Abscisic-acid-responsive StlncRNA13558 induces StPRL expression to increase potato resistance to Phytophthora infestans infection.

Late blight, caused by Phytophthora infestans, is one of the most serious diseases affecting potatoes (Solanum tuberosum L.). Long non-coding RNAs (lncRNAs) are transcripts with a length of more than 200 nucleotides that have no protein-coding potential. Few studies have been conducted on lncRNAs related to plant immune regulation in plants, and the molecular mechanisms involved in this regulation require further investigation. We identified and screened an lncRNA that specifically responds to P. infestans infection, namely, StlncRNA13558. P. infestans infection activates the abscisic acid (ABA) pathway, and ABA induces StlncRNA13558 to enhance potato resistance to P. infestans. StlncRNA13558 positively regulates the expression of its co-expressed PR-related gene StPRL. StPRL promotes the accumulation of reactive oxygen species and transmits a resistance response by affecting the salicylic acid hormone pathway, thereby enhancing potato resistance to P. infestans. In summary, we identified the potato late blight resistance lncRNA StlncRNA13558 and revealed its upstream and downstream regulatory relationship of StlncRNA13558. These results improve our understanding of plant-pathogen interactions' immune mechanism and elucidate the response mechanism of lncRNA-target genes regulating potato resistance to P. infestans infection.

Interactions of Tomato Chlorosis Virus p27 Protein with Tomato Catalase Are Involved in Viral Infection.

Tomato chlorosis virus (ToCV) severely threatens tomato production worldwide. P27 is known to be involved in virion assembly, but its other roles in ToCV infection are unclear. In this study, we found that removal of p27 reduced systemic infection, while ectopic expression of p27 promoted systemic infection of potato virus X in Nicotiana benthamiana. We determined that Solanum lycopersicum catalases (SlCAT) can interact with p27 in vitro and in vivo and that amino acids 73 to 77 of the N-terminus of SlCAT represent the critical region for their interaction. p27 is distributed in the cytoplasm and nucleus, and its coexpression with SlCAT1 or SlCAT2 changes its distribution in the nucleus. Furthermore, we found that silencing of SlCAT1 and SlCAT2 can promote ToCV infection. In conclusion, p27 can promote viral infection by binding directly to inhibit anti-ToCV processes mediated by SlCAT1 or SlCAT2.

Tomato chlorosis virus p22 interacts with NbBAG5 to inhibit autophagy and regulate virus infection.

Tomato chlorosis virus (ToCV) is a member of the genus Crinivirus in the family Closteroviridae. It has a wide host range and wide distribution, causing serious harm to the vegetable industry. The autophagy pathway plays an important role in plant resistance to virus infection. Viruses and plant hosts coevolve in defence and antidefence processes around autophagy. In this study, the interaction between ToCV p22 and Nicotiana benthamiana B-cell lymphoma2-associated athanogenes5 Nicotiana benthamiana (NbBAG5) was examined. Through overexpression and down-regulation of NbBAG5, results showed that NbBAG5 could negatively regulate ToCV infection. NbBAG5 was found to be localized in mitochondria and can change the original localization of ToCV p22, which is colocalized in mitochondria. NbBAG5 inhibited the expression of mitophagy-related genes and the number of autophagosomes, thereby regulating viral infection by affecting mitophagy. In summary, this study demonstrated that ToCV p22 affects autophagy by interacting with NbBAG5, established the association between viral infection, BAG proteins family, and the autophagy pathway, and explained the molecular mechanism by which ToCV p22 interacts with NbBAG5 to inhibit autophagy to regulate viral infection.

Potential risk of plant viruses entering disease cycle in surface water in protected vegetable growing areas of Eastern China.

With the expansion of protected vegetable growing areas (PVGAs), viral plant diseases have become more prevalent, causing severe economic losses to the vegetable production industry in China. At present, researches on plant viruses mainly focus on plants, but there is only a few reports on the species of viruses in surface water from PVGAs. The surface water samples in PVGAs are representative to a certain extent, which has an important reference value for studying the characteristics of plant viruses in surface water. The purpose of this study was to identify the diversity and the possibility of entering disease infection cycle of plant viruses in water samples collected from PVGAs in eastern China. A total of 144 water samples were collected, and eight plant viruses including tobacco mosaic virus (TMV, 8.33%), cucumber green mottle mosaic virus (CGMMV, 33.33%), pepper mild mottle virus (PMMoV, 6.94%), cucumber mosaic virus (CMV, 0.69%), tomato masaic virus (ToMV, 3.47%), tomato mottle mosaic virus (ToMMV, 0.69%), tomato chlorosis virus (ToCV, 4.17%), and tomato yellow leaf curl virus (TYLCV, 5.56%) were examined using RT-PCR and PCR. The species of viruses in surface water varied greatly by location. CGMMV, TMV, ToCV, ToMV, ToMMV, and TYLCV were identified in Shandong, a northern part of Eastern China, whereas only PMMoV was found in Shanghai, a southern part of Eastern China. After healthy tobacco plants were inoculated with the concentrated solutions of TMV, ToMV, CGMMV, and PMMoV, could cause disease in healthy tobacco, indicating that the plant viruses in the concentrated solution have the infectivity, and the plant viruses in surface water have the possibility of entering the infection cycle of disease. The results will improve the understanding of the potential risks of waterborne disease transmission.

