Transcriptome analysis reveals the roles of chlorophyll a/b-binding proteins (CABs) and stay-green (SGR) in chlorophyll degradation during fruit development in kiwifruit

Abstract

ABSTRACT Commercial cultivars of kiwifruit (Actinidia spp.) can have green-fleshed or yellow-fleshed fruit depending on their chlorophyll degradation ability. In recent years, an increasing number of yellow-fleshed cultivars have been bred in China. However, the mechanisms underlying the flesh colouration of these new cultivars remain elusive. In this study, the pigment contents of the yellow-fleshed cultivar ‘Jinshi NO.1’ were determined during fruit development, and RNA sequencing was conducted to screen for differentially expressed genes and identify potential candidates for pigment metabolism. The chlorophyll content continuously decreased from 0 days after full bloom (DAFB) (T1) to 189 DAFB (T4), resulting in a more than 30-fold change, while the contents of anthocyanins and carotenoids showed sharp decreases from T1 to 44 DAFB (T2) and remained stable thereafter. Weighted gene co-expression network analysis (WGCNA) indicated that the chlorophyll contents were highly correlated with chlorophyll-degradation-related genes, especially three chlorophyll a/b-binding protein (CAB) genes and one stay-green gene (AcSGR1), but no carotenoid-related genes. Furthermore, these genes were found to be highly correlated with 15 transcription factors and 11 hub genes. These results indicate the important role of chlorophyll degradation in the colouration of ‘Jinshi NO.1’ and provide candidates for further functional characterisation and transcriptional regulation.