Two mitogen-activated protein kinase (MAPK) cascades with MPK4 and MPK3/MPK6 as the bottommost kinases are key to plant growth/development and immune signaling. Disruption of the MPK4 cascade leads to severe dwarfism and autoimmunity, complicating the study of MPK4 in plant growth/development and immunity. In this study, we successfully rescued the Arabidopsis (Arabidopsis thaliana) mpk4 mutant using a chemical-sensitized MPK4 variant, MPK4YG, creating a conditional activity-null mpk4 mutant named MPK4SR (genotype: PMPK4:MPK4YG mpk4) that could be used to examine the functions of MPK4 in plant growth/development and immunity. We discovered that the duration of the loss of MPK4 activity is important to plant immune responses. Short-term loss of MPK4 activity did not impact flg22-induced ROS burst or resistance against Pseudomonas syringae (Pst). Enhanced Pst resistance was only observed in the MPK4SR plants with stunted growth following prolonged inhibition of MPK4 activity. Transcriptome analyses in plants with short-term loss of MPK4 activity revealed a vital role of MPK4 in regulating several housekeeping processes, including mitosis, transcription initiation, and cell wall macromolecule catabolism. Furthermore, the constitutive weak activation of MPK4GA in the MPK4CA plants (genotype: PMPK4:MPK4GA mpk4) led to early flowering and premature senescence, which was associated with its compromised resistance against Pst. These findings suggest that MPK4 plays important roles in plant growth and development and in maintaining the delicate balance between growth/development and immune adaptation in plants.

中文翻译：

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化学致敏丝裂原活化蛋白激酶 4 有助于了解其在植物生长和免疫中的功能


以 MPK4 和 MPK3/MPK6 为最底层激酶的两个丝裂原活化蛋白激酶 （MAPK） 级联反应是植物生长/发育和免疫信号传导的关键。MPK4 级联反应的破坏会导致严重的侏儒症和自身免疫，使 MPK4 在植物生长/发育和免疫方面的研究复杂化。在这项研究中，我们使用化学致敏 MPK4 变体 MPK4YG 成功挽救了拟南芥 （Arabidopsis thaliana） mpk4 突变体，创造了一个名为 MPK4SR 的条件性无效 mpk4 突变体（基因型：PMPK4：MPK4YG mpk4），可用于检查 MPK4 在植物生长/发育和免疫中的功能。我们发现 MPK4 活性丧失的持续时间对植物免疫反应很重要。MPK4 活性的短期丧失不会影响 flg22 诱导的 ROS 爆发或对丁香假单胞菌 （Pst） 的耐药性。仅在 MPK4SR 植物中观察到增强的 Pst 抗性，在长时间抑制 MPK4 活性后生长迟缓。MPK4 活性短期丧失的植物的转录组分析揭示了 MPK4 在调节多个看家过程中的重要作用，包括有丝分裂、转录起始和细胞壁大分子分解代谢。此外，MPK4CA 植物 （基因型： PMPK4：MPK4GA mpk4） 中 MPK4GA 的组成型弱激活导致早开花和过早衰老，这与其对 Pst 的抵抗力受损有关。这些发现表明 MPK4 在植物生长发育以及维持植物生长/发育和免疫适应之间的微妙平衡中起重要作用。