Zhao, C.Wang, Y.Chan, K.X.Marchant, D.B.Franks, P.J.Randall, D.Tee, E.E.Chen, G.Ramesh, S.Phua, S.Y.Zhang, B.Hills, A.Dai, F.Xue, D.Gilliham, M.Tyerman, S.Nevo, E.Wu, F.Zhang, G.Wong, G.K.S.et al.2019-07-022019-07-022019Proceedings of the National Academy of Sciences of the United States of America, 2019; 116(11):5015-50200027-84241091-6490http://hdl.handle.net/2440/119851Chloroplast retrograde signaling networks are vital for chloroplast biogenesis, operation, and signaling, including excess light and drought stress signaling. To date, retrograde signaling has been considered in the context of land plant adaptation, but not regarding the origin and evolution of signaling cascades linking chloroplast function to stomatal regulation. We show that key elements of the chloroplast retrograde signaling process, the nucleotide phosphatase (SAL1) and 3'-phosphoadenosine-5'-phosphate (PAP) metabolism, evolved in streptophyte algae-the algal ancestors of land plants. We discover an early evolution of SAL1-PAP chloroplast retrograde signaling in stomatal regulation based on conserved gene and protein structure, function, and enzyme activity and transit peptides of SAL1s in species including flowering plants, the fern Ceratopteris richardii, and the moss Physcomitrella patens Moreover, we demonstrate that PAP regulates stomatal closure via secondary messengers and ion transport in guard cells of these diverse lineages. The origin of stomata facilitated gas exchange in the earliest land plants. Our findings suggest that the conquest of land by plants was enabled by rapid response to drought stress through the deployment of an ancestral SAL1-PAP signaling pathway, intersecting with the core abscisic acid signaling in stomatal guard cells.enCopyright © 2019 the Author(s). Published by PNAS. This open access article is distributed under Creative Commons Attribution-NonCommercial-NoDerivatives License 4.0 (CC BY-NC-ND).Comparative genomics; water stress; green plant evolution; signal transduction; stomataJournal article003010887510.1073/pnas.18120921160004609115000462-s2.0-85062821267460855Ramesh, S. [0000-0003-2230-4737]Gilliham, M. [0000-0003-0666-3078]Tyerman, S. [0000-0003-2455-1643]Chen, Z.H. [0000-0002-7531-320X]