WRKY1-Mediated Interconversion of MeSA and SA in Neighbouring Apple Plants Enhances Defence Against Powdery Mildew.

Powdery mildew (PM), caused by the biotrophic fungus Podospharea leucotricha, is a major threat to apple production. Plant-plant communication (PPC) is a crucial strategy for plant communities to enhance their defence against pathogens. The interconversion of methyl salicylate (MeSA) and salicylic acid (SA) is critical for PPC regulation, but the mechanism of MeSA-mediated PPC is not fully understood. This study reveals a significant increase in SA and MeSA levels in neighbouring plants (receivers) following PM attack on emitter plants, activating defence responses in receivers. Notably, the expression of WRKY1, a previously characterized transcription factor, was upregulated in receivers, implicating its role in defence response modulation. WRKY1 was found to promote SA accumulation and enhance PM resistance in receivers. Importantly, WRKY1 positively regulates the expression of SABP2a, which catalysers MeSA to SA conversion, and negatively regulates SAMT1a, which functions in the reverse reaction. Consequently, WRKY1 facilitates the conversion of MeSA to SA in receivers, preventing its reversion and sustaining elevated SA levels. Collectively, our findings clarify the role of WRKY1 in enhancing the defence response to PM in receivers.