EGR2 phosphatase regulates OST1 kinase activity and freezing tolerance in Arabidopsis

First author: Yanglin Ding; Affiliations: China Agricultural University (中國農業大學): Beijing, China

Corresponding author: Shuhua Yang

OST1 (open stomata 1) protein kinase (激酶) plays a central role in regulating freezing tolerance in Arabidopsis; however, the mechanism underlying cold activation of OST1 remains unknown. Here, we report that a plasma membrane‐localized clade‐E growth‐ egulating 2 (EGR2) phosphatase (磷酸酶) interacts with OST1 and inhibits OST1 activity under normal conditions. EGR2 is N‐myristoylated byN‐myristoyltransferase (N-肉豆蔻酰基轉移酶) NMT1 at 22°C, which is important for its interaction with OST1. Moreover, myristoylation of EGR2 is required for its function in plant freezing tolerance. Under cold stress, the interaction of EGR2 and NMT1 is attenuated (減弱), leading to the suppression of EGR2 myristoylation in plants. Plant newly synthesized unmyristoylated EGR2 has decreased binding ability to OST1 and also interferes with the EGR2‐OST1 interaction under cold stress. Consequently, the EGR2‐mediated inhibition of OST1 activity is released. Consistently, mutations of EGRs cause plant tolerance to freezing, whereas overexpression of EGR2 exhibits decreased freezing tolerance. This study thus unravels a molecular mechanism underlying cold activation of OST1 by membrane‐localized EGR2 and suggests that a myristoyl (肉豆蔻酰) switch on EGR2 helps plants to adapt to cold stress.

OST1蛋白激酶在調控擬南芥的耐凍性方面扮演重要的作用，然而OST1的低溫激活機制還不清楚。本文中，作者報道了一個定位于質膜的EGR2磷酸酶與OST1相互作用，在正常條件下抑制OST1的活性。N-肉豆蔻酰基轉移NMT1能夠在22°C條件下肉豆蔻酰基化EGR2，這對于NMT1與OST1的互作是非常重要的。此外，EGR2的肉豆蔻酰基化對于植株的耐凍性是必需的。在冷脅迫下，NMT1與EGR2的互作減弱，導致了植株中EGR2肉豆蔻酰基化的抑制。植株中新合成的未肉豆蔻酰基化的EGR2與OST1結合的能力也有所降低，同時在冷脅迫下干擾EGR2‐OST1的互作。因此，EGR2介導的OST1活性抑制得到緩解。另外，EGRs的突變增強了植株對凍害的抗性，而過表達EGR2基因降低植株對于凍害的抗性。本文的研究揭示了OST1低溫激活的底層分子機制，主要由定位于膜上的EGR2蛋白介導的肉豆蔻酰化控制，進而提升植株對于低溫脅迫的適應。