Expression Patterns, Activities and Sugar Metabolism Regulation of Sucrose Phosphate Synthase, Sucrose Synthase, Neutral Invertase and Soluble Acid Invertase in Different Goji Cultivars during Fruit Development

Abstract Sugars are crucial factors that contribute to fruit flavor. To uncover the regulatory mechanism of sugar metabolism in developing fruit, we isolated four genes, encoding key enzymes (sucrose phosphate synthase (SPS—EC 2.3.1.14), sucrose synthase (SuSy—EC 2.4.1.13), neutral invertase (NI—EC 3.2.1.26) and soluble acid invertase (SAI—EC 3.2.1.26), related to sugar metabolism in Goji (Lycium barbarum L.) fruit and examined sugar content, gene expression and enzyme activities in developing fruit of two cultivars. The results showed that Ningqi No. 1 maintained high levels of hexose (glucose and fructose) and lower sucrose than Ningqi No. 3. Expression levels of SPS and NI were demonstrated to be tied to corresponding enzyme activities while SAI and SuSy were not connected to changes in enzyme activities during fruit development in either cultivar. In this sense, NI and SPS seem to play a major role in sugar metabolism. These findings suggested that cultivar Ningqi No 1. has enhanced hexose synthesis and hydrolysis of sucrose relative to Ningqi No. 3. This work demonstrated a novel function profile of sugar metabolism as well as relevant gene expression to explain how different sugar levels in different Goji cultivar fruits are maintained during fruit development.