Molecular Mechanism of miR160d in Regulating Kiwifruit Resistance to Botrytis cinerea

Gray mold caused by Botrytis cinerea leads to huge economic losses to the kiwifruit (Actinidia chinensis) industry. Elucidating the molecular mechanism responding to B. cinerea is the theoretical basis for the resistance to molecular breeding of kiwifruit. Previous studies have shown that miR160 regulates plant disease resistance through the indole-3-acetic acid (IAA) signaling pathway. In this study, kiwifruit "Hongyang" was used as the material, and Ac-miR160d and its target genes were identified and cloned. Overexpression and virus-induced gene silencing (VIGS) technology combined with RNA-seq were adopted to analyze the regulatory role of Ac-miR160d in kiwifruit resistance to B. cinerea. Silencing Ac-miR160d (AcMIR160d-KN) increased kiwifruit sensitivity to B. cinerea, whereas overexpression of Ac-miR160d (AcMIR160d-OE) increased kiwifruit resistance to B. cinerea, suggesting that Ac-miR160d positively regulates kiwifruit resistance to B. cinerea. In addition, overexpression of Ac-miR160d in kiwifruit increased antioxidant enzyme activities, such as catalase (CAT) and superoxide dismutase (SOD), and endogenous phytohormone IAA and salicylic acid (SA) content, in response to B. cinerea-induced stress. RNA-seq identified 480 and 858 unique differentially expressed genes in the AcMIR160d-KN vs CK and AcMIR160d-OE vs CK groups, respectively, with fold change ≥2 and false discovery rate <0.01. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis revealed that families associated with "biosynthesis of secondary metabolites" are possibly regulated by Ac-miR160d. "Phenylpropanoid biosynthesis", "flavonoid biosynthesis", and "terpenoid backbone biosynthesis" were further activated in the two comparison groups upon B. cinerea infection. Our results may reveal the molecular mechanism by which miR160d regulates kiwifruit resistance to B. cinerea and may provide gene resources for molecular breeding in kiwifruit resistance.