Suppressive expression of the glutelin A1-collagen peptide fusion gene in hybrid rice lines with the mutant line, Low Glutelin Content-1 (LGC-1)

A low glutelin-content mutant, LGC-1, has a mutant gene (lgc1) comprising a tail-to-tail inverted repeat of two highly homologous glutelin B genes (gluB4 and δ-gluB5), resulting in the production of double-stranded glutelin B RNA. Hybrid rice lines between LGC-1 and a transgenic line with the glutelin A1-collagen peptide fusion gene (gluA1-coll) were produced, and F2 hybrid lines homozygous for each or both of the gluA1-coll and lgc1 genes were selected. The expression of gluA1-coll in F2 lines with lgc1 was far lower than that of F2 lines without lgc1 at both the mRNA and protein levels as measured by semi-quantitative RT-PCR and immunoblotting using anti-collagen peptide antibody. The gluA1 mRNA sequence alignment identical to the potential double-stranded RNA formed by gluB4 sense and δ-gluB5 antisense RNAs consisted of 14 nucleotides at most, and was not more than 23 even when one mismatch was allowed within the sequence. Thus, such shorter double-stranded glutelin B RNAs were suggested to suppress the expression of not only endogenous gluA genes as reported previously (Kusaba et al. 2003) but also the exogenous gluA1-coll in the hybrid lines.