Benhamman Rachid, Bai Fangwen, Drory Samuel B, Loubert-Hudon Audrey, Ellis Brian, Matton Daniel P
Institut de Recherche en Biologie Végétale, Département de Sciences Biologiques, Université de Montréal, MontréalQC, Canada.
Michael Smith Laboratories, University of British Columbia, VancouverBC, Canada.
Front Plant Sci. 2017 Aug 8;8:1352. doi: 10.3389/fpls.2017.01352. eCollection 2017.
Mitogen-activated protein kinase (MAPK) signaling networks represent important means of signal transduction in plants and other eukaryotes, controlling intracellular signaling by linking perception of environmental or developmental cues to downstream targets. In the MEKK subfamily, the MKKK19, 20, and 21 form a highly supported clade with the Solanaceous Fertilization-Related Kinases. In , little is known about this group, except for MKKK20, which is involved in osmotic stress. Using a directed MKKK-MKK yeast two-hybrid (Y2H) screen, MKKK20 was found to interact only with MKK3, while a MKKK20 large-scale Y2H screen retrieved MPK18 as a direct interactant. phosphorylation assays showed that MKKK20 phosphorylates both MKK3 and MPK18. However, when all three kinases are combined, no synergistic effect is observed on MPK18 phosphorylation, suggesting a direct access to MPK18, consistent with the absence of interaction between MKK3 and MPK18 in protein-protein interaction assays. Since mutant plants were previously shown to be defective in microtubule-related functions, phenotypes of single and double mutants were investigated to determine if acts upstream of . This was the case, as root length was shorter than WT in media containing microtubule-disrupting drugs as previously observed for plants. Surprisingly, plants were also similarly affected, suggesting the presence of two non-complementary pathways involved in cortical microtubule function, the first including MKKK20, MKK3 and an unknown MPK; the second, a non-canonical MAPK cascade made of MKKK20 and MPK18 that bypasses the need for an MKK intermediate.
丝裂原活化蛋白激酶（MAPK）信号网络是植物和其他真核生物中重要的信号转导方式，通过将环境或发育信号的感知与下游靶点相连来控制细胞内信号传导。在MEKK亚家族中，MKKK19、20和21与茄科受精相关激酶形成了一个得到高度支持的进化枝。关于这个组，除了参与渗透胁迫的MKKK20外，所知甚少。通过定向的MKKK-MKK酵母双杂交（Y2H）筛选，发现MKKK20仅与MKK3相互作用，而MKKK20的大规模Y2H筛选得到MPK18作为直接相互作用蛋白。磷酸化分析表明，MKKK20使MKK3和MPK18都发生磷酸化。然而，当三种激酶组合时，未观察到对MPK18磷酸化的协同作用，这表明可直接作用于MPK18，这与蛋白质-蛋白质相互作用分析中MKK3和MPK18之间不存在相互作用一致。由于之前已证明突变体植物在微管相关功能方面存在缺陷，因此研究了单突变体和双突变体的表型，以确定是否在的上游起作用。情况确实如此，因为在含有微管破坏药物的培养基中，根长比野生型短，这与之前观察到的植物情况相同。令人惊讶的是，植物也受到类似影响，这表明存在两条参与皮层微管功能的非互补途径，第一条包括MKKK20、MKK3和一个未知的MPK；第二条是由MKKK20和MPK18组成的非经典MAPK级联，它绕过了对MKK中间体的需求。
