CLONING AND EXPRESSION ANALYSIS OF SUCROSE-PHOSPHATE SYNTHASE FROM SUGAR-BEET (BETA-VULGARIS L)

A cDNA clone encoding a sucrose-phosphate synthase from sugar beet (Bv SPS 1) has been isolated by screening a tap root-specific cDNA library using a heterologous SPS cDNA from spinach. The 3635 bp sugar beet cD NA codes for a 1045 amino acid polypeptide with a predicted molecular mass of 118 kDa. The deduced amino acid sequence of sugar beet SPS sho ws homologies with SPS from maize (71% identity) and spinach (77% iden tity). Genomic Southern blot analysis suggests that BvSPS 1 is a low-c opy-number gene. RNA blot analysis of sink and source leaves, root and tap root tissue shows that SPS 1 is expressed in an organ-specific ma nner, being predominantly active in tap root. Incubation of detached l eaves of sugar beet in light in glucose-containing media leads to an a ccumulation of the SPS transcript, while sucrose feeding reduces the s teady-state level of the mRNA.