Tomato Plants Ectopically Expressing Arabidopsis GRF9 Show Enhanced Root Development and Improved Fruit Production in Field

Agronomic performance of transgenic tomato over-expressing functional gene was rarely investigated in field. In an attempt to improve low phosphate (P) stress tolerance of tomato (Solanum lycopersicum) plants and promote tomato fruit production in field, an expression vector containing an Arabidopsis 14-3-3 protein, General Regulatory Factor 9 (GRF9) cDNA driven by a cauliflower mosaic virus 35S promoter was transferred into tomato plants. Transgenic expression of GRF9 was proved by quantitative real-time PCR analyses. The degree of low P tolerant transgenic plants was found to be significantly greater than that of wild-type tomato plants as measured by root development, P concentration under hydroponic system. For the transgenic tomato, roots had higher uptake of P, as evidenced by tissues P concentrations and relative expression of the genes LePT1 and LePT2 in both normal and low P hydroponic solutions. GRF9 over-expressing plants had much enhanced proton exudation and activity of plasma membrane H⁺-ATPase (PM H⁺-ATPase) in the roots under low P hydroponic conditions. Thus, besides enhanced root development, higher phosphate transporters genes expression and strengthened acidification in the vicinity of the roots may be the important mechanisms for transgenic tomato plants to acquire P in soil. Subsequent field trail of tomato fruit production at two P levels indicated that GRF9 could improve tomato total production and may play an interesting role in early fruit maturity. These results suggested that the heterologous Arabidopsis GRF9 gene can confer P deficit resistance in transgenic tomato plants and promote fruit production.