Molecular plant pathology最新文献

Persistent plant viruses are widespread in natural ecosystems. However, little is known about why persistent infection with these viruses may cause little or no harm to their host. Here, we discovered a new polerovirus that persistently infected wild rice plants by deep sequencing and assembly of virus-derived small-interfering RNAs (siRNAs). The new virus was named Rice tiller inhibition virus 2 (RTIV2) based on the symptoms developed in cultivated rice varieties following Agrobacterium-mediated inoculation with an infectious RTIV2 clone. We showed that RTIV2 infection induced antiviral RNA interference (RNAi) in both the wild and cultivated rice plants as well as Nicotiana benthamiana. It is known that virulent virus infection in plants depends on effective suppression of antiviral RNAi by viral suppressors of RNAi (VSRs). Notably, the P0 protein of RTIV2 exhibited weak VSR activity and carries alanine substitutions of two amino acids broadly conserved among diverse poleroviruses. Mixed infection with umbraviruses enhanced RTIV2 accumulation and/or enabled its mechanical transmission in N. benthamiana. Moreover, replacing the alanine at either one or both positions of RTIV2 P0 enhanced the VSR activity in a co-infiltration assay, and RTIV2 mutants carrying the corresponding substitutions replicated to significantly higher levels in both rice and N. benthamiana plants. Together, our findings show that as a persistent plant virus, RTIV2 carries specific mutations in its VSR gene to weaken viral suppression of antiviral RNAi. Our work reveals a new strategy for persistent viruses to maintain long-term infection by weak suppression of the host defence response.

Autophagy, an intracellular degradation process, has emerged as a crucial innate immune response against various plant pathogens, including viruses. Tomato spotted wilt orthotospovirus (TSWV) is a highly destructive plant pathogen that infects over 1000 plant species and poses a significant threat to global food security. However, the role of autophagy in defence against the TSWV pathogen, and whether the virus counteracts this defence, remains unknown. In this study, we report that autophagy plays an important role in antiviral defence against TSWV infection; however, this autophagy-mediated defence is counteracted by the viral effector NSs. Transcriptome profiling revealed the up-regulation of autophagy-related genes (ATGs) upon TSWV infection. Blocking autophagy induction by chemical treatment or knockout/down of ATG5/ATG7 significantly enhanced TSWV accumulation. Notably, the TSWV nucleocapsid (N) protein, a major component of the viral replication unit, strongly induced autophagy. However, the TSWV nonstructural protein NSs was able to effectively suppress N-induced autophagy in a dose-dependent manner. Further investigation revealed that NSs inhibited ATG6-mediated autophagy induction. These findings provide new insights into the defence role of autophagy against TSWV, a representative segmented negative-strand RNA virus, as well as the tospoviral pathogen counterdefence mechanism.

Cassava starch is a widely used raw material for industrial production and food source for people. However, cassava bacterial blight (CBB) caused by Xanthomonas axonopodis pv. manihotis (Xam) results in severe yield losses and is the most destructive bacterial disease in all worldwide cassava-growing regions. Xam11 is a highly pathogenic subspecies from China that infects the Chinese local cassava South China No. 8 (SC8) cultivar with marked symptoms. This study showed that the transcription activator-like effector TALE20_Xam11 of Xam11 strain regulates the expression of disease-susceptibility gene MeSWEET10a by binding to the EBE_TALE20 region of the MeSWEET10a promoter in cassava cultivar SC8. CRISPR/Cas9-generated mutations of the EBE_TALE20 region resulted in a significant reduction in MeSWEET10a expression after infection by Xam11, correlating with reduced disease symptoms, smaller lesion sizes and decreased bacterial proliferation compared with the wild type. Importantly, the edited plants maintained normal growth, development and yield characteristics under greenhouse conditions. The results lay a research foundation for breeding resistant cassava cultivar SC8 to bacterial blight.

Pear chlorotic leaf spot-associated virus (PCLSaV) is a newly described emaravirus that infects pear trees. The virus genome consists of at least five single-stranded, negative-sense RNAs. The P5 encoded by RNA5 is unique to PCLSaV. In this study, the RNA silencing suppression (RSS) activity of P5 and its subcellular localization were determined in Nicotiana benthamiana plants by Agrobacterium tumefaciens-mediated expression assays and green fluorescent protein RNA silencing induction. Protein P5 partially suppressed local RNA silencing, strongly suppressed systemic RNA silencing and triggered reactive oxygen species accumulation. The P5 self-interacted and showed subcellular locations in plasmodesmata, endoplasmic reticulum and nucleus. Furthermore, P5 rescued the cell-to-cell movement of a movement defective mutant PVXΔP25 of potato virus X (PVX) and enhanced the pathogenicity of PVX. The N-terminal 1-89 amino acids of the P5 were responsible for the self-interaction ability and RSS activity, for which the signal peptide at positions 1-19 was indispensable. This study demonstrated the function of an emaravirus protein as a pathogenic factor suppressing plant RNA silencing to enhance virus infection and as an enhancer of virus movement.

