Molecular characterization and expression of three galactinol synthase genes that confer stress tolerance in Salvia miltiorrhiza.

To adapt to changes in their growing environment, plants express several stress-responsive genes. For example, the products of galactinol synthase (Gols) genes play a key role in regulating the levels of raffinose family oligosaccharides and conferring resistance to stress. We cloned and characterized three Gols genes in Salvia miltiorrhiza. Their expression followed three distinct patterns. Compared with the control, SmGols1 was up-regulated by temperature changes but was suppressed by exposure to methyl jasmonate or short-term drought. This gene had the greatest abundance of transcripts and was assigned a general function of carbon storage. SmGols2 responded to all stress and hormone treatments, and transcripts were maintained at a high level. Finally, expression of SmGols3 was weaker than the other two genes, but was increased significantly under different treatments. Over the experimental period, its expression declined to normal levels in response to all treatments except exposure to 100 μM ABA, long-term drought, heat (42 °C), or chilling (8 °C). Based on our finding of cis-elements in the 5' flanking regions, we concluded that these genes seem to be regulated by several HSF transcription factors. We also targeted their 90-bp conserved sequences and used them for RNA interference analysis. Some were knocked down to various extents in our transgenic lines. Fluctuations in their malondialdehyde contents under different stress treatments, as well as the rate of water loss in transformed plants, suggested that lipid peroxidation was more likely to occur in the transgenics than in the control. These results indicate that SmGols genes could have a main function in responding to cold or heat. Therefore, we believe that it is important to investigate this mechanism for tolerance in S. miltiorrhiza and to examine how expression of these SmGols and other homologs are influenced by abiotic stresses.