Overexpression of a loquat (Eriobotrya japonica Lindl.) vacuolar invertase affects sucrose levels and growth

Sucrose and its cleavage products are essential molecules in higher plants. Vacuolar invertase (VIN) is a type of invertase that is specifically localised in the vacuole. It irreversibly cleaves sucrose into glucose and fructose, and plays important roles in sugar accumulation or cell expansion. In this study, a full-length cDNA of the VIN gene, EjVIN, was isolated from loquat (Eriobotrya japonica Lindl.). The EjVIN encoding protein possesses typical and highly conserved motifs among plant VINs, including the beta-fructosidase motif (NDPNG), catalytic domain (WECVD) and a possible vacuolar targeting motif (ILPN). Phylogenic analyses showed that EjVIN is close to apple and pear VIN, falling within the VIN subgroup. EjVIN transcript and acid invertase activity were highest in the early stages of fruit development and in mature fruit. The transcript of EjVIN was significantly enhanced in vivo after 3 h of treatment with fructose or glucose. The transgenic tobacco plants overexpressed EjVIN grew faster with decreased size. Further analyses indicate that the sucrose levels were decreased, but fructose levels were slightly increased in immature transgenic plants compared with wild type plants. The results indicate that EjVIN play more important role during early loquat fruit development stage. Overexpression of loquat EjVIN accelerated sucrose hydrolysis, affected plant growth, which possibly due to a modification of the metabolic fluxes in the transgenic plants at early development stage.