Sugarbeet sucrose synthase genes differ in organ-specific and developmental expression.

A full-length sucrose synthase (SBSS2) cDNA clone was isolated from sugarbeet. Comparison of its composition and organ-specific and developmental expression with a previously isolated sugarbeet sucrose synthase gene (SBSS1) revealed distinct differences between the two genes. The two genes share 80% similarity in deduced amino acid sequence but belong to different sucrose synthase subclasses based on phylogenic analysis. Both sucrose synthases were highly expressed in roots, and had low levels of expression in leaf tissue. Transcript abundance of SBSS2, relative to SBSS1, was greater in young vegetative and floral tissues, and reduced in mature vegetative tissues. The organ-specific and developmental expression of SBSS1 and SBSS2 proteins was similar to SBSS1 and SBSS2 transcript levels, although developmental changes in protein abundance lagged transcriptional changes by many weeks. The similarities and differences in transcript and protein abundance suggest that both transcriptional and post-transcriptional regulatory mechanisms are likely to contribute to sucrose synthase expression in sugarbeet.