摘要
植物根具有吸收水分和养分、固定植株和合成激素等作用。因为土壤中水分和养分常受到限制，所以根系在土壤中的空间分布如根的构型很大程度上决定了植物吸收水分和养分的能力。而根的长度是根型的主要参数，对于养分的吸收，耐旱和作物的产量都有重要的作用。要揭示控制根伸长的遗传和分子机理，利用根的突变体是一个有效的方法。本研究利用T-DNA插入的水稻突变体库，筛选到一个新颖的水稻短根突变体sr1，并进行了初步的研究。
短根突变体sr1在苗期表现为初生根极短，根细，但在溶液培养约35天后，根能恢复到野生型一样的长度。组织切片发现突变体sr1短根表型是因为在根尖的分生区细胞数目减少和各种类型细胞的径向直径减小所造成。
克隆到了控制短根的基因OsGLR1，OsGLR1基因与动物和拟南芥离子通道型谷氨酸受体基因同源，编码4个跨膜结构域M1、M2、M3和M4，2个配体结合结构结构域GlnH1和GlnH2。Sounthern印迹表明OsGLR1基因为单拷贝，它有6个外显子组成，位于第4染色体上。
通过转基因互补能大部分恢复短根突变体sr1的根长，证实了OsGLR1基因控制根伸长的功能；短根突变体sr1的根尖分生区细胞内钙离子浓度比野生型显著低；蛋白免疫分析发现OsGLR1是一分子量约110kDa的膜整合蛋白；OsGLR1基因主要在侧根、根和叶的维管组织中表达；说明OsGLR1可能是一个钙转运的离子通道。
在36／30℃高温培养7天时，短根突变体根要比在28／22℃下伸长快近2倍，在水稻培养液中能达到野生型根长的约90％，而野生型的根伸长在这二种温度培养时几乎一样，表现出高温抑制。说明短根突变体sr1对高温不敏感表现为耐高温特性，OsGLR1基因可能参与了温度调控根伸长的反应。
The plant roots are involved in the acquisition of water and nutrients, anchorage of plants, synthesis of plant hormones. Because the supplies of nutrition and water in soil are always limited, the spatial distribution of the root system, i.e., root architecture, largely determines the ability of a plant to exploit these resources. The root length is main parameter of root architecture with various important functions such as nutrient uptake, drought tolerance and yield. To uncover the mechanisms controlling root elongation, genetic analysis of mutants have been proved to be a useful approach. We isolated a novel short root mutant, sr1, from an T1 population of rice japonica variety Zhonghua No. 11generated by T-DNA mutagensis.
The mutant srl shows greatly reduced primary root length and diameter at the seedling stage. Hydroponic cultivation revealed that root length of the mutant recovers to the level of the wild type at about 35 days. Histological observation of seminal root tips indicated that the short root phenotype was due to the reduced cell number and cell expansion.
The gene, OsGLRl, controlling the short root phenotype was cloned after genetic analysis, and identified as a homolog ionotropic glutamate receptors (iGluRs) gene. Because it encodes all of signature domains of animal and Araidopsis iGluRs, including four transmember domains (Ml to M4) and the putative ligand-hinding domains(GlnHl and GlnH2). Southern blotting analysis indicates that itis a single copy gene in rice genome. OsGLRl gene is consisted of six exons and mapped on chromosome 4.
Genetic complementation analysis proved the function of OsGLRl gene to elongate the root length. The level of Ca2+ in meristem of srl root tip decreased significantly compared with wild type. The promoter of OsGLRl gene was active in lateral root and vascular tissues in root and leaf. This suggests that OsGLRl may encode a function channel that unloads or allocatas Ca2+.
When grown at 36/30, srl seedings exibit dramatic root elongation compared with seeding grown at 28/22, and attain the 90% root length of wild type in rice culture solution. So srl is insensitivity and tolerance to high temperature and OsGLRl may involed in controlling temperature-mediated root elongation.
引文
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