Poplar miR1447 Is a Negative Regulator of Disease Resistance Through the SA-Dependent Pathway

Although microRNA1447 (miR1447) regulates poplar responses to abiotic stress and pest infestation, how miR1447 regulates poplar immunity against pathogens and its underlying molecular mechanisms remain to be elucidated. Here, we revealed that miR1447 functioned as a negative regulator of poplar disease resistance against fungal and bacterial pathogens using overexpression (OE) and short tandem target mimic (STTM) poplar lines of miR1447. Moreover, we demonstrated that PopTCTP contributed to poplar immunity as a target of miR1447 through integrative analysis of overexpression and RNAi lines, degradomes, transient co-expression assay and GFP fluorescence report system, and found that PopTCTP interacted with dnaJ A6. Further molecular and genetic analyses revealed that the promoters of miR1447 and PopTCTP were responsive to exogenous salicylic acid (SA) treatment. We showed that the negative regulatory role of miR1447 in SA signalling and poplar resistance was weakened with exogenous SA treatment. Notably, the miR1447-PopTCTP module contributed to PTI in poplar triggered by flg22 and associated with crosstalk between PTI and ETI via regulating MAPK signalling and scavenging ROS. Taken together, these findings unveil a novel pathway by which the miR1447-PopTCTP-SA signalling mediates disease resistance to diverse pathogens in poplar, offering promising genetic targets for tree breeding of disease resistance.