Mitogen-activated protein kinase (MAPK) cascades play vital roles in regulating plant growth, development, and stress responses. MAPK-like (MPKL) proteins are a group of kinases containing the MAPK signature TxY motif and showing sequence similarity to MAPKs. However, the functions of plant MPKL proteins are currently unknown. The maize (Zea mays) genome contains four genes encoding MPKL proteins, here named ZmMPKL1 to ZmMPKL4. In this study, we show that ZmMPKL1 possesses kinase activity and that drought-induced ZmMPKL1 expression, ZmMPKL1 overexpression and knockout maize seedlings exhibited no visible morphological difference from wild-type B73 seedlings when grown under normal conditions. By contrast, under drought conditions, ZmMPKL1-overexpressing seedlings showed increased stomatal aperture, water loss, and leaf wilting and knockout seedlings showed the opposite phenotypes. Moreover, these drought-sensitive phenotypes in ZmMPKL1-overexpressing seedlings were restored by exogenous abscisic acid (ABA). ZmMPKL1 overexpression reduced drought-induced ABA production in seedlings and the knockout showed enhanced ABA production. Drought-induced transcription of ABA biosynthetic genes were suppressed and ABA catabolic genes were enhanced in ZmMPKL1-overexpressing seedlings, while their transcription were reversely regulated in knockout seedlings. These results suggest that ZmMPKL1 positively regulates seedlings drought sensitivity by altering the transcription of ABA biosynthetic and catabolic genes, and ABA homeostasis.

中文翻译：

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MAPK样蛋白1通过抑制ABA的生物合成来积极调节玉米幼苗的干旱敏感性。

丝裂原激活的蛋白激酶（MAPK）级联在调节植物生长，发育和胁迫反应中起着至关重要的作用。MAPK样（MPKL）蛋白是一组包含MAPK签名TxY基序并显示与MAPK序列相似的激酶。然而，植物MPKL蛋白的功能目前未知。玉米（Zea mays）基因组包含四个编码MPKL蛋白的基因，此处称为ZmMPKL1至ZmMPKL4。在这项研究中，我们表明ZmMPKL1具有激酶活性，并且在正常条件下生长时，干旱诱导的ZmMPKL1表达，ZmMPKL1过表达和敲除玉米幼苗与野生型B73幼苗没有可见的形态学差异。相比之下，在干旱条件下，过表达ZmMPKL1的幼苗显示出气孔孔径增加，水分流失，叶萎和敲除幼苗表现出相反的表型。此外，通过外源脱落酸（ABA）恢复了过表达ZmMPKL1的幼苗中的这些干旱敏感性表型。ZmMPKL1的过表达减少了干旱引起的幼苗中ABA的产生，而敲除表明增加了ABA的产生。ZmMPKL1过表达的幼苗受干旱诱导的ABA生物合成基因转录被抑制，ABA分解代谢基因得到增强，而在敲除苗中它们的转录被逆向调控。这些结果表明，ZmMPKL1通过改变ABA生物合成和分解代谢基因的转录以及ABA稳态来正向调节幼苗的干旱敏感性。ZmMPKL1过表达的幼苗中这些干旱敏感表型由外源脱落酸（ABA）恢复。ZmMPKL1的过表达减少了干旱引起的幼苗中ABA的产生，而敲除表明增加了ABA的产生。ZmMPKL1过表达的幼苗受干旱诱导的ABA生物合成基因转录被抑制，ABA分解代谢基因得到增强，而在敲除苗中它们的转录被逆向调控。这些结果表明，ZmMPKL1通过改变ABA生物合成和分解代谢基因的转录以及ABA稳态来正向调节幼苗的干旱敏感性。外源脱落酸（ABA）恢复了过表达ZmMPKL1的幼苗中的这些干旱敏感性表型。ZmMPKL1的过表达减少了干旱引起的幼苗中ABA的产生，而敲除表明增加了ABA的产生。ZmMPKL1过表达的幼苗受干旱诱导的ABA生物合成基因转录被抑制，ABA分解代谢基因得到增强，而在敲除苗中它们的转录被逆向调控。这些结果表明，ZmMPKL1通过改变ABA生物合成和分解代谢基因的转录以及ABA稳态来正向调节幼苗的干旱敏感性。ZmMPKL1过表达的幼苗受干旱诱导的ABA生物合成基因转录被抑制，ABA分解代谢基因得到增强，而在敲除苗中它们的转录被逆向调控。这些结果表明，ZmMPKL1通过改变ABA生物合成和分解代谢基因的转录以及ABA稳态来正向调节幼苗的干旱敏感性。ZmMPKL1过表达的幼苗受干旱诱导的ABA生物合成基因的转录被抑制，ABA分解代谢基因得到增强，而在敲除苗中它们的转录被逆向调控。这些结果表明，ZmMPKL1通过改变ABA生物合成和分解代谢基因的转录以及ABA稳态来正向调节幼苗的干旱敏感性。