Plant & Animal Genomes XI Conference

January 11-15, 2003
Town & Country Convention Center
San Diego, CA

Poster: Gene Isolation
            

CLONING AND CHARACTERIZATION OF cDNAs ENCODING α AND β SUBUNITS OF HETEROTRIMERIC G-PROTEIN IN COMMON WHEAT ( TRITICUM aestivum )

¹ Lab. of Genetics and Plant Breeding, Graduate School of Science and Technology, Faculty of Horticulture, Chiba University, 648 Matsudo, Matsudo city, Chiba 271-8510, Japan

² Faculty of Horticulture, Chiba University, 648 Matsudo, Matsudo city, Chiba 271-8510, Japan

³ Faculty of Horticulture, Chiba University, 648 Matsudo, Matsudo city, Chiba 271-8510, Japan

Plant heterotrimeric G protein, which consist of α, β and γ sub-units, play an important key role for plant growth and development through various signalling pathways and that transfer the signals from the G protein-coupled receptors (GPCRs) to effector molecules. In the present investigation, we cloned and characterized two full-length cDNAs (TaGA1 and TaGA2) encoding α subunits and a full-length cDNA (TaGB1) encoding β subunit of heterotrimeric G protein, synthesized from one-week old seedling mRNAs from common wheat cv. S615 by RT-PCR and RACE PCR method. The clone TaGA1 contained an open reading frame that encoded a protein of 383 amino acid residues with molecular mass of 51.3 kDa, whereas the clone TaGA2 contained an open reading frame of 390 amino acids with mol. mass of 52.5 kDa. At the amino acid level, both cDNAs (TaGA1 and TaGA2) showed 70-96% and 30-40% identities to plant and animal G protein α subunits, respectively, and 97.7% identity to each other. The regions essential for binding to GTP were preserved throughout all Gα subunits from higher plants and animals. However, the C-terminal amino acid sequences of TaGA1 and TaGA2 were similar to those of cereals Gα (rice and barley) but were different from the analogous sequences of mammals Gα subunits and also from those of the leguminous and solanaeceous Gα protein. Another cDNA clone, TaGB1 contained an open reading frame of 380 amino acid residues with mol. mass of 48.5 kDa. The predicted protein showed 70-89% identities to plant and over 50% to animal G-protein β subunits and preserved the most essential seven repeats for the WD-40 motif throughout the all plant and animal G protein β subunits. Southern analysis revealed that the hexaploid wheat genome contained at least three major copies of both Gα and Gβ genes with some minor homologous copies, suggesting that a small multigenic family is present for Gα and Gβ in the wheat genome. The mRNA for Gα in wheat showed tissue specific expression and the transcript levels of both TaGA1 and TaGA2 were abundant in one-week old seedlings, immature seeds of one week after anthesis, young spikes and internodes. However, spikes and internodes exhibited increased levels of mRNA accumulation, suggesting that the Gα is highly expressed in the actively elongating and fast growing tissues. Moreover, both TaGA1 and TaGA2 showed genome specific expression in wheat and may play a role in the light regulated growth and development of the seedlings. TaGB1 exhibited a synchronous pattern of expression profile to that of the Gα, except genome specific expression.