The plant hormone abscisic acid (ABA) is fundamental for land plant adaptation to water‐limited conditions. Osmostress, such as drought, induces ABA accumulation in angiosperms, triggering physiological responses such as stomata closure. The core components of angiosperm ABA signalling are soluble ABA receptors, group A protein phosphatase type 2C and SNF1‐related protein kinase2 (SnRK2). ABA also has various functions in non‐angiosperms, however, suggesting that its role in adaptation to land may not have been angiosperm‐specific. Indeed, among land plants, the core ABA signalling components are evolutionarily conserved, implying their presence in a common ancestor. Results of ongoing functional genomics studies of ABA signalling components in bryophytes and algae have expanded our understanding of the evolutionary role of ABA signalling, with genome sequencing uncovering the ABA core module even in algae. In this review, we describe recent discoveries involving the ABA core module in non‐angiosperms, tracing the footprints of how ABA evolved as a phytohormone. We also cover the latest findings on Raf‐like kinases as upstream regulators of the core ABA module component SnRK2. Finally, we discuss the origin of ABA signalling from an evolutionary perspective.

中文翻译：

---

从进化的角度解码植物中的ABA和渗透压信号

植物激素脱落酸（ABA）是陆地植物适应缺水条件的基础。诸如干旱等渗透压会诱导被子植物中的ABA积累，从而触发诸如气孔关闭之类的生理反应。被子植物ABA信号传导的核心成分是可溶性ABA受体，A组2C型蛋白磷酸酶和SNF1相关蛋白激酶2（SnRK2）。ABA在非被子植物中也具有多种功能，但表明它在适应土地中的作用可能不是被子植物特有的。实际上，在陆地植物中，核心的ABA信号转导成分在进化上是保守的，这意味着它们存在于共同的祖先中。正在进行的对苔藓植物和藻类中ABA信号成分的功能基因组学研究的结果，扩大了我们对ABA信号的进化作用的认识，基因组测序甚至在藻类中也发现了ABA核心模块。在这篇综述中，我们描述了涉及非血管植物的ABA核心模块的最新发现，追踪了ABA如何作为植物激素进化的足迹。我们还将涵盖Raf样激酶作为核心ABA模块组件SnRK2的上游调节剂的最新发现。最后，我们从进化的角度讨论了ABA信号转导的起源。