CDNA CLONING AND TISSUE-SPECIFIC EXPRESSION OF A GENE FOR SUCROSE TRANSPORTER FROM RICE (ORYZA-SATIVA L.)

We describe the cloning and expression analysis of a sucrose transport er cDNA from a monocot (the rice plant, Oryza sativa L.). The cDNA clo ne (OsSUT1) encoded an open reading frame of 1,611 bp (537 amino acids ) and showed 76.8 to 79.7% similarity at the amino acid level to other sucrose transporters of dicot species, The predicted membrane topolog y of OsSUT1 protein is made up of 12 transmembrane helices which is co nsistent with most of the mono-and disaccharide transporters previousl y identified, When OsSUT1 cDNA was introduced into yeast and expressed , the cells rapidly accumulated sucrose demonstrating that OsSUT1 does , in fact, encode a sucrose transporter, From genomic Southern hybridi zation OsSUT1 appeared to be a single copy gene, OsSUT1 was expressed in source organs such as leaf blade, leaf sheath and germinating seed whereas little or no expression was observed in some sink organs such as the panicles before heading and the roots. Transcript was observed at high levels in panicles after heading, particularly in the portion containing endosperm and embryo. In addition, expression of OsSUT1 was high in etiolated seedlings and decreased during light-induced greeni ng.