Characterization of transgenic rice plants that express rgp1 the gene for a small GTP-binding protein from rice

The rgp1 gene, which encodes a small GTP-binding protein fi om rice, was introduced into rice protoplasts by electroporation. Transformed protoplasts were cultured on liquid protoplast-culture medium for 1 month, and then cells that had proliferated were transferred to a selection medium that contained 50 mg/l hygromycin B. Among 50 colonies that were selected and transferred to regeneration medium, 3 colonies generated shoots. However, two of the three shoots failed to form roots and ceased growing. A single regenerated shoot that formed roots was planted in soil and transferred to a greenhouse. Southern hybridization showed that the regenerated plant harbored a single copy of the introduced gene. The transformant (T(0)) plant was shorter than the controls, it developed three times as many tillers as controls, it developed three times as many tillers as control plants but it produced mostly sterile seeds. In a test of hygromycin resistances, viable seeds segregated into resistant and sensitive seedings at a ratio of approximately 1:3. The progeny (T(1)) plants were short with many tillers, and some produced seeds normally. The T(2) seedlings grew more rapidly than control seedlings for the first 28 days after germination, but control plants subsequently outgrew the T(2) plants. Northern blotting analysis revealed that the rgp1 gene in T(2) plants was expressed consitutively throughout all developmental stages. The results suggest that the observed phenotypic changes were due to expression of the exogenous rgp1 gene.