Positive-sense RNA viruses remodel cellular cytoplasmic membranes as the membranous sources for the formation of viral replication organelles (VROs) for viral genome replication. In plants, they traffic through plasmodesmata (PD), plasma membrane-lined pores enabling cytoplasmic connections between cells for intercellular movement and systemic infection. In this study, we employed turnip mosaic virus (TuMV), a plant RNA virus to investigate the involvement of RTNLB3 and RTNLB6, two ER (endoplasmic reticulum) membrane-bending, PD-located reticulon-like (RTNL) non-metazoan group B proteins (RTNLBs) in viral infection. We show that RTNLB3 interacts with TuMV 6K2 integral membrane protein and RTNLB6 binds to TuMV coat protein (CP). Knockdown of RTNLB3 promoted viral infection, whereas downregulation of RTNLB6 restricted viral infection, suggesting that these two RTNLs play contrasting roles in TuMV infection. We further demonstrate that RTNLB3 targets the α-helix motif ⁴²LRKSM⁴⁶ of 6K2 to interrupt 6K2 self-interactions and compromise 6K2-induced VRO formation. Moreover, overexpression of AtRTNLB3 apparently promoted the selective degradation of the ER and ER-associated protein calnexin, but not 6K2. Intriguingly, mutation of the α-helix motif of 6K2 that is required for induction of VROs severely affected 6K2 stability and abolished TuMV infection. Thus, RTNLB3 attenuates TuMV replication, probably through the suppression of 6K2 function. We also show that RTNLB6 promotes viral intercellular movement but does not affect viral replication. Therefore, the proviral role of RTNLB6 is probably by enhancing viral cell-to-cell trafficking. Taken together, our data demonstrate that RTNL family proteins may play diverse complex, even opposite, roles in viral infection in plants.

MicroRNA-like RNAs (milRNAs) play a significant role in the infection process by plant-pathogenic fungi. However, the specific functions and regulatory mechanisms of fungal milRNAs remain insufficiently elucidated. This study investigated the function of Foc-milR138, an infection-induced milRNA secreted by Fusarium oxysporum f. sp. cubense (Foc), which is the causal agent of Fusarium wilt of banana. Initially, through precursor gene knockout and phenotypic assessments, we confirmed that Foc-milR138 acts as a virulent milRNA prominently upregulated during the early stages of Foc infection. Subsequent bioinformatic analyses and transient expression assays in Nicotiana benthamiana leaves identified a host receptor-like kinase gene, MaLYK3, as the direct target of Foc-milR138. Functional investigations of MaLYK3 revealed its pivotal role in triggering immune responses of N. benthamiana by upregulating a suite of resistance genes, bolstering reactive oxygen species (ROS) accumulation and callose deposition, thereby fortifying disease resistance. This response was markedly subdued upon co-expression with Foc-milR138. Expression pattern analysis further verified the specific suppression of MaLYK3 by Foc-milR138 during the early root infection by Foc. In conclusion, Foc secretes a virulent milRNA (Foc-milR138) to enter the host banana cells and inhibit the expression of the plant surface receptor-like kinase MaLYK3, subverting the disease resistance activated by MaLYK3, and ultimately facilitating pathogen invasion. These findings shed light on the roles of fungal milRNAs and their targets in resistance and pathogenicity, offering promising avenues for the development of disease-resistant banana cultivars.

Following the invasion by the pine wood nematode (PWN) into north-east China, a notable disparity in susceptibility was observed among Pinaceae species. Larix olgensis exhibited marked resilience and suffered minimal fatalities, while Pinus koraiensis experienced significant mortality due to PWN infection. Our research demonstrated that the PWNs in L. olgensis showed a 13.43% reduction in lipid content compared to P. koraiensis (p < 0.05), which was attributable to the accumulation of caffeic acid in L. olgensis. This reduction in lipid content was correlated with a decreased overwintering survival of PWNs. The diminished lipid reserves were associated with substantial stunting in PWNs, including reduced body length and maximum body width. The result suggests that lower lipid content is a major factor contributing to the lower overwintering survival rate of PWNs in L. olgensis induced by caffeic acid. Through verification tests, we concluded that the minimal fatalities observed in L. olgensis could be attributed to the reduced overwintering survival of PWNs, a consequence of caffeic acid-induced stunting. This study provides valuable insights into PWN-host interactions and suggests that targeting caffeic acid biosynthesis pathways could be a potential strategy for managing PWN in forest ecosystems.

