Aquaporins facilitate hydrogen peroxide entry into guard cells to mediate ABA- and pathogen-triggered stomatal closure ($)

Guard cells are crucial gatekeepers that control entry and exit of gases, water vapor, and pathogens. Rapid stomatal pore closure in response to pathogen perception or the hormone abscisic acid (ABA) is supported by activation of the aquaporin (water channel) PIP2;1. Rodrigues et al. investigated the contribution of PIP2;1 in guard cell responses to the pathogen-associated molecular pattern flg22, and the role of the reactive oxygen signal hydrogen peroxide (H₂O₂) in this response. Using plants expressing HyPer (an engineered fluorescent H₂O₂ sensor protein) they showed that pip2;1 mutant guard cells are limited in the entry of exogenous H₂O₂ in response to ABA or flg22, raising the possibility that PIP2;1 modulates guard cell turgor through both influx of signaling H₂O₂ as well as efflux of water. Proc. Natl. Acad. Sci. USA 10.1073/pnas.1704754114