Two Seven-Transmembrane Domain MILDEW RESISTANCE LOCUS O Proteins Cofunction in Arabidopsis Root Thigmomorphogenesis
Two Seven-Transmembrane Domain MILDEW RESISTANCE LOCUS O Proteins Cofunction in Arabidopsis Root Thigmomorphogenesis
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DOI：
10.1105/tpc.108.062653
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发表时间：
2009-07-01
期刊：
影响因子：
11.6
通讯作者：
Jones, Alan M.
中科院分区：
文献类型：
--
作者：
Chen, Zhongying;Noir, Sandra;Jones, Alan M.
根系的定向扩张受营养梯度、正向地性和向水性、负向光性和触触性以及生长轨迹中的内源振荡（环旋）的控制。系统发育相关的拟南芥基因防霉基因座 O 4 (MLO4) 和 MLO11（编码主要在根尖表达的七螺旋质膜定位蛋白）的无效突变会导致根的形态发生异常。 mlo4 和 mlo11 突变植物表现出各向异性、手性根部扩张，表现为与固体表面接触时紧密卷曲的根部图案。 mlo4 和 mlo11 突变体中的缺陷是非累加性的，并且依赖于光和营养。遗传上位实验表明，突变表型是由异源三聚体 G 蛋白复合物的 G β 亚基独立调节的。对表达的嵌合 MLO4/MLO2 蛋白的分析表明，MLO4 的 C 端结构域对于 MLO4 在根茎形态发生中的作用是必需的，但还不够。 mlo4 突变体幼苗根尖处的生长素流出载体融合体、PIN1-绿色荧光蛋白的表达、生长素诱导的基因表达模式以及顶叶和基叶生长素转运均发生改变。此外，添加生长素转运抑制剂或丧失 EIR1/AGR1/PIN2 功能可消除 mlo4、mlo11 和野生型幼苗的根卷曲。这些结果表明，mlo4 和 mlo11 突变体的夸张的根卷曲表型取决于生长素梯度，并表明 MLO4 和 MLO11 作为触摸诱导的根向性调节剂共同发挥作用。
Directional root expansion is governed by nutrient gradients, positive gravitropism and hydrotropism, negative phototropism and thigmotropism, as well as endogenous oscillations in the growth trajectory (circumnutation). Null mutations in phylogenetically related Arabidopsis thaliana genes MILDEW RESISTANCE LOCUS O 4 (MLO4) and MLO11, encoding heptahelical, plasma membrane-localized proteins predominantly expressed in the root tip, result in aberrant root thigmomorphogenesis. mlo4 and mlo11 mutant plants show anisotropic, chiral root expansion manifesting as tightly curled root patterns upon contact with solid surfaces. The defect in mlo4 and mlo11 mutants is nonadditive and dependent on light and nutrients. Genetic epistasis experiments demonstrate that the mutant phenotype is independently modulated by the G beta subunit of the heterotrimeric G-protein complex. Analysis of expressed chimeric MLO4/MLO2 proteins revealed that the C-terminal domain of MLO4 is necessary but not sufficient for MLO4 action in root thigmomorphogenesis. The expression of the auxin efflux carrier fusion, PIN1-green fluorescent protein, the pattern of auxin-induced gene expression, and acropetal as well as basipetal auxin transport are altered at the root tip of mlo4 mutant seedlings. Moreover, addition of auxin transport inhibitors or the loss of EIR1/AGR1/PIN2 function abolishes root curling of mlo4, mlo11, and wild-type seedlings. These results demonstrate that the exaggerated root curling phenotypes of the mlo4 and mlo11 mutants depend on auxin gradients and suggest that MLO4 and MLO11 cofunction as modulators of touch-induced root tropism.