Ca2+-dependent GTPase, Extra-large G Protein 2 (XLG2), Promotes Activation of DNA-binding Protein Related to Vernalization 1 (RTV1), Leading to Activation of Floral Integrator Genes and Early Flowering in Arabidopsis
Ca2+-dependent GTPase, Extra-large G Protein 2 (XLG2), Promotes Activation of DNA-binding Protein Related to Vernalization 1 (RTV1), Leading to Activation of Floral Integrator Genes and Early Flowering in Arabidopsis
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DOI：
10.1074/jbc.m111.317412
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发表时间：
2012-03-09
影响因子：
4.8
通讯作者：
Assmann, Sarah M.
中科院分区：
文献类型：
--
作者：
Heo, Jae Bok;Sung, Sibum;Assmann, Sarah M.
异源三聚体G蛋白由G α、G β和G γ亚基组成，在植物发育和细胞信号传导中起重要作用。在拟南芥中，除了一个典型的G蛋白α亚基GPA 1外，还有三个超大型G蛋白XLG 1、XLG 2和XLG 3，其功能在很大程度上未知。每个超大G（XLG）蛋白具有C-末端G α样区域和类似于400个氨基酸的N-末端延伸。在这里，我们表明，三个XLG蛋白特异性结合和水解GTP，尽管事实上，这些植物特异性蛋白缺乏关键的保守氨基酸残基的GTP结合和水解的GTP在哺乳动物G α蛋白。此外，与其他已知的G α蛋白不同，这些活性需要Ca 2+而不是Mg 2+作为辅因子。酵母双杂交文库筛选和体外蛋白质下拉分析显示，XLG 2与核蛋白RTV 1（与春化1相关）相互作用。电泳迁移率变动分析表明，RTV 1在体外以非序列特异性方式与DNA结合，而GTP结合的XLG 2促进RTV 1的DNA结合活性。RTV 1的过表达导致提早开花。XLG 2和RTV 1的组合过表达增强了这种早期开花表型，并提高了花途径整合基因FT和SOC 1的表达，但不抑制花阻遏物FLC的表达。染色质免疫沉淀分析表明，XLG 2增加RTV 1结合FT和SOC 1启动子。因此，Ca 2+依赖的G蛋白，XLG 2，促进RTV 1 DNA结合活性的花整合子基因的子集，并有助于花的转变。
Heterotrimeric G proteins, consisting of G alpha, G beta, and G gamma sub-units, play important roles in plant development and cell signaling. In Arabidopsis, in addition to one prototypical G protein alpha subunit, GPA1, there are three extra-large G proteins, XLG1, XLG2, and XLG3, of largely unknown function. Each extra-large G (XLG) protein has a C-terminal G alpha-like region and a similar to 400 amino acid N-terminal extension. Here we show that the three XLG proteins specifically bind and hydrolyze GTP, despite the fact that these plant-specific proteins lack key conserved amino acid residues important for GTP binding and hydrolysis of GTP in mammalian G alpha proteins. Moreover, unlike other known G alpha proteins, these activities require Ca2+ instead of Mg2+ as a cofactor. Yeast two-hybrid library screening and in vitro protein pull-down assays revealed that XLG2 interacts with the nuclear protein RTV1(related to vernalization 1). Electrophoretic mobility shift assays show that RTV1 binds to DNA in vitro in a non-sequence-specific manner and that GTP-bound XLG2 promotes the DNA binding activity of RTV1. Overexpression of RTV1 results in early flowering. Combined overexpression of XLG2 and RTV1 enhances this early flowering phenotype and elevates expression of the floral pathway integrator genes, FT and SOC1, but does not repress expression of the floral repressor, FLC. Chromatin immunoprecipitation assays show that XLG2 increases RTV1 binding to FT and SOC1 promoters. Thus, a Ca2+-dependent G protein, XLG2, promotes RTV1 DNA binding activity for a subset of floral integrator genes and contributes to floral transition.