Vector-borne bacterial pathogens cause devastating plant diseases that cost billions of dollars in crop losses worldwide. These pathogens have evolved to be host- and vector-dependent, resulting in a reduced genome size compared to their free-living relatives. All known vector-borne bacterial plant pathogens belong to four different genera: 'Candidatus Liberibacter', 'Candidatus Phytoplasma', Spiroplasma and Xylella. To protect themselves against pathogens, plants have evolved pattern recognition receptors that can detect conserved pathogen features as non-self and mount an immune response. To gain an understanding of how vector-borne pathogen features are perceived in plants, we investigated three proteinaceous features derived from cold shock protein (csp22), flagellin (flg22) and elongation factor Tu (elf18) from vector-borne bacterial pathogens as well as their closest free-living relatives. In general, vector-borne pathogens have fewer copies of genes encoding flagellin and cold shock protein compared to their closest free-living relatives. Furthermore, epitopes from vector-borne pathogens were less likely to be immunogenic compared to their free-living counterparts. Most Liberibacter csp22 and elf18 epitopes do not trigger plant immune responses in tomato or Arabidopsis. Interestingly, csp22 from the citrus pathogen 'Candidatus Liberibacter asiaticus' triggers immune responses in solanaceous plants, while csp22 from the solanaceous pathogen 'Candidatus Liberibacter solanacearum' does not. Our findings suggest that vector-borne plant pathogenic bacteria evolved to evade host recognition.

Zymoseptoria tritici is the most economically significant fungal pathogen of wheat in Europe. However, despite the importance of this pathogen, the molecular interactions between pathogen and host during infection are not well understood. Herein, we describe the use of two libraries of cloned Z. tritici effectors that were screened to identify effector candidates with putative pathogen-associated molecular pattern (PAMP)-triggered immunity (PTI)-suppressing activity. The effectors from each library were transiently expressed in Nicotiana benthamiana, and expressing leaves were treated with bacterial or fungal PAMPs to assess the effectors' ability to suppress reactive oxygen species (ROS) production. From these screens, numerous effectors were identified with PTI-suppressing activity. In addition, some effectors were able to suppress cell death responses induced by other Z. tritici secreted proteins. We used structural prediction tools to predict the putative structures of all of the Z. tritici effectors and used these predictions to examine whether there was enrichment of specific structural signatures among the PTI-suppressing effectors. From among the libraries, multiple members of the killer protein-like 4 (KP4) and killer protein-like 6 (KP6) effector families were identified as PTI suppressors. This observation is intriguing, as these protein families were previously associated with antimicrobial activity rather than virulence or host manipulation. This data provides mechanistic insight into immune suppression by Z. tritici during infection and suggests that, similar to biotrophic pathogens, this fungus relies on a battery of secreted effectors to suppress host immunity during early phases of colonization.

ATP-binding cassette (ABC) transporters hydrolyse ATP to transport various substrates. Previous studies have shown that ABC transporters are responsible for transporting plant hormones and heavy metals, thus contributing to plant immunity. Herein, we identified a wheat G-type ABC transporter, TaABCG2-5B, that responds to salicylic acid (SA) treatment and is induced by Fusarium graminearum, the primary pathogen causing Fusarium head blight (FHB). The loss-of-function mutation of TaABCG2-5B (ΔTaabcg2-5B) reduced SA accumulation and increased susceptibility to F. graminearum. Conversely, overexpression of TaABCG2-5B (OE-TaABCG2-5B) exerted the opposite effect. Quantification of intracellular SA in ΔTaabcg2-5B and OE-TaABCG2-5B protoplasts revealed that TaABCG2-5B acts as an importer, facilitating the transport of SA into the cytoplasm. This role was further confirmed by Cd²⁺ absorption experiments in wheat roots, indicating that TaABCG2-5B also participates in Cd²⁺ transport. Thus, TaABCG2-5B acts as an importer and is crucial for transporting multiple substrates. Notably, the homologous gene TaABCG2-5A also facilitated Cd²⁺ uptake in wheat roots but did not significantly influence SA accumulation or FHB resistance. Therefore, TaABCG2 could be a valuable target for enhancing wheat tolerance to Cd²⁺ and improving FHB resistance.