Copper triggers plant immunity: Enhancing StRVE1 expression to activate salicylic acid accumulation by directly upregulating the StSID2-2 variant.

Phytophthora infestans significantly reduces the yield and quality of potato. Copper ion (Cu2+)-based antimicrobial compounds (CBACs) have been commercially applied for over a century to combat phytopathogens such as P. infestans. We had previously established that Cu2+ functions as an elicitor, triggering plant defense responses via the ethylene and salicylic acid (SA) signaling pathways. The current study found that treating potato plants with CBACs at dawn or dusk had varying effects on defense against late blight, suggesting that circadian rhythms affect the CBAC biocide efficacy. We further identified that Cu2+ upregulates the transcription of the circadian clock gene StRVE1 in potato plants. Overexpressing StRVE1 improved resistance against P. infestans, whereas silencing StRVE1 increased susceptibility to late blight, implying that StRVE1 plays a pivotal role in Cu2+-mediated immune response. StRVE1 binds directly to the promoter and stimulates transcription of the SA synthesis gene StSID2. In potato transcripts, StSID2 has two variants: StSID2-1 and StSID2-2. Overexpressing StSID2-1 or StSID2-2 showed contrasting effects on late blight resistance. StSID2-1 increased susceptibility, whereas StSID2-2 enhanced resistance. Furthermore, Cu2+ and StRVE1 promoted the transcription of StSID2-2, resulting in SA accumulation. SA improved potato resilience against late blight. Overall, we reveal a mechanism in which the StRVE1-StSID2-2 module, associated with SA synthesis, plays a role in Cu2+-mediated immune response in potato.