Over-expression of GhDWF4 gene improved tomato fruit quality and accelerated fruit ripening

Brassinosteroids（BRs）, a class of steroidal phytohormones are essential for many biological processes in plant. However, little is known about their roles in fruit development. Tomato is a highly valuable vegetable and has been adopted as the model species for studying fruit growth, development, and ripening. To understand the role of endogenous BRs in the development of tomato fruit, the expression patterns of three homologues of DWF4 gene were investigated and the transgenic tomato plants were generated in which the Gh DWF4 gene from upland cotton（Gossypium hirsutum L.） was ectopically expressed. The contents of main quality components were analyzed in fruits of transgenic tomato line and non-transgenic line（control plant, CP） when the fruit was mature. Sl CYP90B3 that possesses high homology with Gh DWF4 preferentially expressed in mature fruit. Significantly higher contents of soluble sugar, soluble proteins, and vitamin C were obtained in fruit of transgenic tomato lines compared with those in the CP. Furthermore, overexpressing Gh DWF4 promoted fruit growth and ripening. The weight per fruit was increased by about 23% in transgenic lines. In addition, overexpressing Gh DWF4 promoted the germination of transgenic tomato seeds and hypocotyl elongation of seedlings. These results indicated that overexpressing Gh DWF4 gene in tomato could increase the contents of many nutrients in fruit and accelerate fruit ripening. It is suggested that increased endogenous BRs in fruit affect the growth and development of tomato fruit and therefore improved the nutrient quality of tomato.