Potato (Solanum tuberosum L.) non-specific lipid transfer protein StLTP6 promotes viral infection by inhibiting virus-induced RNA silencing.

MAIN CONCLUSION: For the first time it is reported that members of the nsLTP protein family could promote viral infection by inhibiting virus-induced RNA silencing. Non-specific lipid transfer proteins (nsLTPs) are a class of soluble proteins with low relative molecular weight and widely present in higher plants. The role of nsLTPs in biotic and abiotic stresses has been studied, but no report has shown that nsLTPs play a role in the process of viral infection. We report the function and mechanism of the classical nsLTP protein StLTP6 in viral infection. We found that StLTP6 expression was remarkably upregulated in potato infected with potato virus Y and potato virus S. The infection efficiency and virus content of StLTP6-overexpressed potato and Nicotiana benthamiana were remarkable increased. Further study found that the overexpression of StLTP6 inhibited the expression of multiple genes in the RNA silencing pathway, thereby inhibiting virus-induced RNA silencing. This result indicated that StLTP6 expression was induced during viral infection to inhibit the resistance of virus-induced RNA silencing and promote viral infection. In summary, we reported the role of StLTP6 in viral infection, broadening the biological function range of the nsLTP family and providing valuable information for the study of viral infection mechanism.

WIPK-NtLTP4 pathway confers resistance to Ralstonia solanacearum in tobacco.

KEY MESSAGE: WIPK-NtLTP4 module improves the resistance to R. solanacearum via upregulating the expression of defense-related genes, increasing the antioxidant enzyme activity, and promoting stomatal closure in tobacco. Lipid transfer proteins (LTPs) are a class of small lipid binding proteins that play important roles in biotic and abiotic stresses. The previous study revealed that NtLTP4 positively regulates salt and drought stresses in Nicotiana tabacum. However, the role of NtLTP4 in biotic stress, especially regarding its function in disease resistance remains unclear. Here, the critical role of NtLTP4 in regulating resistance to Ralstonia solanacearum (R. solanacearum), a causal agent of bacterial wilt disease in tobacco, was reported. The NtLTP4-overexpressing lines markedly improved the resistance to R. solanacearum by upregulating the expression of defense-related genes, increasing the antioxidant enzyme activity, and promoting stomatal closure. Moreover, NtLTP4 interacted with wound-induced protein kinase (WIPK; a homolog of MAPK3 in tobacco) and acted in a genetically epistatic manner to WIPK in planta. WIPK could directly phosphorylate NtLTP4 to positively regulate its protein abundance. Taken together, these results broaden the knowledge about the functions of the WIPK-NtLTP4 module in disease resistance and may provide valuable information for improving tobacco plant tolerance to R. solanacearum.

Global transcriptome analyses reveal the molecular signatures in the early response of potato (Solanum tuberosum L.) to Phytophthora infestans, Ralstonia solanacearum, and Potato virus Y infection.

MAIN CONCLUSION: Specific and common genes including transcription factors, resistance genes and pathways were significantly induced in potato by Phytophthora infestans, Ralstonia solanacearum, and Potato virus Y infection. The three major pathogens, namely, Phytophthora infestans, Ralstonia solanacearum, and Potato virus Y, can cause late blight, bacterial wilt, and necrotic ringspot, respectively, and thus severely reduce the yield and quality of potatoes (Solanum tuberosum L.). This study was the first to systematically analyze the relationship between transcriptome alterations in potato infected by these pathogens at the early stages. A total of 75,500 unigenes were identified, and 44,008 were annotated into 5 databases, namely, non-redundant (NR), Swiss-Prot protein, clusters of orthologous groups for eukaryotic complete genomes (KOG), Gene Ontology (GO), and Kyoto Encyclopedia of Genes and Genomes (KEGG) databases. A total of 6945 resistance genes and 11,878 transcription factors (TFs) were identified from all transcriptome data. Differential expression analysis revealed that 13,032 (9490 specifics), 9877 (6423 specifics), and 6661 (4144 specifics) differentially expressed genes (DEGs) were generated from comparisons of the P. infestans/control (Pi vs. Pi-CK), R. solanacearum/control (Rs vs. Rs-CK), and PVY/control (PVY vs. PVY-CK) treatments, respectively. The specific DEGs from the 3 comparisons were assigned to 13 common pathways, such as biosynthesis of amino acids, plant hormone signal transduction, carbon metabolism, and starch and sucrose metabolism. Weighted Gene Co-Expression Network Analysis (WGCNA) identified many hub unigenes, of which several unigenes were reported to regulate plant immune responses, such as FLAGELLIN-SENSITIVE 2 and chitinases. The present study provide crucial systems-level insights into the relationship between transcriptome changes in potato infected with the three pathogens. Moreover, this study presents a theoretical basis for breeding broad-spectrum and specific pathogen-resistant cultivars.