results could provide insights into the molecular mechanism underlying resistance to FW and could be valuable for breeding programs aimed at developing FW-resistant chickpea varieties.

Cullin-Conciliated Regulation of Plant Immune Responses: Implications for Sustainable Crop Protection

Cullins are crucial components of the ubiquitin-proteasome system, playing pivotal roles in the regulation of protein metabolism. This review provides insight into the wide-ranging functions of cullins, particularly focusing on their impact on plant growth, development, and environmental stress responses. By modulating cullin-mediated protein mechanisms, researchers can fine-tune hormone-signaling networks to improve various agronomic traits, including plant architecture, flowering time, fruit development, and nutrient uptake. Furthermore, the targeted manipulation of cullins that are involved in hormone-signaling pathways, e.g., cytokinin, auxin, gibberellin, abscisic acids, and ethylene, can boost crop growth and development while increasing yield and enhancing stress tolerance. Furthermore, cullins also play important roles in plant defense mechanisms through regulating the defense-associated protein metabolism, thus boosting resistance to pathogens and pests. Additionally, this review highlights the potential of integrating cullin-based strategies with advanced biological tools, such as CRISPR/Cas9-mediated genome editing, genetic engineering, marker-associated selections, gene overexpression, and gene knockout, to achieve precise modifications for crop improvement and sustainable agriculture, with the promise of creating resilient, high-yielding, and environmentally friendly crop varieties.

Advances in functional studies of plant MYC transcription factors

Myelocytomatosis (MYC) transcription factors (TFs) belong to the basic helix-loop-helix (bHLH) family in plants and play a central role in governing a wide range of physiological processes. These processes encompass plant growth, development, adaptation to biotic and abiotic stresses, as well as secondary metabolism. In recent decades, significant strides have been made in comprehending the multifaceted regulatory functions of MYCs. This advancement has been achieved through the cloning of MYCs and the characterization of plants with MYC deficiencies or overexpression, employing comprehensive genome-wide 'omics' and protein-protein interaction technologies. MYCs act as pivotal components in integrating signals from various phytohormones' transcriptional regulators to orchestrate genome-wide transcriptional reprogramming. In this review, we have compiled current research on the role of MYCs as molecular switches that modulate signal transduction pathways mediated by phytohormones and phytochromes. This comprehensive overview allows us to address lingering questions regarding the interplay of signals in response to environmental cues and developmental shift. It also sheds light on the potential implications for enhancing plant resistance to diverse biotic and abiotic stresses through genetic improvements achieved by plant breeding and synthetic biology efforts.

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.

Integration of metabolomics and transcriptomics reveals the regulation mechanism of the phenylpropanoid biosynthesis pathway in insect resistance traits in Solanum habrochaites

Solanum habrochaites (SH), a wild species closely related to 'Ailsa Craig' (AC), is an important germplasm resource for modern tomato breeding. Trichomes, developed from epidermal cells, have a role in defense against insect attack, and their secretions are of non-negligible value. Here, we found that the glandular heads of type VI trichomes were clearly distinguishable between AC and SH under cryo-scanning electron microscopy, the difference indicating that SH could secrete more anti-insect metabolites than AC. Pest preference experiments showed that aphids and mites preferred to feed near AC compared with SH. Integration analysis of transcriptomics and metabolomics data revealed that the phenylpropanoid biosynthesis pathway was an important secondary metabolic pathway in plants, and SH secreted larger amounts of phenylpropanoids and flavonoids than AC by upregulating the expression of relevant genes in this pathway, and this may contribute to the greater resistance of SH to phytophagous insects. Notably, virus-induced silencing of Sl4CLL6 not only decreased the expression of genes downstream of the phenylpropanoid biosynthesis pathway (SlHCT, SlCAD, and SlCHI), but also reduced resistance to mites in tomato. These findings provided new genetic resources for the synthesis of phenylpropanoid compounds and anti-insect breeding in S. habrochaites and a new theoretical basis for the improvement of important traits in cultivated tomato.

