24. Differential regulation of waxy gene expression in rice

The evidence being accumulated shows that the genome of higher organisms appears to contain substantial amounts of genetic factors regulating the timing, place, and quantity of production of various gene products leading to diversified phenotypes. In order to examine the effects of different alleles on the gene expression at the waxy locus, the Wx gene product which controls the synthesis of amylose was isolated from endosperm starch of rice plants and analysed by electrophoretic techniques. The major protein (about 60,000 daltons) was absent in most of waxy strains and increased with the number of Wx alleles in triploid endosperms, suggesting that the major protein was the Wx gene product. In addition to wx alleles which result in the absence or drastic reduction of the Wx gene product and amylose, differentiation of Wx alleles seemed to have occurred among non-glutinous rice strains. At least two Wx alleles, Wx^a and Wx^b differing in efficiency in the production of the major protein as well as of amylose were detected.

Of special interest is the presence of different alleles, Wx^a and Wx^b, which regulate the quantitative level of the gene product. The two alleles may be regarded as the result of a mutation at a regulatory site(s) at or near the structural gene. Thus, biochemical approaches to the study of Wx protein in rice may throw more light on not only an important quality trait but also regulatory mechanisms of gene expression in rice. I intend to investigate whether the level of Wx protein is well correlated with amylose content in endosperm starch by using various induced mutants.