由激酶與磷酸酶交互作用成功地使可逆的蛋白質磷酸化反應調控著許多訊息傳遞機制。2C式蛋白質磷酸酶(PP2Cs)有形成逆境訊息傳遞的功能。六種Clade A PP2C被認為是離層酸 (ABA) 訊息傳遞的負調控者，而這些Clade A PP2C的活性是由PYL家族的離層酸接受器來調控。離層酸擁有使氣孔關閉以及讓基因表現的功能。然而剩下的三個「HAI」PP2C，Highly ABA-Induced1 (HAI1)，AKT1-Interacting PP2C1/HAI2 (AIP1) 和 HAI3仍待進一步了解。對於其它Clade PP2C如Clade E PP2C的功能我們也所知不多。我們發現HAI PP2C的突變株在低水勢會使脯氨酸和調節滲透壓溶質累積上升，而其它Clade A PP2C卻只有少量或沒有這些在乾旱下發生的特徵。hai1-2同時擁有增加鮮重並增加乾旱防衛基因，例如脫水素以及在胚胎發育後期豐富的蛋白質。單一突變的HAI PP2C無法感受離層酸，而雙重突變及三重突變則在發芽後保持對離層酸適當地高度感受性，並在發芽時無感受性。HAI PP2C與PYL家族有著受限的作用，即是HAI PP2C會特定與單體類型的PYL (PYL5 與 PYL7-10) 作用。而HAI1與PYL則有著特別弱且受限制的作用。HAI1與PYL作用的表現量在低水勢且HAI1高度表現的情況下下降也指出了受限的PYL的調控與HAI1的作用對於抗乾旱的表現型有著負調控的作用。這些數據整合起來指出了HAI PP2C，特別是HAI1在低水勢時對調節脯氨酸累積和滲透壓溶質累積的訊息傳遞有著顯著的削減。我同時找出了之前未被了解的Clade E PP2C的生理功能(這裡指E1， E2 和E3)。這些PP2C的突變株在低水勢時會使得脯氨酸累積上升，並同時也增加鮮重及根部延長。表現這些PP2C並非是由於外在供應的離層酸而是因低水勢而引導的。單一突變的PP2CE並不影響對離層酸的感受性，但e1-1e2-1的雙重突變使得種子在發芽與發芽後對離層酸的反應無感受性。這些數據指出PP2CE在低水勢逆境對生長上與其它表現型上扮演著負調控的作用，而不同於Clade A PP2C的機制。 Reversible protein phosphorylation regulates several signaling mechanisms and it is achieved by the combined activities of kinases and phosphatase. Type 2C protein phosphatases (PP2Cs) have emerging roles in stress signaling. Six of the Clade A PP2Cs are established as negative regulators of abscisic acid (ABA) signaling in which their activity is regulated by the PYL family of ABA receptors. However functions of the remaining three “HAI” PP2Cs, Highly ABA-Induced1 (HAI1), AKT1-Interacting PP2C1/HAI2 (AIP1) and HAI3, have remained unclear. We also have limiting knowledge about the function of other Clade PP2Cs, including Clade E PP2Cs. We found that mutants of HAI PP2Cs had increased proline and osmoregulatory solute accumulation at low ѱw, while other Clade A PP2Cs had no or lesser effect on these drought resistance traits. hai1-2 also had increased fresh weight and increased expression of drought protective genes such as dehydrins and late embryogenesis abundant proteins. HAI PP2C single mutants had no effect on ABA sensitivity, while double and triple mutants were moderately hypersensitive in post germination and insensitive in germination. HAI PP2Cs had limited interactions with the PYL family, in which they specifically interacted with monomer type of PYLs (PYL5 and PYL7-10). HAI1 had especially limited and also weak PYL interaction. Reduced expression of HAI1-interating PYLs at low ѱw when HAI1 expression was strongly induced also suggests the limited PYL regulation and HAI1 activity in negatively regulating the drought resistance phenotypes. The combined data indicate that the HAI PP2Cs, particularly HAI1, have a prominent role in attenuating the low ѱw signaling controlling proline and osmoregulatory solute accumulation. I also characterized the physiological functions of previously uncharacterized Clade E PP2Cs, (here referred to as E1, E2 and E3). Mutants of these PP2Cs also had elevated proline accumulation and in addition had, increased fresh weight and root elongation at low ѱw. Expression of these PP2Cs was induced by low ѱw but not by exogenously applied ABA. PP2CEs single mutants were unaffected in ABA sensitivity, while double mutant was ABA insensitive in seed germination and post germination ABA response. E1 and E2 were localized at cell periphery or plasma membrane. These data indicates that, PP2CEs play roles in negative regulation of growth and other phenotypes during low ѱw stress likely via mechanisms distinct from that of the Clade A PP2Cs.