Sly-miR1916 targets multiple target genes and negatively regulates the immune response in tomato.

MicroRNA1916 (miR1916) is one of the non-conserved miRNAs that respond to various stresses in plants, but little has been known at present about its mechanisms in biotic stresses. In this study, the expression of sly-miR1916 in tomato (Solanum lycopersicum) was found to be down-regulated after infection with Phytophthora infestans or Botrytis cinerea. Tomato plants that overexpressed sly-miR1916 displayed significant enhancement in susceptibility to P. infestans and B.cinerea infection, as well as increased tendency to produce reactive oxygen species (ROS). Silencing of sly-miR1916 by short tandem target mimic (STTM) and artificial microRNA (amiRNA) strategies caused the tomato plants to become more tolerant to adverse conditions. In addition, lower sly-miR1916 expression could up-regulate the expression of strictosidine synthase (STR-2), UDP-glycosyltransferases (UGTs), late blight resistance protein homolog R1B-16, disease resistance protein RPP13-like and MYB transcription factor (MYB12), which ultimately resulted in the accumulation of α-tomatine and anthocyanins via STR-2, UGTs and MYB12. Furthermore, ectopic expression of sly-miR1916/STR-2 significantly changed the tolerance of tobacco to B. cinerea. Taken together, the results demonstrated that sly-miR1916 might regulate the expression of STR-2, UGT and MYB12 in tomato plant, conferring sensitivity to biotic stress via modulating α-tomatine and anthocyanins.