Genetic analysis and identification of alarge leaf angles (lla) mutant in rice

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Mutants are essential genetic materials to elucidation of biological functions of genes involved. Characterization and isolation of genes in mutants is one of the research tasks in functional genomic era. T-DNA insertional mutagenesis has provided an efficient way to identify genes in plant species, in which the mutated genes could be rapidly isolated once the mutant was confirmed by T-DNA insertion. About 40% of 620 cloned Arabidopsis genes with mutant phenotypes were determined by T-DNA tagging. In recent years, a large number of T-DNA insertional rice mutant pools were established. Moreover, three genes were successfully isolated from rice. Leaf angles, the angles between main culms and leaves, are one of the important features of the plant types. Investigation on the mechanism of leaf angle formation will probably provide the basic knowledge of plant breeding on plant architectures. Several QTLs of leaf and flag leaf angles in rice were identified, which would provide the useful materials for manipulating these QTLs in a marker-assisted selection program. However, the major genes, which control leaf angles, have not been reported yet and very little is known about the mechanism of leaf angle formation. Based on T-DNA inserted rice (Oryza sativa L. subsp. Japonica cv. Zhonghua11) mutant pool, which contains about 10000 insertional mutant lines, a large leaf angles (lla) mutant T429 was found in T1 lines. At seeding stage, the leaf angles of lla mutant were larger than those of the wild type. In addition, the mutant seedlings showed semi-dwarf. At heading stage, the abnormal phenotypes of lla mutants were observed in plant height, leaf angel, leaf blade length and leaf blade width. The plant of lla was shorter than the wild type (Fig. 1). The length and width of the lla mutant leaves were shorter and wider than those of the wild type (unpublished data). Under natural long day conditions, the heading date of lla was about two weeks later than that of the wild type. Under winter natural short day conditions in greenhouse, the heading date of lla was about one week later than that of the wild type while the plant height and leaf angles remained significantly different from the control. This indicated that the mutant phenotype was slightly influenced by environmental conditions such as photoperiod and temperature. Different concentrations of GA3 were used to treat the plants at both seeding and heading stages; the results showed that the plant heights of wild type and the lla mutant were all sensitive to exogenous GA3 at different concentrations. But plant heights and leaf angles of GA3 treated mutant plants differed significantly from the corresponding wild types. At the same time, leaf angles of GA3 treated wild type and lla did not show any visible differences from the corresponding untreated plants.