Isolation of Arabidopsis extracellular ATP‐binding proteins by affinity proteomics and identification of PHOSPHOLIPASE C‐LIKE 1 as an extracellular protein essential for fumonisin B1 toxicity

Abstract

ATP is secreted to the extracellular matrix where it activates plasma membrane receptors for controlling plant growth and stress‐adaptive processes. DOES NOT RESPOND TO NUCLEOTIDES 1 (DORN1), the first plant ATP receptor was identified, but key downstream proteins are sought after. Here, we identified 120 proteins secreted by Arabidopsis cell cultures and screened them for putative stress‐responsive proteins using ATP‐affinity purification. We report three Arabidopsis proteins isolated by ATP‐affinity: PEROXIDASE 52, SUBTILASE‐LIKE SERINE PROTEASE 1.7, and PHOSPHOLIPASE C‐LIKE 1. In wildtype Arabidopsis, expression of genes encoding all three proteins responded to fumonisin B1, a cell death‐activating mycotoxin. Expression of PEROXIDASE 52 and PHOSPHOLIPASE C‐LIKE 1 genes was altered in fumonisin B1‐resistant salicylic acid induction‐deficient (sid2) mutants. Exposure to fumonisin B1 suppressed PHOSPHOLIPASE C‐LIKE 1 expression in sid2 mutants, suggesting that inactivation of this gene might provide mycotoxin tolerance. Accordingly, gene knockout mutants of PHOSPHOLIPASE C‐LIKE 1 were resistant to fumonisin B1‐induced death. Activation of PHOSPHOLIPASE C‐LIKE 1 gene expression by exogenous ATP was not blocked in dorn1 loss‐of‐function mutants, indicating that DORN1 is not required. Furthermore, exogenous ATP rescued both wildtype and dorn1 mutants from fumonisin B1 toxicity, suggesting that different ATP receptor(s) are operational in this process. Our results point to the existence of additional plant ATP receptor(s) and provide crucial downstream targets for use in designing screens to identify these receptors. Finally, PHOSPHOLIPASE C‐LIKE 1 serves as a convergence point for fumonisin B1 and extracellular ATP signalling, and functions in Arabidopsis stress response to fumonisin B1.