Phosphoproteome Dynamics Upon Changes in Plant Water Status Reveal Early Events Associated With Rapid Growth Adjustment in

Plant growth adjustment during water deficit is a crucial adaptive response. The rapid fine-tuned control achieved at the post-translational level is believed to be of consid-erable importance for regulating early changes in plant growth reprogramming. Aiming at a better understanding of early responses to contrasting plant water statuses, we carried out a survey of the protein phosphorylation events in the growing zone of maize leaves upon a range of water regimes. In this study, the impact of mild and severe water deficits were evaluated in comparison with constant op-timal watering and with recovery periods lasting 5, 10, 20, 30, 45, and 60 min. Using four biological replicates per treatment and a robust quantitative phosphoproteomic methodology based on stable-isotope labeling, we iden-tified 3664 unique phosphorylation sites on 2496 proteins. The abundance of nearly 1250 phosphorylated peptides was reproducibly quantified and profiled with high confi-dence among treatments. A total of 138 phosphopeptides displayed highly significant changes according to water regimes and enabled to identify specific patterns of re-sponse to changing plant water statuses. Further quanti-fication of protein amounts emphasized that most phos-phorylation changes did not reflect protein abundance variation. During water deficit and recovery, extensive changes in phosphorylation status occurred in critical regulators directly or indirectly involved in plant growth and development. These included proteins influencing epigenetic control, gene expression, cell cycle-dependent processes and phytohormone-mediated responses. Some of the changes depended on stress intensity whereas oth-ers depended on rehydration duration, including rapid re-coveries that occurred as early as 5 or 10 mins after rewa-tering. By combining a physiological approach and a quantitative phosphoproteomic analysis, this work provides new insights into the in vivo early phosphorylation events triggered by rapid changes in plant water status, and their possible involvement in plant growth-related proces