AGPS and BAM genes dramatically improve ‘Ganlv 1′ (Actinidia eriantha) fruit quality through starch metabolism during fruit development

Abstract

In previous field investigations, we found that Actinidia eriantha has sweeter flavor than other kiwifruit, which provided an opportunity to explore the formation mechanism of sweet flavor. In this study, we selected three cultivars of kiwifruit with different accumulation characters of starch and sugar, i.e., ‘Ganlv 1′ (A. eriantha), ‘Jinkui’ (A. chinensis var. deliciosa), and ‘Jinyan’ (A. eriantha × A. chinensis var. chinensis), as materials to identify the key regulatory enzymes and genes. Our results showed that the maximum starch content in A. eriantha was the highest. Importantly, the A. eriantha also had the highest degradation rate, because of the highest amylase activity in A. eriantha among the cultivars tested. Fifty-nine differentially expressed genes involved in starch metabolism were identified by the transcriptome data, the accuracy of transcriptome data was verified by qRT-PCR analysis. Among these genes, starch synthesis related genes were significantly up-regulated at 120 DAFB in A. eriantha, including AGPS1.1, AGPS1.2 and WAXY1. And key degradation related genes were also identified, such as BAM3.2, BAM3.3, PHO1, PHO2.2, SUS2.1 and SUS2.2. Moreover, transient transformations provided overexpressing AcBAM3.3 in kiwifruit could up-regulate the expression of AcBAM3.3 gene and degrade starch content by 15.1∼22.3 %. In conclusion, the stronger biosynthesis capacity and the faster inversion rate of starch in the fruit of A. eriantha were the reasons for its higher sweet flavor in which benefit to fruit quality.