Arabidopsis Golgi Anti-Apoptotic Proteins Confer Drought Tolerance to Water Deficiency by Enhancing Degradation of the Aquaporin PIP2;7

Water retention is one of the important factors for plants to survive under various stress conditions. In plants, the so-called plasma membrane intrinsic proteins (PIPs) are the main water channels that regulate the water status of plants. Membrane trafficking contributes to the functional regulation of major PIPs and is crucial for abiotic stress resilience. Arabidopsis Golgi anti-apoptotic proteins (GAAPs) play redundant function in resisting endoplasmic reticulum stress-induced cell death. However, much less is known about the connection between the cellular homeostasis response and the resistance to water deficiency. In this study, we analyzed the function of GAAPs under salt stress, osmotic stress and drought using single and multiple mutants of GAAP1 to GAAP4. GAAPs conferred salt resistance redundantly and GAAP4 played a major role in the resistance to water shortage. Aquaporin PIP2;7 (PIP3) was found interacting with GAAP1-4 by yeast two hybrid, cellular and co-immunoprecipitation assays. Genetic evidence suggests that PIP3 was essential for the function of GAAP4 against osmotic stress. GAAPs mutation(s) delayed the downregulation of PIP3 levels under osmotic stress. The internalization of PIP3 and plasma membrane was suppressed by GAAP4 mutation. So the positive function of GAAPs against water shortage stress might be partly due to its positive effect on membrane PIP3 cycling and turnover, thereby reducing cell water loss. The data also lay foundation for further studies on the connection of water retention regulation with cell fate decision.