Molecular plant pathology最新文献

Pseudomonas syringae pv. tabaci (Pta) is an important plant pathogen, which causes wildfire disease in Nicotiana species. However, the genetic basis underlying strain-level differences in virulence remains largely unresolved. To address this, we performed a comparative genomic analysis between a highly virulent strain Pta6605 and a less virulent strain Pta7375. Despite high overall genome similarity, we identified key single-nucleotide polymorphisms, including premature stop-codon mutations in seven open reading frames in Pta7375. Notably, point mutations in two regulatory genes, such as fleQ, which encodes a transcription factor essential for flagellar biogenesis and biofilm formation, and gcbB, which encodes a GGDEF domain-containing diguanylate cyclase responsible for cyclic dimeric guanosine monophosphate (c-di-GMP) synthesis, were implicated in virulence disparity. Functional analyses using deletion and locus replacement mutants in the Pta6605 background revealed that the disruption of fleQ markedly reduced motility, flagellin production, c-di-GMP accumulation, biofilm formation and virulence level mirroring the Pta7375 phenotype. The gcbB replacement mutant showed reduced disease symptom development, although c-di-GMP levels remained comparable to the Pta6605 wild type. Locus replacement between strains confirmed that a point mutation in fleQ was the primary driver of reduced motility and flagellin expression in Pta7375. These findings indicate that the reduced virulence of Pta7375 is associated with impaired regulation of flagella-related genes and disruption of the FleQ-mediated c-di-GMP signalling, underscoring the value of comparative genomics in disentangling the complex regulatory networks that govern virulence in plant pathogens.

Plants typically encode multiple ubiquitin-activating enzymes (E1s or UBAs), but their functional equivalence or divergence remains unclear. Here, we demonstrate that the two tomato (Solanum lycopersicum) E1s, SlUBA1 and SlUBA2, differentially regulate development and immunity. Knockdown of SlUBA1 or SlUBA2 caused distinct growth and developmental defects in tomato, while silencing both genes resulted in severe abnormalities, rapid etiolation, and plant death within 5-7 weeks. Notably, silencing SlUBA2, but not SlUBA1, compromised plant immunity against the bacterial pathogen Pseudomonas syringae pv. tomato (Pst). SlUBA1 and SlUBA2 exhibited distinct charging efficiencies for E2s from groups IV (SlUBC32/33/34), V (SlUBC7/14/35/36), VI (SlUBC4/5/6/15) and XII (SlUBC22), with SlUBA2 showing significantly higher efficiency. Swapping the C-terminal ubiquitin-folding domains (UFDs) between SlUBA1 and SlUBA2 largely reversed their E2-charging efficiency for these groups. Furthermore, mutating a key residue (SlUBA2^Q1009) in the UFD or deleting a conserved 13-amino-acid sequence unique to group V E2s altered the E2-charging profiles of both E1s. These findings suggest dual ubiquitin-activating systems (DUAS) operate in tomato. Given the established role of group IV E2s in plant immunity against Pst, the SlUBA2-group IV E2 module likely plays a central role in modulating host defence. Similarly, the Arabidopsis E1s, AtUBA1 and AtUBA2, differentially charge homologues of tomato group IV E2s, suggesting a conserved mechanism by which plant E1s fulfil distinct physiological roles.

Emerging pathogen races spreading via long-distance migration increasingly threaten global agricultural ecosystems. Understanding how pathogens migrate and adapt to new hosts via virulence evolution is crucial for developing strategies to mitigate future crop damage. Here we performed biosurveillance of Puccinia polysora, a global fungal pathogen causing southern corn rust (SCR), across China, Thailand and the Philippines. By analysing 193 field transcriptomic data, we detected both epidemic and endemic lineages co-circulating in each country and elucidated the crucial role of host selection in driving the diversification of endemic lineages. Gene flow assessments and trajectory tracking indicated that the SCR infection source in northern China is likely of domestic origin and pathogen migration from the Philippines/Thailand into China is restricted to Hainan, coastal Guangdong and southern Yunnan. We detected country-specific variants in 32 effector genes, with AvrRppC exhibiting the strongest positive selection. A phylogenetically distinct Luzon Island lineage (Philippines), carrying a novel AvrRppC allele capable of overcoming RppC-mediated resistance and represents a potentially invasive threat. Finally, we reviewed the global migration history of P. polysora in light of our findings. Our work represents the first step toward establishing an international surveillance network for P. polysora and emphasised a comprehensive control strategy integrating local governance and invasion prevention of international races.

