Background: The two-component signaling (TCS) system is an important signal transduction machinery in prokaryotes and eukaryotes, excluding animals, that uses a protein phosphorylation mechanism for signal transmission.

Conclusion: Prokaryotes have a primitive type of TCS machinery, which mainly comprises a membrane- bound sensory histidine kinase (HK) and its cognate cytoplasmic response regulator (RR). Hence, it is sometimes referred to as two-step phosphorelay (TSP). Eukaryotes have more sophisticated signaling machinery, with an extra component - a histidine-containing phosphotransfer (HPT) protein that shuttles between HK and RR to communicate signal baggage. As a result, the TSP has evolved from a two-step phosphorelay (His–Asp) in simple prokaryotes to a multi-step phosphorelay (MSP) cascade (His–Asp–His–Asp) in complex eukaryotic organisms, such as plants, to mediate the signaling network. This molecular evolution is also reflected in the form of considerable structural modifications in the domain architecture of the individual components of the TCS system. In this review, we present TCS system's evolutionary journey from the primitive TSP to advanced MSP type across the genera. This information will be highly useful in designing the future strategies of crop improvement based on the individual members of the TCS machinery.

背景：二元信号传导（TCS）系统是原核生物和真核生物（不包括动物）中重要的信号转导机制，利用蛋白质磷酸化机制进行信号传递。

结论：原核生物具有原始类型的TCS机制，主要包括膜结合感觉组氨酸激酶（HK）及其同源细胞质反应调节剂（RR）。因此，它有时被称为两步磷光继电器 (TSP)。真核生物拥有更复杂的信号机制，带有一个额外的成分——一种含组氨酸的磷酸转移 (HPT) 蛋白，它在 HK 和 RR 之间穿梭来传递信号包。因此，TSP 已从简单原核生物中的两步磷酸中继 (His-Asp) 进化为复杂真核生物（例如植物、调解信号网络。这种分子进化还体现在 TCS 系统各个组件的域架构中的大量结构修改的形式。在这篇综述中，我们介绍了 TCS 系统从原始 TSP 到高级 MSP 类型的跨属演化历程。这些信息对于根据 TCS 机械的各个成员设计未来的作物改良策略非常有用。