2003 Volume 78 Issue 2 Pages 127-138
In the present study, we identified and characterized two cDNAs, named TaGA1 and TaGA2, encoding α subunits of heterotrimeric G proteins synthesized from one-week-old seedling mRNAs of common wheat cv. S615 using RACE PCR and RT-PCR methods. The clone TaGA1 contained an open reading frame that encoded a protein consisting of 383 amino acid residues with a molecular mass of 51.3 kDa, whereas the clone TaGA2 contained an open reading frame encoding 390 amino acids with a molecular mass of 52.5 kDa. At the amino acid level, both cDNAs (TaGA1 and TaGA2) showed 70-96% and 30-40% homologies to plant and animal G-protein alpha (G α) subunits, respectively, and 97.7% homology to each other. The regions essential for binding to GTP were conserved among all G α subunits in higher plants and mammals examined. However, the C-terminal amino acid sequences of TaGA1 and TaGA2 were similar to those of cereal G α subunits (rice and barley) but were different from the analogous sequences of mammalian G α subunits as well as from those of the leguminous and Solanaeceous G α subunits. Southern analysis revealed that the hexaploid wheat genome contained three major copies of G α subunit gene with a few less homologous copies. The analysis of the expression for G α subunit genes in wheat showed that both TaGA1 and TaGA2 mRNAs were abundant in one-week-old seedlings, immature seeds harvested one-week after anthesis, young spikes and internodes, indicating constitutive expression patterns in all of the organs tested. Especially, young spikes and internodes exhibited increased levels of mRNA accumulation, suggesting that G α subunit gene is highly expressed in actively elongating and fast growing tissues. Moreover, both TaGA1 and TaGA2 showed genome-specific expressions in wheat and may participate in the light-regulated growth and development of the seedlings.