Plant diseases caused by fungi and oomycetes pose an increasing threat to food security and ecosystem health worldwide. These filamentous pathogens, while taxonomically distinct, modulate host defense responses by secreting effectors, which are typically identified based on the presence of signal peptides. Here we show that Phytophthora sojae and Verticillium dahliae secrete isochorismatases (PsIsc1 and VdIsc1, respectively) that are required for full pathogenesis. PsIsc1 and VdIsc1 can suppress salicylate-mediated innate immunity in planta and hydrolyse isochorismate in vitro. A conserved triad of catalytic residues is essential for both functions. Thus, the two proteins are isochorismatase effectors that disrupt the plant salicylate metabolism pathway by suppressing its precursor. Furthermore, these proteins lack signal peptides, but exhibit characteristics that lead to unconventional secretion. Therefore, this secretion pathway is a novel mechanism for delivering effectors and might play an important role in host–pathogen interactions.

Recently, a large number of long noncoding RNAs (lncRNAs) have emerged as important regulators of many biological processes in animals and plants. However, how lncRNAs function during plant DNA virus infection is largely unknown. We performed strand-specific paired-end RNA sequencing of tomato samples infected with Tomato yellow leaf curl virus (TYLCV) with three biological replicates. Overall, we predicted 1565 lncRNAs including long intergenic ncRNAs (lincRNAs) and natural antisense transcripts (lncNATs) and definitively identified lnRNAs that are involved in TYLCV infection by virus-induced gene silencing (VIGS). We also verified the functions of a set of lncRNAs that were differentially expressed between 0 and 7 days post inoculation (dpi). More importantly, we found that several lncRNAs acted as competing endogenous target mimics (eTMs) for tomato microRNAs involved in the TYLCV infection. These results provide new insight into lncRNAs involved in the response to TYLCV infection that are important components of the TYLCV network in tomatoes.

Verticillium wilt caused by soilborne fungus Verticillium dahliae could significantly reduce cotton yield. Here, we cloned a tomato Ve homologous gene, Gbve1, from an island cotton cultivar that is resistant to Verticillium wilt. We found that the Gbve1 gene was induced by V. dahliae and by phytohormones salicylic acid, jasmonic acid, and ethylene, but not by abscisic acid. The induction of Gbve1 in resistant cotton was quicker and stronger than in Verticillium-susceptible upland cotton following V. dahliae inoculation. Gbve1 promoter-driving GUS activity was found exclusively in the vascular bundles of roots and stems of transgenic Arabidopsis. Virus-induced silencing of endogenous genes in resistant cotton via targeting a fragment of the Gbve1 gene compromised cotton resistance to V. dahliae. Furthermore, we transformed the Gbve1 gene into Arabidopsis and upland cotton through Agrobacterium-mediated transformation. Overexpression of the Gbve1 gene endowed transgenic Arabidopsis and upland cotton with resistance to high aggressive defoliating and non-defoliating isolates of V. dahliae. And HR-mimic cell death was observed in the transgenic Arabidopsis. Our results demonstrate that the Gbve1 gene is responsible for resistance to V. dahliae in island cotton and can be used for breeding cotton varieties that are resistant to Verticillium wilt.

Drought stress negatively affects plant growth and limits plant productivity. Genes functioning in plant responses to drought stress are essential for the development of drought-tolerant crops. Here, we report that an R2R3-type MYB transcription factor gene in Gossypium barbadense, GbMYB5, confers drought tolerance in cotton and transgenic tobacco. Virus-induced gene silencing of GbMYB5 compromised the tolerance of cotton plantlets to drought stress and reduced the post-rewatering water recovery survival rate to 50% as compared with the 90% survival rate in the wild type (WT). Silencing GbMYB5 decreased proline content and antioxidant enzyme activities and increased malondialdehyde (MDA) content in cotton under drought stress. The expression levels of drought-inducible genes NCED3, RD22 and RD26 were not affected by the silencing of GbMYB5. However, GbMYB5-overexpressing tobacco lines displayed hypersensitivity to ABA and improved survival rates as well as reduced water loss rates under drought stress. Furthermore, stomatal size and the rate of opening of stomata were markedly decreased in transgenic tobacco. The overexpression of GbMYB5 enhanced the accumulation of proline and antioxidant enzymes while it reduced production of MDA in transgenic tobacco as compared with the WT under drought stress. The transcript levels of the antioxidant genes SOD, CAT and GST, polyamine biosynthesis genes ADC1 and SAMDC, the late embryogenesis abundant protein-encoding gene ERD10D and drought-responsive genes NCED3, BG and RD26 were generally higher in GbMYB5-overexpressing tobacco than in the WT under drought stress. Collectively, our data suggested that GbMYB5 was positively involved in the plant adaptive response to drought stress.

Tomato yellow leaf curl virus (TYLCV) threatens tomato production worldwide by causing leaf yellowing, leaf curling, plant stunting and flower abscission. The current understanding of the host plant defense response to this virus is very limited. Using whole transcriptome sequencing, we analyzed the differential gene expression in response to TYLCV infection in the TYLCV-resistant tomato breeding line CLN2777A (R) and TYLCV-susceptible tomato breeding line TMXA48-4-0 (S). The mixed inoculated samples from 3, 5 and 7 day post inoculation (dpi) were compared to non-inoculated samples at 0 dpi. Of the total of 34831 mapped transcripts, 209 and 809 genes were differentially expressed in the R and S tomato line, respectively. The proportion of up-regulated differentially expressed genes (DEGs) in the R tomato line (58.37%) was higher than that in the S line (9.17%). Gene ontology (GO) analyses revealed that similar GO terms existed in both DEGs of R and S lines; however, some sets of defense related genes and their expression levels were not similar between the two tomato lines. Genes encoding for WRKY transcriptional factors, R genes, protein kinases and receptor (-like) kinases which were identified as down-regulated DEGs in the S line were up-regulated or not differentially expressed in the R line. The up-regulated DEGs in the R tomato line revealed the defense response of tomato to TYLCV infection was characterized by the induction and regulation of a series of genes involved in cell wall reorganization, transcriptional regulation, defense response, ubiquitination, metabolite synthesis and so on. The present study provides insights into various reactions underlining the successful establishment of resistance to TYLCV in the R tomato line, and helps in the identification of important defense-related genes in tomato for TYLCV disease management.