A RAF-SnRK2-PP2C functional module regulates cell survival in the chlorophyte Chlamydomonas reinhardtii.

内容摘要

The SNF1-related protein kinase 2 (SnRK2) pathway is a central regulator of abiotic stress signaling in land plants, yet its evolutionary origins and functional conservation across the green lineage remain poorly understood. To determine whether this signaling module predates the streptophyte-chlorophyte divergence, we investigated the chlorophyte alga Chlamydomonas reinhardtii, which diverged from the streptophyte lineage over 1 billion years ago. Using a combination of reverse genetics and protein-protein interaction assays, we identified and characterized a bona fide SnRK2 signaling module in C. reinhardtii. We demonstrate that the isoform SnRK2.7 is essential for osmotic stress tolerance and general cellular viability. SnRK2.7 localizes to the contractile vacuole, an osmoregulatory organelle lost during streptophyte evolution, revealing a lineage-specific functional adaptation. Together with MAPKKK3, a B1/B3-RAF kinase, and the clade A protein phosphatase PP2C3, these components constitute a MAPKKK3-SnRK2.7-PP2C3 regulatory module in C. reinhardtii. Our findings demonstrate the presence of a functional SnRK2 pathway in a chlorophyte alga, suggesting that core components were established early in the green lineage. This work provides a foundation for comparative studies across green plants and underscores the need for broader taxonomic sampling to reconstruct the ancestral signaling networks underlying stress adaptation. SNF1相关蛋白激酶2(SnRK2)信号通路是陆地植物非生物胁迫信号转导的核心调控网络，但其在绿色植物谱系中的进化起源及功能保守性尚不清楚。为探究该信号模块是否早于链形植物与绿藻的分化事件而存在，本研究以莱茵衣藻(Chlamydomonas reinhardtii)为研究对象，该物种于约十亿年前从链形植物谱系分化而来。 通过反向遗传学与蛋白质互作分析，我们在莱茵衣藻中鉴定并表征了一个功能性的SnRK2信号模块。 结果表明，该激酶家族成员SnRK2.7对渗透胁迫耐受性及细胞长期存活至关重要；SnRK2.7蛋白定位于伸缩泡——一种在链形植物进化中丢失的渗透调节细胞器，提示该蛋白在绿色植物谱系演化中获得了特异性功能适应。进一步研究发现，SnRK2.7与MAPKKK3(一种B1/B3类RAF蛋白激酶)及A亚类PP2C蛋白磷酸酶PP2C3共同组成莱茵衣藻中的MAPKKK3‐SnRK2.7‐PP2C3调控模块。 本研究首次证明绿藻中存在功能性的SnRK2通路，表明该通路的核心组分在绿色植物早期进化中即已建立。该工作为理解植物非生物胁迫信号通路的进化起源提供了关键证据，同时强调了扩大系统发育类群研究对重建祖先胁迫适应网络不可或缺的重要性。.