Extracellular ATP targets Arabidopsis RIBONUCLEASE 1 to suppress mycotoxin stress‐induced cell death

Extracellular ATP is a purinergic signal with important functions in regulating plant growth and stress‐adaptive responses, including programmed cell death. While signalling events proximate to receptor activation at the plasma membrane have been characterised, downstream protein targets and the mechanism of cell death activation/regulation are unknown. We designed a proteomic screen to identify ATP‐responsive proteins in Arabidopsis cell cultures exposed to mycotoxin stress via fumonisin B1 (FB1) application. Arabidopsis RIBONUCLEASE 1 (RNS1) was identified by the screen, and transgenic plants overexpressing native RNS1 showed greater susceptibility to FB1, while a gene knockout rns1 mutant and antisense RNS1 transgenic plants were resistant to FB1‐induced cell death. Native RNS1 complemented rns1 mutants and restored the cell death response to FB1, while a catalytically inactive version of the ribonuclease could not. The FB1 resistance of salicylic acid (SA)‐depleted nahG‐expressing plants was abolished by transformation with native RNS1, but not the catalytically dead version. The mechanism of FB1‐induced cell death is activation of RNS1‐dependent RNA cleavage, which is blocked by ATP via RNS1 suppression, or enhanced by SA through induction of RNS1 expression. Our study reveals RNS1 as a previously unknown convergence point of ATP and SA signalling in the regulation of stress‐induced cell death.