Matsuoka Daisuke, Yasufuku Takuto, Furuya Tomoyuki, Nanmori Takashi
Graduate School of Agricultural Science, Kobe University, 1-1 Rokkodai-cho, Nada-ku, Kobe, Hyogo, 657-8501, Japan,
Plant Mol Biol. 2015 Apr;87(6):565-75. doi: 10.1007/s11103-015-0295-0. Epub 2015 Feb 14.
Abscisic acid (ABA) is a phytohormone that regulates many physiological functions, such as plant growth, development and stress responses. The MAPK cascade plays an important role in ABA signal transduction. Several MAPK and MAPKK molecules are reported to function in ABA signaling; however, there have been few studies related to the identification of MAPKKK upstream of MAPKK in ABA signaling. In this study, we show that an Arabidopsis MAPKKK, MAPKKK18 functions in ABA signaling. The expression of MAPKKK18 was induced by ABA treatment. Yeast two-hybrid analysis revealed that MAPKKKK18 interacted with MKK3, which interacted with C-group MAPK, MPK1/2/7. Immunoprecipitated kinase assay showed that the 3xFlag-tagged MAPKKK18, expressed in Arabidopsis plants, was activated when treated with ABA. These results indicate the possibility that the MAPK cascade is composed of MAPKKK18, MKK3 and MPK1/2/7 in ABA signaling. The transgenic plants overexpressing MAPKKK18 (35S:MAPKKK18) and its kinase negative mutant (35S:MAPKKK18 KN) were generated, and their growth was monitored. Compared with the WT plant, 35S:MAPKKK18 and 35S:MAPKKK18 KN showed smaller and bigger phenotypes, respectively. Senescence of the rosette leaves was promoted in 35S:MAPKKK18, but suppressed in 35S:MAPKKK18 KN. Furthermore, ABA-induced leaf senescence was accelerated in 35S:MAPKKK18. These results suggest that MAPKKK18 controls the plant growth by adjusting the timing of senescence via its protein kinase activity in ABA dependent manners.
脱落酸（ABA）是一种植物激素，可调节多种生理功能，如植物生长、发育和应激反应。丝裂原活化蛋白激酶（MAPK）级联在ABA信号转导中起重要作用。据报道，几种MAPK和MAPKK分子在ABA信号传导中发挥作用；然而，关于ABA信号传导中MAPKK上游的MAPKKK的鉴定研究较少。在本研究中，我们表明拟南芥MAPKKK，即MAPKKK18在ABA信号传导中起作用。ABA处理可诱导MAPKKK18的表达。酵母双杂交分析表明，MAPKKKK18与MKK3相互作用，而MKK3与C组MAPK，即MPK1/2/7相互作用。免疫沉淀激酶分析表明，在拟南芥植物中表达的3xFlag标记的MAPKKK18在用ABA处理时被激活。这些结果表明，在ABA信号传导中，MAPK级联可能由MAPKKK18、MKK3和MPK1/2/7组成。我们构建了过表达MAPKKK18（35S:MAPKKK18）及其激酶负突变体（35S:MAPKKK18 KN）的转基因植物，并监测了它们的生长情况。与野生型植物相比，35S:MAPKKK18和35S:MAPKKK18 KN分别表现出较小和较大的表型。35S:MAPKKK18中莲座叶的衰老得到促进，而在35S:MAPKKK18 KN中则受到抑制。此外，35S:MAPKKK18中ABA诱导的叶片衰老加速。这些结果表明，MAPKKK18通过其蛋白激酶活性以ABA依赖的方式调节衰老时间来控制植物生长。
