The MicroRNA156a-SPL module regulates kiwifruit resistance to Pseudomonas syringae pv. actinidiae.

MicroRNAs (miRNAs) are key regulators of plant growth, development, and immunity. However, their role in kiwifruit and other perennial fruit trees remains poorly characterized. Here, we demonstrate that Ac-miR156a functions as a negative regulator of kiwifruit resistance to Pseudomonas syringae pv. actinidiae (Psa). In the resistant cultivar "Jinkui," Ac-miR156a expression was significantly suppressed upon Psa infection, whereas it was markedly induced in the susceptible cultivar "Hongyang." Overexpression of miR156a increased kiwifruit susceptibility to Psa, while silencing miR156a via short-tandem target mimic (STTM) constructs enhanced resistance. We identified 14 SQUAMOSA-PROMOTER-BINDING PROTEIN-LIKE (SPL) transcription factors as direct targets of Ac-miR156a, among which AcSPL6c and AcSPL14c were rapidly upregulated in the resistant cultivar and shown to positively regulate immunity against Psa. Furthermore, we revealed that the Ac-miR156a-SPL module regulates kiwifruit immunity by reprogramming the hormonal levels between salicylic acid (SA) and jasmonic acid (JA) signaling pathways, favoring SA-dominated defense against the biotrophic pathogen Psa. Collectively, our study elucidates a complete Ac-miR156a-AcSPL6c/14c regulatory pathway that fine-tunes kiwifruit immune outcomes through hormonal redistribution, providing both mechanistic insights and potential genetic targets for improving disease resistance in kiwifruit breeding programs.