Transcriptomics reveals the molecular mechanism underlying kiwifruit expansion following forchlorfenuron (CPPU) treatment

Kiwifruit is an economically and nutritionally valuable fruit. Forchlorfenuron (CPPU) is widely used to improve fruit set and yield of kiwifruit. However, the mechanism through which CPPU regulates fruit enlargement remains unclear. Physiological and RNA-seq data revealed that the greatest contribution of CPPU treatment to fruit growth occurred at 28 to 42 d after bloom (DAB). CPPU application accelerated sugar metabolism by increasing the content of sucrose through increasing the transcripts of genes such as SUSY, HK, and FK in sucrose metabolism. In the early stages of fruit development, up-regulation of the starch synthesis gene AGPase and the decomposition gene β-AMY indicated the occurrence of starch turnover. After CPPU treatment, genes related to the synthesis and signal transduction of auxin and gibberellins were down-regulated. During the early fruit developmental stage, the cytokinin content and the expression of signal transduction genes were increased. In addition, the expression of cyclin genes, related to cell division, was up-regulated within three weeks after CPPU treatment. This indicates that CPPU treatment promoted cell division during the fastest growth stage, which would lead to an increase in cell number and further increases in fruit size.