;The Waxy (Wx) gene encodes a granule-bound starch synthase (GBSS) that plays a key role in the amylose synthesis of rice and other plant species. Two functional Wx alleles of rice exist: Wx a , which produces a large amount of amylose, and Wx b , which produces a smaller amount of amylose because of the mutation at the 5¢ splice site of intron 1. Wx b is largely distributed in Japonica cultivars, and high amylose cultivars do not exist in Japonica cultivars. We introduced the cloned Wx a cDNA into null-mutant Japonica rice (wx). The amylose contents of these transgenic plants were 6-11% higher than that of the original cultivar, Labelle, which carries the Wx a allele, although the levels of the Wx protein in the transgenic rice were equal to those of cv. Labelle. We also observed a gene-dosage effect of the Wx a transgene on Wx protein expression, but a smaller dosage effect was observed in amylose production with over 40% of amylose content in transgenic rice. Moreover, one transgenic line carrying eleven copies of the transgene showed low levels of Wx expression and amylose in the endosperm. This suggested that the integration of excessive copies of the transgene might lead to gene silencing.
Treatment with 5-azacytidine, a DNA demethylating reagent, induced flowering in Perilla frutescens (L.) Britton var. crispa (Thunb. ex Murray) Decne. ex L. H. Bailey, an absolute short-day plant under long days. The 5-azacytidine treatment induced slight suppression of vegetative growth but had no obvious effect on any other phenotypes. The Southern hybridization analysis of the genomic DNA isolated from the leaves of 5-azacytidine-treated plants and digested with restriction enzyme, methylation-insensitive Msp I or methylation-sensitive Hpa II with P. frutescens 25S-18S rDNA intergenic spacer probe indicated that the 5-azacytidine treatment caused demethylation of the genomic DNA. The 5-azacytidine-induced flowering was delayed as compared with the short day-induced flowering. Flowers were formed even at the lower nodes which had not been directly treated with 5-azacytidine. The results suggest that DNA demethylation induced flowering by inducing the production of a transmissible flowering stimulus in P. frutescens.
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