Functional identification of sly-miR1919c in tomato resistance to Phytophthora infestans

MicroRNAs (miRNAs) play crucial regulatory roles in plant defense against pathogens. Our previous work identified sly-miR1919c as a potential participant in tomato resistance to late blight. In this study, qRT-PCR analysis revealed that the expression of mature sly-miR1919c was significantly suppressed in tomato leaves following inoculation with Phytophthora infestans or treatment with salicylic acid, whereas jasmonic acid treatment markedly induced its expression. Bioinformatic analysis showed that the miR1919 family has a limited phylogenetic distribution, being present in only three plant species, with high sequence conservation among mature members. Solyc08g067580 (UNP) was confirmed as the target gene of sly-miR1919c through 5′ RLM-RACE validation. qRT-PCR confirmed that UNP expression was upregulated in P. infestans-infected tomato leaves. The transgenic lines overexpressing sly-miR1919c (OE-miR1919c) exhibited increased susceptibility to late blight, which was associated with reduced UNP expression. Furthermore, silencing UNP via dsRNA-based SIGS demonstrated its function as a positive regulator of tomato resistance to late blight. Moreover, OE-miR1919c plants developed more severe disease symptoms characterized by enlarged necrotic lesions, increased cell death, and elevated accumulation of reactive oxygen species (ROS). These plants also exhibited leaf chlorosis and increased lateral branching. The osmotin-like protein (OLP) was identified as the UNP-interacting protein through yeast two-hybrid screening(Y2H) and Luciferase complementation imaging (LCI) assays. RNA-seq analysis revealed that overexpression of sly-miR1919c significantly altered the expression of genes associated with hormone signal transduction, MAPK signaling pathways, phenylpropanoid biosynthesis, and photosynthesis. During P. infestans infection, genes involved in hormone signal transduction and photosynthesis pathways were significantly downregulated in OE-miR1919c plants, and these genes were predominantly enriched in the GO term “response to stimulus”. Taken together, this study provides novel insights into the molecular mechanism underlying sly-miR1919c-mediated tomato resistance and highlights its potential as a genetic resource for tomato disease-resistant breeding.