Department of Plant & Environmental Sciences, Weizmann Institute of Science, Rehovot, 76100, Israel.
Plant J. 2022 Feb;109(3):585-597. doi: 10.1111/tpj.15579. Epub 2021 Dec 2.
Disulfide-based regulation links the activity of numerous chloroplast proteins with photosynthesis-derived redox signals. The plastid terminal oxidase (PTOX) is a thylakoid-bound plastoquinol oxidase that has been implicated in multiple roles in the light and in the dark, which could require different levels of PTOX activity. Here we show that Arabidopsis PTOX contains a conserved C-terminus domain (CTD) with cysteines that evolved progressively following the colonization of the land by plants. Furthermore, the CTD contains a regulatory disulfide that is in the oxidized state in the dark and is rapidly reduced, within 5 min, in low light intensity (1-5 µE m sec ). The reduced PTOX form in the light was reoxidized within 15 min after transition to the dark. Mutation of the cysteines in the CTD prevented the formation of the oxidized form. This resulted in higher levels of reduced plastoquinone when measured at transition to the onset of low light. This is consistent with the reduced state of PTOX exhibiting diminished PTOX oxidase activity under conditions of limiting PQH substrate. Our findings suggest that AtPTOX-CTD evolved to provide light-dependent regulation of PTOX activity for the adaptation of plants to terrestrial conditions.
基于二硫键的调节将许多叶绿体蛋白的活性与光合作用衍生的氧化还原信号联系起来。质体末端氧化酶（PTOX）是一种定位于类囊体的质体醌氧化酶，它与光和暗中的多种作用有关，这可能需要不同水平的 PTOX 活性。在这里，我们表明拟南芥 PTOX 含有一个保守的 C 端结构域（CTD），其半胱氨酸在植物登陆后逐渐进化。此外，CTD 包含一个调节二硫键，该二硫键在黑暗中处于氧化状态，并在低光强（1-5μE m sec）下迅速还原，在 5 分钟内。在光下的还原型 PTOX 形式在过渡到黑暗后 15 分钟内重新氧化。CTD 中的半胱氨酸突变阻止了氧化形式的形成。这导致在过渡到低光时测量的还原型质体醌水平更高。这与 PTOX 还原态在 PQH 底物有限的条件下表现出降低的 PTOX 氧化酶活性的情况一致。我们的发现表明，AtPTOX-CTD 的进化提供了 PTOX 活性的光依赖性调节，以适应植物的陆地条件。