Plant inner nuclear membrane (INM) Sad1/UNC-84 (SUN) proteins are essential for maintaining nuclear morphology, positioning and gene expression during development and environmental stress conditions. Recent studies suggest their involvement in symbiosis and pathogen defence, but their precise role in plant immunity remains unclear. Given the importance of nuclear dynamics during plant-pathogen interactions, understanding the function of SUN proteins in immune signalling is essential. Here, we identify and characterise the pea (Pisum sativum) C-terminal SUN. Using knockdown (KD) and overexpression (OE) strategies in pea and/or Arabidopsis, we demonstrate that PsSUN localises to the INM and regulates pathogen-induced nuclear positioning, nuclear morphology and defence gene expression. PsSUN-KD increased nuclear circularity and sphericity, impaired nuclear relocation to the fungal penetration site, and inhibited powdery mildew growth. PsSUN-OE deformed the nuclear envelope (NE) and enhanced defence gene expression and pathogen resistance. PsSUN-OE also increased plant abiotic stress-responsive gene expression and abscisic acid sensitivity. Furthermore, we demonstrate that interactions between PsSUN and the Arabidopsis lamin-like protein KAKU4 likely influence both their localisation at the nuclear periphery and the architecture of the NE, with the extent of these effects depending on the expression levels of the two proteins. Our results suggest that SUN and nuclear lamina coordinately regulate plant NE architecture and stress responses.

Seed immune responses are an underexplored area in host-pathogen interactions, leaving seed-pathogen interactions poorly understood despite their considerable economic impact. This study examined tomato seed defences by assessing the antimicrobial activity (AA) of seed exudates during germination. Results showed genotype-dependent and constitutive defence responses from seeds showing AA in exudates. Seed priming with a panel of elicitors such as methyl jasmonate (MeJA) enhanced AA in certain genotypes, highlighting an inducible defence response. Both constitutive and inducible (elicitor-dependent) seed defences were genotype-dependent and more effective against the non-host pathogen Alternaria brassicicola (Abra43), while host pathogens seemed resistant to exudates' AA, suggesting that they developed strategies to neutralise exudates' AA. Multi-omic analyses revealed distinct hormonal and molecular pathways involved in constitutive and inducible defences. By characterising exudates and correlating genotype- and elicitor-specific AA, candidate antimicrobial compounds were identified. As proof of concept, we functionally validated the AA of a putative defensin (Solyc07g007755) whose expression was highly correlated with the observed AA of the seed exudate against Abra43, demonstrating the potential of our dataset for the development of phytosanitary strategies to protect seeds during germination.

Studies have demonstrated microRNA398 (miR398) hyperaccumulation in plant species infected with viruses; however, its role in a viral context remains unexplored. Here, we identified cassava (Mes)-miR398 as a regulatory miRNA responsive to cassava common mosaic virus (CsCMV) infection through small-RNA analysis. Mes-miR398 targets Dirigent (Dir; Manes.05G165700.1) associated with disease resistance. Transgenic cassava lines overexpressing Mes-miR398 (OE398) showed downregulation of the Dir gene during CsCMV infection. A dual-luciferase reporter assay confirmed the direct targeting of the Dir gene by miR398. Interestingly, OE398 lines exhibited enhanced vegetative growth. However, CsCMV accumulation was significantly higher in OE398-CsCMV and Dir-silenced (SDir)-CsCMV lines and reduced in Dir-overexpressing (OEDir-CsCMV) lines, indicating a negative regulatory role of the Mes-miR398/Dir module in antiviral defence. Transmission electron microscopy revealed a reduction in cell wall thickness in CsCMV-infected plants compared with healthy controls. A similar decrease was observed in SDir lines, whereas OEDir lines maintained greater wall thickness. Furthermore, lignin content was significantly reduced in SDir lines relative to OEDir lines. Histochemical staining with Toluidine Blue O and Safranin O-Fast Green supported these findings, showing increased lignification in OEDir lines and reduced lignification in SDir lines. Subcellular localisation demonstrated that the Dir protein localises to the cell membrane, suggesting a role in regulating the cell wall membrane. These results revealed that the mes-miR398/Dir regulatory module negatively affects cassava resistance to CsCMV by altering cell wall lignification. This study is the first to identify miR398 as a regulator of a Dir gene and provides critical insights into the molecular interactions between cassava and CsCMV.

