Exogenous methyl jasmonate promotes susceptibility of strawberry crown rot caused by Colletotrichum siamense through down-regulating defense gene and flavonoids biosynthesis

Colletotrichum siamense, a hemibiotrophic pathogen which caused serious strawberry crown rot. Jasmonic acid (JA) is shown to reduce or promote pathogen infection, but the effect of JA on strawberry crown rot is still unknown. Identified the effect and mechanism of JA on strawberry crown rot is the base of resistance induction and genetic improvement for strawberry crown rot. Exogenous methyl jasmonate (MeJA) was tested for its effect for C. siamense causing strawberry crown rot in this study. MeJA significantly increased lesion width and hypha density caused by C. siamense infection in crown. MeJA reprogrammed crown transcriptome, and it induced 1642 significantly differentially expressed genes. In addition, most differentially expressed genes were most enriched in ‘metabolite biosynthetic processes’ and ‘response to stimulus’ by COG enrichment and KOG function classification. Further, KEGG function enrichment showed ‘flavonoid biosynthesis’ vested in ‘metabolite biosynthetic processes’, ‘plant-pathogen interaction’ vested in ‘response to stimulus’ were suppressed by MeJA. qRT-PCR showed expressions of defense genes like heat shock protein, MYB and cellulose synthase A catalytic subunit 8 and structural genes in ‘flavonoid biosynthesis’ were all suppressed. Confirmed with gene expressions, MeJA decreased total flavonoid and down-regulated activities of chalcone synthase and chalcone isomerase. Thus, exogenous MeJA enhanced C. siamense causing crown rot in strawberry by down-regulating defense genes and flavonoids biosynthesis.