Cloning and transcriptional regulation of Sdrac encoding a Rac/Rop small guanosine 5'-triphosphate-binding protein gene from Scoparia dulcis

A cDNA clone designated Sdrac (965 bp) was isolated from the seedlings of Scoparia dulcis. This gene contains an open reading frame encoding the protein of 196 amino acid residues with high homology to Rac/Rop small GTPases from various plant sources. In Southern hybridization analysis, the partial hydrolysates of genomic DNA of S. dulcis prepared by the digestion with XbaI, XhoI, or EcoRI showed one main band together with a few weakly hybridized signals. The change in the transcriptional activity of Sdrac was analyzed by RT-PCR under various conditions, and it showed a marked increase by the treatment of the leaf tissues of the plant with methyl jasmonate and 2-chloroethylphosphonic acid, an ethylene-generating reagent. However, no significant change in the expression activity was observed upon the treatment of the leaves with Ca2+-ionophore A23187. Treatment of the leaves with high concentration of NaCl also did not affect the expression level of the gene. These results suggest the possibility that Sdrac product plays roles in a certain cellular event in the signal transduction processes evoked by methyl jasmonate and ethylene accompanying the change in the transcriptional activity.