Overexpression of RrGGP2 and RrDHAR Increases Ascorbic Acid Content in Tomato

Abstract

Ascorbic acid (AsA) is the most abundant antioxidant in plants and is an important nutritional index for agricultural products. Some plants, such as Rosa roxburghii Tratt., contain exceptionally high levels of AsA, but are relatively unpalatable. In view of its role in human health, as well as plant growth and development, we examined the effects of two important AsA regulatory genes from R. roxburghii in tomato, with the aim of producing a crop of higher nutritional quality. RrGGP2 and RrDHAR were cloned from R. roxburghii fruit. The overexpression vectors were made using 35S promoters and mediated by Agrobacterium tumefaciens to obtain the overexpression lines. A PCR and qRT-PCR verified that the two genes had been inserted and overexpressed in the tomato leaves and fruits. The results showed that the overexpression of RrGGP2 increased tomato leaf and fruit AsA content by 108.5% and 294.3%, respectively, while the overexpression of RrDHAR increased tomato leaf and fruit AsA content by 183.9% and 179.9%. The overexpression of RrGGP2 and RrDHAR further changed the expression of genes related to AsA metabolism, and the upregulation of one such gene, SlGGP, may have contributed greatly to the increase in AsA. Results here indicate that RrGGP2 contributes more towards fruit AsA accumulation in tomato than RrDHAR.