Abstract
Sorbitol-6-phosphate dehydrogenase (S6PDH) and NAD+-dependent sorbitol dehydrogenase (NAD+-SDH) are key enzymes in sorbitol metabolism and have been studied in many species of Rosaceae, mainly translocate sorbitol. However, sequences homologous to sorbitol-related enzymes are found in the EST clones of sucrose-translcated plants including Arabidopsis and tomato. We isolated cDNAs of tomato homologs of sorbitol-related enzymes using RT-PCR and RACE.
The cDNA of tomato S6PDH homolog (LeS6PDH) contained an ORF of 927bp capable of encording a protein of 309 amino acids. The amino acid sequence had 65%, 67% identity to apple S6PDH, celery mannose-6-phosphate reductase, respectively. LeS6PDH was probably a single copy gene and highly expressed in young leaves, stems, and fruits. The cDNA of tomato SDH homolog (LeSDH) had an ORF of 1065bp and encoded 355 amino acids. The amino acid sequence had 70-80% identity to Rosaceae NAD+-SDH. LeSDH was probably a single copy gene and highly expressed in flowers.
