Hydrogen peroxide sensor HPCA1 is an LRR receptor kinase in Arabidopsis

Hydrogen peroxide (H 2 O 2 ) is a major reactive oxygen species in unicellular and multicellular organisms, and is produced extracellularly in response to external stresses and internal cues 1 – 4 . H 2 O 2 enters cells through aquaporin membrane proteins and covalently modifies cytoplasmic proteins to regulate signalling and cellular processes. However, whether sensors for H 2 O 2 also exist on the cell surface remains unknown. In plant cells, H 2 O 2 triggers an influx of Ca 2+ ions, which is thought to be involved in H 2 O 2 sensing and signalling. Here, by using forward genetic screens based on Ca 2+ imaging, we isolated hydrogen-peroxide-induced Ca 2+ increases ( hpca ) mutants in Arabidopsis , and identified HPCA1 as a leucine-rich-repeat receptor kinase belonging to a previously uncharacterized subfamily that features two extra pairs of cysteine residues in the extracellular domain. HPCA1 is localized to the plasma membrane and is activated by H 2 O 2 via covalent modification of extracellular cysteine residues, which leads to autophosphorylation of HPCA1. HPCA1 mediates H 2 O 2 -induced activation of Ca 2+ channels in guard cells and is required for stomatal closure. Our findings help to identify how the perception of extracellular H 2 O 2 is integrated with responses to various external stresses and internal cues in plants, and have implications for the design of crops with enhanced fitness.