State Key Laboratory of Agricultural Microbiology, College of Life Science and Technology, Huazhong Agricultural University, Wuhan, 430070, China.
Department of Plant, Soil and Entomological Sciences and Program of Microbiology, Molecular Biology and Biochemistry, University of Idaho, Moscow, ID, 83844, USA.
Sci China Life Sci. 2019 Sep;62(9):1203-1217. doi: 10.1007/s11427-018-9444-9. Epub 2019 Jan 25.
Symbiosis receptor-like kinase (SymRK) is a key protein mediating the legume-Rhizobium symbiosis. Our previous work has identified an MAP kinase kinase, SIP2, as a SymRK-interacting protein to positively regulate nodule organogenesis in Lotus japonicus, suggesting that an MAPK cascade might be involved in Rhizobium-legume symbiosis. In this study, LjMPK6 was identified as a phosphorylation target of SIP2. Stable transgenic L. japonicus with RNAi silencing of LjMPK6 decreased the numbers of nodule primordia (NP) and nodule, while plants overexpressing LjMPK6 increased the numbers of nodule, infection threads (ITs), and NP, indicating that LjMPK6 plays a positive role in nodulation. LjMPK6 could interact with a cytokinin receptor, LHK1 both in vivo and in vitro. LjMPK6 was shown to compete with LHP1 to bind to the receiver domain (RD) of LHK1and to downregulate the expression of two LjACS (1-aminocyclopropane-1-carboxylic acid synthase) genes and ethylene levels during nodulation. This study demonstrated an important role of LjMPK6 in regulation of nodule organogenesis and ethylene production in L. japonicus.
共生受体样激酶（SymRK）是一种介导豆科植物-根瘤菌共生的关键蛋白。我们之前的工作已经鉴定出一种 MAP 激酶激酶 SIP2 是 SymRK 的互作蛋白，可正向调控百脉根的根瘤器官发生，这表明 MAPK 级联可能参与根瘤菌-豆科植物共生。在本研究中，鉴定到 LjMPK6 是 SIP2 的磷酸化靶标。通过 RNAi 沉默稳定转化的 LjMPK6 减少了根瘤原基（NP）和根瘤的数量，而过表达 LjMPK6 的植株增加了根瘤、侵染线（IT）和 NP 的数量，表明 LjMPK6 在结瘤过程中发挥积极作用。LjMPK6 可以在体内和体外与细胞分裂素受体 LHK1 相互作用。研究表明 LjMPK6 与 LHP1 竞争结合 LHK1 的受体结构域（RD），并下调两个 LjACS（1-氨基环丙烷-1-羧酸合酶）基因的表达和结瘤过程中的乙烯水平。本研究表明 LjMPK6 在调控百脉根根瘤器官发生和乙烯产生中具有重要作用。
