Effects of sorbitol on expression of genes involved in regeneration of upland rice (Oryza sativa L.)

Sorbitol promotes plantlet regeneration frequency (PRF) of rice calli. To better understand this phenomenon, calli of upland rice cv. HD65 were induced on medium containing 10 g sorbitol/L, and subcultured and regenerated on media containing 20 and 40 g sorbitol/L, respectively. Using complementary DNA (cDNA)-amplified fragment length polymorphism (AFLP) analysis, we investigated differential gene expression between sorbitol-supplemented (SC) and sorbitol-free calli (NC) during the regeneration stage. From >4,000 transcript-derived fragments (TDFs), we identified 118 differentially expressed TDFs between SC and NC. Of these, 37 were cloned and sequenced, and 12 were further confirmed by semiquantitative reverse-transcription polymerase chain reaction (RT-PCR) analysis. Database searches indicated that 10 TDFs showed no significant homology to genes with known or putative functions, although they were previously reported to be expressed in rice calli. These cDNAs might encode novel proteins related to plantlet regeneration. Of all the 27 well-known TDFs, 35.1% were highly expressed in SC, and had roles in signal transduction (13.5%), transcription and translation (13.5%), and regulation (8.1%). Four TDFs were related to plant growth and regeneration: TDF5, TDF17, TDF21, and TDF26, which showed homologies to a nucleoside diphosphate kinase (NDPK), a cyclin, a receptor-like protein kinase precursor, and TCP-1, respectively. Furthermore, 35.1% were related to metabolism, 27.0% to energy, and 8.1% to defense. These results suggest that, in addition to its roles as a carbon source and an osmotic regulator, sorbitol may also act as a chemical signal to directly or indirectly alter gene expression. Sorbitol exerts its effects via complex transcriptional networks to enhance PRF of calli.