Non-specific LIPID TRANSFER PROTEIN 1 enhances immunity against tobacco mosaic virus in Nicotiana benthamiana

Plant non-specific lipid transfer proteins (nsLTPs) are small, cysteine-rich proteins that play significant roles in biotic and abiotic stress responses; however, the molecular mechanism of their functions against viral infections remains unclear. In this study, we employed virus-induced gene-silencing and transgenic overexpression to functionally analyse a type-I nsLTP in Nicotiana benthamiana, NbLTP1, in the immunity response against tobacco mosaic virus (TMV). NbLTP1 was inducible by TMV infection, and its silencing increased TMV-induced oxidative damage and the production of reactive oxygen species (ROS), compromised local and systemic resistance to TMV, and inactivated the biosynthesis of salicylic acid (SA) and its downstream signaling pathway. The effects of NbLTP1-silencing were partially restored by application of exogenous SA. Overexpressing NbLTP1 activated genes related to ROS scavenging to increase cell membrane stability and maintain redox homeostasis, confirming that an early ROS burst followed by ROS suppression at the later phases of pathogenesis is essential for resistance to TMV infection. The cell-wall localization of NbLTP1 was beneficial to viral resistance. Overall, our results showed that NbLTP1 positively regulates plant immunity against viral infection through up-regulating SA biosynthesis and its downstream signaling component, NONEXPRESSOR OF PATHOGENESIS-RELATED 1 (NPR1), which in turn activates pathogenesis-related genes, and by suppressing ROS accumulation at the later phases of viral pathogenesis.

Genetic and morphological variants of Acidovorax avenae subsp. avenae cause red stripe of sugarcane in China

Sugarcane (Saccharum spp.) is an important cash crop for production of sugar and bioethanol. Red stripe caused by Acidovorax avenae subsp. avenae (Aaa) is a disease that occurs in numerous sugarcane-growing regions worldwide. In this study, 17 strains of Aaa were isolated from 13 symptomatic leaf samples in China. Nine of these strains produced white-cream colonies on nutrient agar medium while the other eight produced yellow colonies. In pairwise sequence comparisons of the 16S-23S rRNA internally transcribed spacer (ITS), the 17 strains had 98.4-100% nucleotide identity among each other and 98.2-99.5% identity with the reference strain of Aaa (ATCC 19860). Three RFLP patterns based on this ITS sequence were also found among the strains of Aaa obtained in this study. Multilocus sequence typing (MLST) based on five housekeeping genes (ugpB, pilT, lepA, trpB, and gltA) revealed that the strains of Aaa from sugarcane in China and a strain of Aaa (30179) isolated from sorghum in Brazil formed a unique evolutionary subclade. Twenty-four additional strains of Aaa from sugarcane in Argentina and from other crops worldwide were distributed in two other and separate subclades, suggesting that strains of A. avenae from sugarcane are clonal populations with local specificities. Two strains of Aaa from China (CNGX08 forming white-cream colored colonies and CNGD05 forming yellow colonies) induced severe symptoms of red stripe in sugarcane varieties LC07-150 and ZZ8 but differed based on disease incidence in two separate inoculation experiments. Infected plants also exhibited increased salicylic acid (SA) content and transcript expression of gene PR-1, indicating that the SA-mediated signal pathway is involved in the response to infection by Aaa. Consequently, red stripe of sugarcane in China is caused by genetically different strains of Aaa and at least two morphological variants. The impact of these independent variations on epidemics of red stripe remains to be investigated.

