TRANSCRIPTOMIC ANALYSIS OF LEAVES OF TRANSGENIC APPLE SILENCED FOR SORBITOL-6-PHOSPHATE DEHYDROGENASE GENE

Plants in the Rosaceae synthesize both sorbitol and sucrose as major end products of photosynthesis. Sorbitol helps determine fruit and vegetative quality. To clarify the mechanism through which sorbitol acts as a signal molecule, we conducted comprehensive analyses of genes regulated by sorbitol in mature leaves of transgenic apple (Malus × domestica Borkh. ‘Greensleeves’) that were silenced for the sorbitol-6-phosphate dehydrogenase (S6PDH) gene. The microarray was designed using 23,731 apple unigenes opened by NCBI (http://www.ncbi.nlm. nih.gov/). Trees of sense clone GSS78 and antisense clone GSA04 had reduced S6PDH transcript compared to an untransformed control. In GSA04, 138 down-regulated (<0.5-fold) and 121 up-regulated genes (>2-fold) were identified. In GSS78, 2,687 down-regulated genes (<0.5-fold) were identified, 100 of which were also down-regulated in GSA04. In GSS78, 2,718 up-regulated genes (>2-fold) were identified, 70 of which were also up-regulated in GSA04. Expression of these genes may be directly or indirectly regulated by sorbitol. Analysis of GO terms revealed that, among down-regulated genes in GSA04 involved in biological processes, the represented categories included “oxidation reduction”, “response to stress”, “primary metabolic process”, “response to hormone stimulus”, “regulation of transcription, DNA-dependent”, “cellular macromolecule metabolic process”, and “regulation of cellular process”. The functions of the drastically up-regulated genes are unknown except for sorbitol metabolism. These results are a first step toward functional genomics research for understanding gene functions and regulatory networks upon which sorbitol act as a signal molecule, affecting fruit quality and growth.