Unique Drought Resistance Functions of the Highly ABA-Induced Clade A Protein Phosphatase 2Cs

摘要

Six Arabidopsis (Arabidopsis thaliana) clade A protein phosphatase 2Cs (PP2Cs) have established abscisic acid (ABA) signalingroles; however, phenotypic roles of the remaining three “HAI” PP2Cs, Highly ABA-Induced1 (HAI1), AKT1-Interacting PP2C1/HAI2, and HAI3, have remained unclear. HAI PP2C mutants had enhanced proline and osmoregulatory solute accumulation atlow water potential, while mutants of other clade A PP2Cs had no or lesser effect on these drought resistance traits. hai1-2 alsohad increased expression of abiotic stress-associated genes, including dehydrins and late embryogenesis abundant proteins, butdecreased expression of several defense-related genes. Conversely, the HAI PP2Cs had relatively less impact on several ABAsensitivity phenotypes. HAI PP2C single mutants were unaffected in ABA sensitivity, while double and triple mutants weremoderately hypersensitive in postgermination ABA response but ABA insensitive in germination. The HAI PP2Cs interactedmost strongly with PYL5 and PYL7 to -10 of the PYL/RCAR ABA receptor family, with PYL7 to -10 interactions being relativelylittle affected by ABA in yeast two-hybrid assays. HAI1 had especially limited PYL interaction. Reduced expression of the mainHAI1-interacting PYLs at low water potential when HAI1 expression was strongly induced also suggests limited PYL regulationand a role of HAI1 activity in negatively regulating specific drought resistance phenotypes. Overall, the HAI PP2Cs had greatesteffect on ABA-independent low water potential phenotypes and lesser effect on classical ABA sensitivity phenotypes. Both thisand their distinct PYL interaction demonstrate a new level of functional differentiation among the clade A PP2Cs and a point ofcross talk between ABA-dependent and ABA-independent drought-associated signaling.