Boudsocq Marie, Droillard Marie-Jo, Barbier-Brygoo Hélène, Laurière Christiane
Institut des Sciences du Végétal, UPR 2355, CNRS, 1 av. de la terrasse, 91198 Gif sur Yvette Cedex, France.
Plant Mol Biol. 2007 Mar;63(4):491-503. doi: 10.1007/s11103-006-9103-1.
In Arabidopsis cell suspension, hyperosmotic stresses (mannitol and NaCl) were previously shown to activate nine sucrose non-fermenting 1 related protein kinases 2 (SnRK2s) whereas only five of them were also activated by abscisic acid (ABA) treatment. Here, the possible activation by phosphorylation/ dephosphorylation of each kinase was investigated by studying their phosphorylation state after osmotic stress, using the Pro-Q Diamond, a specific dye for phosphoproteins. All the activated kinases were phosphorylated after osmotic stress but the induced phosphorylation changes were clearly different depending on the kinase. In addition, the increase of the global phosphorylation level induced by ABA application was lower, suggesting that different mechanisms may be involved in SnRK2 activation by hyperosmolarity and ABA. On the other hand, SnRK2 kinases remain activated by hyperosmotic stress in ABA-deficient and ABA-insensitive mutants, indicating that SnRK2 osmotic activation is independent of ABA. Moreover, using a mutant form of SnRK2s, a specific serine in the activation loop was shown to be phosphorylated after stress treatments and essential for activity and/or activation. Finally, SnRK2 activity was sensitive to staurosporine, whereas SnRK2 activation by hyperosmolarity or ABA was not, indicating that SnRK2 activation by phosphorylation is mediated by an upstream staurosporine-insensitive kinase, in both signalling pathways. All together, these results indicate that different phosphorylation mechanisms and at least three signalling pathways are involved in the activation of SnRK2 proteins in response to osmotic stress and ABA.
在拟南芥细胞悬浮液中，先前研究表明高渗胁迫（甘露醇和氯化钠）可激活9种蔗糖非发酵1相关蛋白激酶2（SnRK2s），而其中只有5种也可被脱落酸（ABA）处理激活。在此，通过使用一种针对磷酸化蛋白的特异性染料Pro-Q Diamond，研究渗透胁迫后各激酶的磷酸化状态，探讨了每种激酶通过磷酸化/去磷酸化实现激活的可能性。所有被激活的激酶在渗透胁迫后均发生了磷酸化，但诱导的磷酸化变化因激酶而异。此外，ABA处理诱导的整体磷酸化水平升高较低，这表明高渗和ABA激活SnRK2可能涉及不同机制。另一方面，在ABA缺陷型和ABA不敏感型突变体中，SnRK2激酶仍可被高渗胁迫激活，这表明SnRK2的渗透激活不依赖于ABA。此外，使用SnRK2s的突变形式，研究发现激活环中的一个特定丝氨酸在胁迫处理后会发生磷酸化，且对活性和/或激活至关重要。最后，SnRK2活性对星形孢菌素敏感，而高渗或ABA对SnRK2的激活则不敏感，这表明在这两种信号通路中，磷酸化介导的SnRK2激活是由一种上游对星形孢菌素不敏感的激酶介导的。综上所述，这些结果表明，不同的磷酸化机制以及至少三种信号通路参与了SnRK2蛋白响应渗透胁迫和ABA的激活过程。
