EFFECTS OF THE FIRST INTRON OF RICE WAXY GENE ON THE EXPRESSION OF FOREIGN GENES IN RICE AND TOBACCO PROTOPLASTS

The rice Waxy (Wx) gene codes for the starch granule-bound starch synthase, which is responsible for the synthesis of amylose in the developing endosperm and pollen. Our previous works have located the transcriptional starting site of the rice Wx gene at 1288 bp upstream of the translation initial codon and identified a 1126 bp intron (intron 1) in the 5'-untranslated region. Here we report the influence of the 5'-untranslated region including intron 1 and the area around the translational initial codon of Wx gene on the expression of GUS gene in several chimeric constructs in rice and tobacco protoplasts. The GUS activity in rice and tobacco protoplasts transformed with the chimeric gene, pWG3.4 plasmid, was much higher than that of a construct with 1.3-kb 5' untranslated region deleted. When Wx intron 1 was inserted into the site between the CaMV 35S promoter and GUS coding sequence, the GUS activity was increased about 15-fold in rice protoplasts, but with practically no effect in tobacco mesophyllous protoplasts. Sequence analyses of RNAs transcribed from pWG3.4 plasmid DNA in protoplasts showed that the intron 1 of the Wx gene was spliced accurately both in rice protoplasts and in tobacco mesophyllous protoplasts.