Characterization of a rice sucrose-phosphate synthase-encoding gene.

A rice genomic clone (sps1) coding for sucrose phosphate synthase (SPS) was isolated and sequenced. Rice sps1 contains 13 exons and 12 introns, an unusually long 366-bp leader region with a highly organized primary structure and a promoter region with no obvious homology with eukaryotic promoter consensus sequences. Southern blot analysis showed that SPS is encoded by a single-copy gene in the rice genome. Comparison of the rice, maize, potato and spinach SPS deduced amino acid (aa) sequences showed that these enzymes have a well conserved region comprising their first 700 aa, and a variable C-terminal region. Analysis of rice sps1 expression showed that mRNA levels change during leaf development. SPS activity and mRNA were undetectable in roots.