Rising global temperatures exacerbate the severity of crop diseases, threatening global agricultural production. Citrus yellow mosaic virus (CYMV) is one of the pathogens that seriously threaten citrus production, the world's largest fruit industry. However, the molecular mechanisms underlying CYMV-citrus interactions at high temperatures remain poorly understood. Over a 1-year observation period, this study found elevated temperatures increased CYMV accumulation in Madam Vinous sweet orange. Controlled experiments comparing 25°C and 37°C conditions further validated this phenomenon, with significantly higher viral titres observed under high-temperature treatments (37°C). Subsequent transcriptomic analysis revealed that the transcription factor CsWRKY76 and the pathogenesis-related gene CsPR4A were significantly downregulated in sweet orange infected with CYMV at 37°C. CsWRKY76 could directly bind to the CsPR4A promoter, thereby positively regulating CsPR4A transcription. Overexpression of CsWRKY76 or CsPR4A in transgenic citrus hairy roots significantly suppressed CYMV accumulation, while RNAi-mediated silencing of either gene promoted viral accumulation, indicating that both genes were positive regulators of citrus immunity. Overexpression of CsWRKY76 increased hydrogen peroxide content in transgenic citrus hairy roots while upregulating CsPAL2 and CsCOMT1 (involved in phenylpropanoid metabolism). This study elucidates the molecular mechanism by which high temperature suppresses the immune function of the CsWRKY76-CsPR4A modules and thereby promotes the accumulation of CYMV. Our results provide a theoretical basis for developing high-temperature-resistant disease control strategies in citrus.

Hydrogen sulphide (H₂S), a gaseous signalling molecule, plays a multifaceted role in plant physiology by enhancing adaptability to environmental stresses. However, the regulatory mechanism of symbiotic nitrogen (N) fixation by H₂S in indeterminate nodules of woody legumes remains unclear. In this study, we investigated the mechanism by which H₂S promotes nodulation and N fixation in the woody legume Robinia pseudoacacia. Exogenous H₂S significantly enhanced rhizobium infection, nodule formation and nitrogenase activity, demonstrating its positive role in the symbiotic process. Transcriptomic analysis of roots and nodules revealed that H₂S signalling modulates auxin metabolism, particularly through the regulation of indole-3-acetic acid (IAA) homeostasis. H₂S was found to promote free IAA accumulation and reduce IAA conjugation (IAA-Asp and IAA-Glu). Further investigation revealed that H₂S directly targets GH3.1, a key IAA-amido synthetase responsible for IAA conjugation. Specifically, H₂S mediated persulfidation at Cys304 of GH3.1, inhibiting its enzymatic activity and preventing IAA inactivation. This modification was confirmed by LC-MS/MS, UPLC-ESI-MS/MS and site-directed mutagenesis. This post-translational modification maintained active IAA levels, facilitating early nodule development. These findings highlight the active role of H₂S in regulating IAA homeostasis, thereby enhancing indeterminate nodule formation and N fixation through persulfidation of the Cys304 residue of GH3.1 in R. pseudoacacia.

The co-infection of maize chlorotic mottle virus (MCMV) and sugarcane mosaic virus (SCMV) causes maize lethal necrosis (MLN), which seriously affects the yield and quality of maize. Ubiquitination is one of the most important protein post-translational modifications. However, the role of ubiquitination modification in regulating maize resistance to viral infection remains largely unknown. In this study, we found that the ubiquitination levels in SCMV- and/or MCMV-infected maize plants were higher than that in the non-infected maize plants. Ubiquitinome and proteome analyses of the above maize plants revealed that most down-regulated differentially accumulated proteins that possessed up-regulated lysine ubiquitination sites were mainly involved in photosynthesis, fructose and mannose metabolism, and glyoxylate and dicarboxylate metabolism. Functional analyses of three DAPs involved in glyoxylate metabolism demonstrated that silencing ZmGOX1 facilitated SCMV and MCMV single and co-infection, while knockdown of ZmHPR1 or ZmHPR2 suppressed viral infections. Moreover, overexpression of ZmGOX1 and its mutants at Kub sites enhanced maize resistance to SCMV infection. We also found that exogenous application of sodium sulphide could up-regulate the expression of ZmGOX1 and effectively inhibit viral infections. These findings provide novel insights into the roles of ubiquitination in the regulation of maize resistance to viral infection.