State Key Laboratory of Plant Physiology and Biochemistry, College of Biological Sciences, China Agricultural University, Beijing, 100193, China.
College of Plant Science, Jilin University, Changchun, 130000, China.
Plant Cell Rep. 2017 Apr;36(4):543-555. doi: 10.1007/s00299-017-2101-8. Epub 2017 Feb 2.
MKK9-MPK3/MPK6 cascade positively regulates IGSs' biosynthetic genes. Glucosinolates (GSs), secondary metabolites well known for their roles in plant defense, have been implicated to play an important role in plant abiotic stress response; however, the exact role in these processes and the underlying regulatory mechanisms remain elusive. Mitogen-activated protein kinase (MAPK) cascades are extensively involved in plant abiotic stress response. In this study, we examined the levels of four indolic glucosinolates (IGSs) in the shoots of Arabidopsis seedlings under mild osmotic stress conditions and found that 4-methoxy indolyl-3-methyl glucosinolate (4MI3G) accumulated and that MPK3 and MPK6 were activated. Loss of MPK3 or MPK6 function led to a reduction in mild osmotic stress-induced 4MI3G. Further analyses revealed that MKK9 acts upstream of MPK3 and MPK6 to promote 4MI3G accumulation. The level of 4MI3G induced by mild osmotic stress was reduced in the mkk9 mutant. Conversely, 4MI3G increased in MKK9 , a constitutively activate mutant of MKK9. Gene expression analyses indicated that the activated MKK9-MPK3/MPK6 cascade upregulates the IGS biosynthetic genes. Moreover, the lack of MYB51, the transcription factor controlling biosynthetic genes responsible for synthesizing the IGS core structure, or CYP81F2, the enzyme catalyzing core structure modification to 4MI3G, significantly reduced mild osmotic stress- and MKK9 -induced 4MI3G. Thus, our study demonstrates that mild osmotic stress promotes 4MI3G biosynthesis and the accumulation in Arabidopsis through activation of the MKK9-MPK3/MPK6 cascade and provides an MAPK-mediated signaling pathway for the IGS response to abiotic stress in plants.
MKK9-MPK3/MPK6 级联正向调控 IGSs 的生物合成基因。作为植物防御作用的次级代谢产物，硫代葡萄糖苷（GSs）已被证明在植物非生物胁迫反应中起着重要作用；然而，其在这些过程中的确切作用和潜在的调控机制仍不清楚。丝裂原活化蛋白激酶（MAPK）级联广泛参与植物非生物胁迫反应。在这项研究中，我们检测了轻度渗透胁迫条件下拟南芥幼苗地上部分的四种吲哚型硫代葡萄糖苷（IGSs）的水平，发现 4-甲氧基吲哚-3-甲基硫代葡萄糖苷（4MI3G）积累，并且 MPK3 和 MPK6 被激活。MPK3 或 MPK6 功能丧失导致轻度渗透胁迫诱导的 4MI3G 减少。进一步分析表明，MKK9 在上游作用于 MPK3 和 MPK6，促进 4MI3G 积累。在 mkk9 突变体中，轻度渗透胁迫诱导的 4MI3G 水平降低。相反，MKK9 的组成型激活突变体 MKK9 中 4MI3G 增加。基因表达分析表明，激活的 MKK9-MPK3/MPK6 级联上调 IGS 生物合成基因。此外，缺乏 MYB51（控制合成 IGS 核心结构的生物合成基因的转录因子）或 CYP81F2（催化核心结构修饰为 4MI3G 的酶），显著降低了轻度渗透胁迫和 MKK9 诱导的 4MI3G。因此，我们的研究表明，轻度渗透胁迫通过激活 MKK9-MPK3/MPK6 级联促进 4MI3G 生物合成和在拟南芥中的积累，并为 MAPK 介导的 IGS 对植物非生物胁迫的反应提供了一个信号通路。
