Structure and RFLP mapping of a rice sucrose phosphate synthase (SPS) gene that is specifically expressed in the source organ

A rice sucrose phosphate synthase (SPS) gene was isolated and mapped on chromosome 1, based upon RFLPs be tween a japonica line 'FL134' and an indica cultivar 'Kasalath'. This gene consisted of 12 exons with 11 introns. In the exon 1, an additional sequence occurred bearing an insertion encoding 24 glycine residues when it was compared with the spinach one. Although the structure of this region possessed the consensus intron borders, its size was only 48 bp and it occurred with neither breakage of open reading frame nor shift of the reading frame. The deduced amino acid sequence of the rice SPS showed a high degree of homology to the known ones. Sites for modification by kinase/phosphatase and for binding with UDP-glucose were highly conserved. No typical promoter sequences were found upstream of the coding region, suggesting that function of the promoter of this gene is weak, although further upstream of the coding region, sequences similar to the promoter and light-responsive elements were found. Expression of this gene was detected only in the leaves, suggesting that this gene is specifically expressed in the source organs. Level of expression was extremely low, reflecting weakness of its promoter activity.