A Short Root Mutant Of Rice In Seedling Mutagenized By T-DNA Insertion

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.