SOS1 safeguards plant circadian rhythm against daily salt fluctuations.
SOS1 safeguards plant circadian rhythm against daily salt fluctuations.
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DOI：
10.1073/pnas.2212950119
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发表时间：
2022-09-06
影响因子：
11.1
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中科院分区：
文献类型：
--
作者：
地球的自转造成了环境因素的周期性变化。为了充分利用这些可预测的振荡因素以获得更好的适应性，植物进化出了一种复杂的内源性计时系统，称为昼夜节律钟。植物生物钟系统通过其输入途径感知环境线索，如光线和温度。然后，输入通路将这些环境线索传递到核心振荡器，核心振荡器由互锁的转录-翻译反馈回路组成，通过输出通路在各种生理过程中产生自我维持的昼夜节律（1，2）。由于大多数核心振荡器都是转录因子，因此植物生物钟对整体转录有着深远的影响。全面的转录组学研究表明，在特定条件下，拟南芥周期中89%的转录物和生物钟系统负责拟南芥中超过三分之一的基因的振荡表达（3）。引人注目的是，一项关于植物转录组变化对盐、渗透和冷胁迫的响应的研究表明，68%的昼夜节律振荡基因参与了胁迫反应（4）。现在越来越清楚的是，植物生物钟在不同的植物胁迫反应中起着不可或缺的作用（5）。在PNAS中，Cha等人发现盐过度敏感1（SOS 1），质膜（PM）Na+/H+反向转运蛋白，与核心生物钟组分GIGANTEA（GI）相互作用并稳定，以实现植物生物钟在每日波动的盐水平下的周期补偿（6）。由于不适当的灌溉方法，滥用肥料和工业污染，盐胁迫已成为限制各种作物产量的主要障碍之一，影响了世界总土地面积的6%以上（7）。在响应由盐胁迫引发的离子毒性时，植物依靠SOS途径将过量的Na+从细胞质运输到质外体，从而确保内源离子稳态。虽然Na+的真正传感器尚未在植物中被确定，但发现细胞内和细胞间Na+水平升高会触发胞质Ca 2+信号，该信号由SOS 3（EF-手Ca 2+结合蛋白）解码。SOS 3以Ca 2+依赖性方式与丝氨酸/苏氨酸蛋白激酶SOS 2相互作用并激活SOS 2。活化的SOS 2然后磷酸化SOS 1，其释放由SOS 1的C-末端自抑制结构域的抑制，活化SOS 1的Na+/H+反向转运蛋白活性。SOS 1将过量的Na+转运出细胞质，以换取H+的向内转运。通过盐胁迫激活的PM H+-ATP酶产生跨PM的H+梯度，其驱动SOS 1的活性（8）。
The rotation of the Earth has generated cyclic changes in environmental factors. To fully exploit these predictable oscillatory factors for better fitness, plants have evolved an intricate endogenous timing system called the circadian clock. The plant circadian clock system perceives environmental cues like light and temperature through its input pathways. The input pathways then deliver these environmental cues to the core oscillators which are composed of interlocked transcription–translation feedback loops, generating self-sustaining circadian rhythms in various physiological processes through the output pathways (1, 2). Since most of the core oscillators are transcription factors, the plant circadian clock influences global transcription profoundly. Comprehensive transcriptomic studies suggest that 89% of transcripts in Arabidopsis cycle under certain conditions and the circadian clock system is responsible for the oscillatory expression of more than one-third of the genes in Arabidopsis (3). Strikingly, a study on plant transcriptome changes in response to salt, osmotic, and cold stresses suggests that 68% of the circadian oscillatory genes are involved in stress responses (4). It is now increasingly clear that the plant circadian clock plays an indispensable role in diverse plant stress responses (5). In PNAS, Cha et al. discover that SALT OVERLY SENSITIVE 1 (SOS1), a plasma membrane (PM) Na+/H+ antiporter, interacts with and stabilizes GIGANTEA (GI), a core circadian clock component, to realize period compensation of plant circadian clock under daily fluctuating salt levels (6). Due to inappropriate irrigation practices, misuse of fertilizer, and industrial pollution, salt stress has become one of the major hurdles curbing the yield of various crops, affecting over 6% of the world’s total land area (7). In response to the ionic toxicity triggered by salt stress, plants rely on the SOS pathway to transport excessive Na+ from the cytoplasm to the apoplast, thus ensuring endogenous ionic homeostasis. Although the bona fide sensor of Na+ is yet to be identified in plants, elevated intracellular and intercellular Na+ levels were found to trigger cytosolic Ca2+ signals, which are decoded by SOS3, an EF-hand Ca2+-binding protein. SOS3 interacts with and activates SOS2, a serine/threonine protein kinase, in a Ca2+-dependent manner. Activated SOS2 then phosphorylates SOS1, which releases the inhibition by the C-terminal autoinhibitory domain of SOS1, activating the Na+/H+ antiporter activity of SOS1. SOS1 transports excessive Na+ outward of the cytoplasm in exchange for inward transportation of H+. The H+ gradient across the PM which drives the activity of SOS1 is generated by PM H+-ATPase activated by salt stress (8).
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