Abstract
Although plant roots are one of the most important organs for crop cultivation, root studies lag behind due to various difficulties. The objective of the present study was to isolate genes related to root morphology using ‘mutant panel’, rice retrotransposon Tos17-insertion mutant lines. First, we grew 5,568 R1 lines regenerated from tissue culture of Oryza sativa L. cv. Nipponbare in water culture, and screened the lines which segregated root mutants at the seedling stage. Then, 56 root mutant lines that were confirmed by the progeny test, were analyzed by genomic Southern hybridization using Tos17 as a probe. As a result of linkage analysis, we obtained one Tos17-tagged mutant line, NC6949. The phenotype of this mutant line was as follows: dwarf, narrow leaves and reduced numbers of crown roots and lateral roots. In this line, Tos17 was inserted in the third exon of the putative alliinase gene on the short arm of chromosome 1 and the presence of this insertion cosegregated with the mutant phenotype. We designated the gene tagged by Tos17, as OsAll1 (Oryza sativa alliinase 1). In a complementary experiment in which a 6kb genomic fragment containing alliinase/ORFs and its putative promoter region was introduced into the osall1 mutant, the root morphology in the transgenic plant was rescued. Based on these observations, it was concluded that the abnormal root morphology of the osall1 mutant obtained in this study was caused by knock out of the OsAll1 gene. In the rice genome, at least 3 other alliinase-like gene sequences are present and form a multigene family, but their expression patterns were different, suggesting that OsAll1 was functionally differentiated from the others.