In vivo Imaging Enables Understanding of Seamless Plant Defense Responses to Wounding and Pathogen Attack

Plants are exposed to varied biotic stresses, including sequential or simultaneous attack by insects and pathogens. To overcome these complex stresses, plants must perceive each of the stresses, then integrate and relay the information throughout the plant body and eventually activate local and systemic resistance responses. Previous molecular genetic studies identified jasmonic acid and salicylic acid as key plant hormones of wound and immune responses. These hormones, combined with their antagonistic interaction, play critical roles in the initiation and regulation of defense responses against insects and pathogens. Aside from molecular and genetic information, the latest in vivo imaging technology has revealed that plant defense responses are regulated spatially and temporally. In this review, we summarize the current knowledge of local and systemic defense responses against wounding and diseases with a focus on past and recent advances in imaging technologies. We discuss how imaging-based multiparametric analysis has improved our understanding of the spatiotemporal regulation of dynamic plant stress responses. We also emphasize the importance of compiling the knowledge generated from individual studies on plant wounding and immune responses for a more seamless understanding of plant defense responses in the natural environment.

Genome-Wide Characterization and Identification of the YABBY Gene Family in Mango (Mangifera indica)

YABBY is a specific transcription factor gene family in plants. It has the typical N-terminal C2C2-type zinc-finger domain and the C-terminal YABBY conservative structure domain, which play an important role in the development of the leaves and floral organs. The YABBY gene family directs leaf polarity in mango, playing an important role in maintaining species specificity. In this study, a total of seven YABBY genes were identified in the mango (Mangifera indica) genome. The seven YABBY family members possessed both typical C2C2 and YABBY domains. A phylogenetic tree was constructed based on the amino acid sequences of the 42 YABBY proteins of mango, Arabidopsis, apple, grape, and peach. The phylogenetic tree indicated that the members of the mango YABBY family could be divided into three subfamilies, including CRC, YAB5, and YAB3. Quantitative real-time PCR showed that the transcription levels of the MiYABBYs were significantly different under biotic and abiotic stresses. The transcription level of MiYABBY7 was significantly down-regulated at 0–72 h after Xanthomonas campestris pv. mangiferaeindicae infection, methyl jasmonate and salicylic acid stresses. The MiYABBY1 transcription level was significantly down-regulated at 0–72 h after Colletotrichum gloeosporioides infection. MiYABBYs were expressed specifically in different leaves and fruit, and MiYABBY6 was significantly up-regulated during leaf and fruit development. However, MiYABBY5 showed a contrary transcriptional pattern during leaf and fruit development. This is first report on the mango YABBY gene family at the genome-wide level. These results will be beneficial for understanding the biological functions and molecular mechanisms of YABBY genes.

A vigilant gliding bird protects plants

The plant hormone salicylic acid (SA) receptor NONEXPRESSOR OF PATHOGENESIS-RELATED PROTEINS1 (NPR1) plays a critical role for plant defense against biotrophic and hemi-biotrophic pathogens. In a milestone paper, Kumar, Zavaliev, Wu et al. unraveled the structural basis for the assembly of an enhanceosome by NPR1 in activating the expression of plant defense genes.

The Interplay between Hydrogen Sulfide and Phytohormone Signaling Pathways under Challenging Environments

Hydrogen sulfide (H₂S) serves as an important gaseous signaling molecule that is involved in intra- and intercellular signal transduction in plant–environment interactions. In plants, H₂S is formed in sulfate/cysteine reduction pathways. The activation of endogenous H₂S and its exogenous application has been found to be highly effective in ameliorating a wide variety of stress conditions in plants. The H₂S interferes with the cellular redox regulatory network and prevents the degradation of proteins from oxidative stress via post-translational modifications (PTMs). H₂S-mediated persulfidation allows the rapid response of proteins in signaling networks to environmental stimuli. In addition, regulatory crosstalk of H₂S with other gaseous signals and plant growth regulators enable the activation of multiple signaling cascades that drive cellular adaptation. In this review, we summarize and discuss the current understanding of the molecular mechanisms of H₂S-induced cellular adjustments and the interactions between H₂S and various signaling pathways in plants, emphasizing the recent progress in our understanding of the effects of H₂S on the PTMs of proteins. We also discuss future directions that would advance our understanding of H₂S interactions to ultimately mitigate the impacts of environmental stresses in the plants.