Department of Botany, University of British Columbia, Vancouver, BC V6T 1Z4, Canada.
Michael Smith Laboratories, University of British Columbia, Vancouver, BC V6T 1Z4, Canada.
Plant Physiol. 2018 Nov;178(3):1284-1295. doi: 10.1104/pp.18.00592. Epub 2018 Sep 5.
Arabidopsis () MAP KINASE (MPK) proteins can function in multiple MAP kinase cascades and physiological processes. For instance, MPK4 functions in regulating development as well as in plant defense by participating in two independent MAP kinase cascades: the MEKK1-MKK1/MKK2-MPK4 cascade promotes basal resistance against pathogens and is guarded by the NB-LRR protein SUMM2, whereas the ANPs-MKK6-MPK4 cascade plays an essential role in cytokinesis. Here, we report a novel role for MKK6 in regulating plant immune responses. We found that MKK6 functions similarly to MKK1/MKK2 and works together with MEKK1 and MPK4 to prevent autoactivation of SUMM2-mediated defense responses. Interestingly, loss of MKK6 or ANP2/ANP3 results in constitutive activation of plant defense responses. The autoimmune phenotypes of and mutant plants can be largely suppressed by a constitutively active mutant. Further analysis showed that the constitutive defense response in is dependent on the defense regulators PAD4 and EDS1, but not on SUMM2, suggesting that the ANP2/ANP3-MKK6-MPK4 cascade may be guarded by a TIR-NB-LRR protein. Our study shows that MKK6 has multiple functions in plant defense responses in addition to cytokinesis.
拟南芥（Arabidopsis）MAP 激酶（MPK）蛋白可在多个 MAP 激酶级联和生理过程中发挥作用。例如，MPK4 通过参与两个独立的 MAP 激酶级联反应：MEKK1-MKK1/MKK2-MPK4 级联反应来调节发育以及植物防御，该级联反应促进对病原体的基础抗性，并受到 NB-LRR 蛋白 SUMM2 的保护，而 ANPs-MKK6-MPK4 级联反应则在细胞分裂中起着重要作用。在这里，我们报道了 MKK6 在调节植物免疫反应中的新作用。我们发现 MKK6 的功能类似于 MKK1/MKK2，并与 MEKK1 和 MPK4 一起共同防止 SUMM2 介导的防御反应的自动激活。有趣的是，缺失 MKK6 或 ANP2/ANP3 会导致植物防御反应的组成性激活。组成型激活的 突变体可以在很大程度上抑制 和 突变体的自身免疫表型。进一步的分析表明，中组成性防御反应依赖于防御调节剂 PAD4 和 EDS1，但不依赖于 SUMM2，这表明 ANP2/ANP3-MKK6-MPK4 级联反应可能受到 TIR-NB-LRR 蛋白的保护。我们的研究表明，MKK6 在细胞分裂以外的植物防御反应中具有多种功能。
