Diversity of waxy gene alleles in the wild rice species of the Oryza genus

Amylose content and granule-bound starch synthase activity were measured for wild rice species (Oryza rufipogon, Oryza officinalis, Oryza meyeriana) and four widely cultivated rice varieties. The result indicates that the activity of GBSS in all rice species is positively correlated with the amylose content. The waxy gene alleles and their transcripts were cloned from three wild rice species using PCR amplification from genomic DNA or RT-PCR amplification from mRNAs of immature seeds. The waxy gene alleles of the three wild rice species and four cultivated rice varieties had different genomic DNA sequence sizes, intron-exon structures, and amino acid sequences. The predicted secondary structures of waxy proteins from the wild rice and cultivated species differed significantly. The waxy allele of O. rufipogon was most closely related to those of the cultivated rice varieties, with O. meyeriana less closely related and O. officinalis most distantly related. All of these results suggest that the allelic diversity of the waxy gene in Oryza genus is very rich. There might be different regulation mechanisms controlling amylose content by waxy genes in the wild rice species compared with the cultivated rice varieties (Oryza sativa L.).