MPK3 as a Signalling Hub in Plants: Integrating Plant Growth, Development and Stress Response.

The mitogen-activated protein kinase (MAPK) cascade constitutes a core component of signal transduction pathways in eukaryotic organisms. With its precise, efficient, and specific mechanism of action, this cascade pathway integrates, amplifies, and rapidly transmits signals. Among them, the specificity and functional diversity of the MPK3 cascade depend on the phosphorylation interaction between MKK and MPK3, as well as the specific interaction between MPK3 and its substrates. MPK3 targets an extremely diverse array of substrates, including transcription factors, RNA-binding proteins, enzymes, and transporters. The summary of the regulatory role of the MPK3 signal mainly focuses on three functional mechanisms: The most well-known regulatory mechanism is to recognize and phosphorylate substrate proteins or transcription factors, thereby affecting the stability and transcriptional activity of downstream substrates, and thus regulating the transcriptional regulatory activity and expression of downstream genes. MPK3 can also participate in downstream functional regulation by triggering the MAPKKK-MKK4/5-MPK3/6 signaling pathways or feedback mechanisms. MPK3 can exert regulatory effects independently or together with MPK6. The redundancy of the MPK3/6 function is related to the synergistic effect of the component cascade reaction, as well as the dose-dependent activation effect. This article presents a comprehensive synthesis of the latest research progress on the regulatory role of MPK3, in plant growth, development, and stress adaptation and defence. Moreover, it provides critical evaluations and forward-looking perspectives on the future investigation of the underlying molecular mechanisms governing MPK3-mediated regulation.