Plant Physiology, Freie Universität Berlin, Dahlem Centre of Plant Sciences, Berlin 14195,Germany.
Plant Physiol. 2022 Oct 27;190(3):1997-2016. doi: 10.1093/plphys/kiac355.
Exposure of Arabidopsis (Arabidopsis thaliana) to 4°C imprints a cold memory that modulates gene expression in response to a second (triggering) stress stimulus applied several days later. Comparison of plastid transcriptomes of cold-primed and control plants directly before they were exposed to the triggering stimulus showed downregulation of several subunits of chloroplast NADPH dehydrogenase (NDH) and regulatory subunits of ATP synthase. NDH is, like proton gradient 5 (PGR5)-PGR5-like1 (PGRL1), a thylakoid-embedded, ferredoxin-dependent plastoquinone reductase that protects photosystem I and stabilizes ATP synthesis by cyclic electron transport (CET). Like PGRL1A and PGRL1B transcript levels, ndhA and ndhD transcript levels decreased during the 24-h long priming cold treatment. PGRL1 transcript levels were quickly reset in the postcold phase, but expression of ndhA remained low. The transcript abundances of other ndh genes decreased within the next days. Comparison of thylakoid-bound ascorbate peroxidase (tAPX)-free and transiently tAPX-overexpressing or tAPX-downregulating Arabidopsis lines demonstrated that ndh expression is suppressed by postcold induction of tAPX. Four days after cold priming, when tAPX protein accumulation was maximal, NDH activity was almost fully lost. Lack of the NdhH-folding chaperonin Crr27 (Cpn60β4), but not lack of the NDH activity modulating subunits NdhM, NdhO, or photosynthetic NDH subcomplex B2 (PnsB2), strengthened priming regulation of zinc finger of A. thaliana 10, which is a nuclear-localized target gene of the tAPX-dependent cold-priming pathway. We conclude that cold-priming modifies chloroplast-to-nucleus stress signaling by tAPX-mediated suppression of NDH-dependent CET and that plastid-encoded NdhH, which controls subcomplex A assembly, is of special importance for memory stabilization.
拟南芥（Arabidopsis thaliana）暴露于 4°C 会产生冷记忆，从而调节几天后应对第二次（触发）胁迫刺激的基因表达。在冷预处理的拟南芥植物和对照植物直接暴露于触发刺激之前，比较质体转录组，发现叶绿体 NADPH 脱氢酶（NDH）的几个亚基和 ATP 合酶的调节亚基下调。NDH 像质子梯度 5（PGR5）-PGR5 样 1（PGRL1）一样，是一种定位于类囊体、依赖铁氧还蛋白的质醌还原酶，可保护光系统 I 并通过循环电子传递（CET）稳定 ATP 合成。与 PGRL1A 和 PGRL1B 转录本水平一样，ndhA 和 ndhD 转录本水平在 24 小时长的冷预处理期间降低。PGRL1 转录本水平在冷后相快速重置，但 ndhA 表达仍然较低。在接下来的几天内，其他 ndh 基因的转录本丰度降低。比较质体结合抗坏血酸过氧化物酶（tAPX）-无和瞬时 tAPX 过表达或 tAPX 下调的拟南芥系表明，ndh 表达受冷后诱导的 tAPX 抑制。冷预处理 4 天后，当 tAPX 蛋白积累达到最大值时，NDH 活性几乎完全丧失。缺乏 NdhH 折叠伴侣蛋白 Crr27（Cpn60β4），而不是缺乏 NDH 活性调节亚基 NdhM、NdhO 或光合 NDH 亚基 B2（PnsB2），增强了锌指蛋白 A.thaliana 10 的冷预处理调节，锌指蛋白 A.thaliana 10 是 tAPX 依赖的冷预处理途径的核定位靶基因。我们得出结论，冷预处理通过 tAPX 介导的 NDH 依赖性 CET 抑制来修饰叶绿体到细胞核的应激信号，并且对亚基 A 组装起控制作用的质体编码 NdhH 对记忆稳定特别重要。
