Involvement of miRNAs-mediated senescence and salicylic acid defense in postharvest litchi downy blight

Litchi downy blight, caused by Peronophythora litchii, results in decline of market value of litchi fruit. In this study, roles of microRNAs (miRNAs) in regulating litchi fruit response to P. litchii infection was investigated. Results showed that P. litchii infection decreased anthocyanin content while accelerating fruit senescence. Salicylic acid (SA) content was also altered by P. litchii infection. Meanwhile, expression levels of LcmiR159, LcmiR828, LcmiR160 and LcmiR167 were investigated using stem-loop real-time quantitative PCR (RT-qPCR). Then, we identified LcGAMYB, LcTT2, LcARF18 and LcARF8 as their target genes, respectively, based on RNA Ligase-Mediated (RLM)-5 '-RACE, transient co-expression assay in Nicotiana benthamiana as well as expression change of target genes. Our results suggested that LcmiR159-LcGAMYB and LcmiR828-LcTT2 modules participated in litchi downy blight possibly through regulating fruit senescence while LcmiR160-LcARF18 and LcmiR167-LcARF8 through SA-mediated defense response. This study provides new knowledge on deployment of miRNAs to increase litchi fruit resistance against fungal disease.