Abstract
Kiwifruit (Actinidia chinensis) is a rich nutritious fruit crop owing to a markedly higher content of vitamin C and minerals. To promote fruit set and to increase the yield of kiwifruit, forchlorfenuron (CPPU) has been widely applied. However, the molecular details regarding CPPU controlling kiwifruit development, especially at the fastest fruit growth stage, remain unknown. In the present study, we measured the effect of CPPU on developmental regulation in red-fleshed kiwifruit (Actinidia chinensis ‘Hongyang’). Additionally, a cytological analysis was performed to clarify the precise changes in the cell structure of the CPPU-treated kiwifruits. Moreover, the concentration of endogenous phytohormones, including indoleacetic acid (IAA), zeatin (ZT), gibberellic acid 3 (GA3), and abscisic acid (ABA), were measured by Enzyme-linked Immunosorbent Assay (ELISA). Furthermore, RNA-Seq was performed to dissect the complicated molecular mechanisms, with a focus on biosynthesis, metabolism, and signaling compounds, such as endogenous hormones, sugars, and L-ascorbic acid. Our results demonstrated that CPPU treatment not only regulates the size and weight of a single fruit but also improves the quality in ‘Hongyang’ kiwifruit through the accumulation of both soluble sugar and vitamin C. It was also seen that CPPU regulates kiwifruit development by enhancing cell expansion of epidermal cells and parenchyma cells, while, promoting cell division of subepidermal cells. Additionally, CPPU significantly increased the gibberellin and cytokinin biosynthetic pathway and signaling, while repressing auxin and ABA biosynthetic pathway; thus, signaling plays an essential role in CPPU controlling kiwifruit development. Notably, transcriptomic analysis revealed that a total of 2244 genes, including 352 unannotated genes, were differentially expressed in kiwifruits because of CPPU treatment, including 127 transcription factors. These genes are mainly enriched in plant hormone signal transduction, photosynthesis, MAPK signaling pathway, starch and sucrose metabolism, and phenylpropanoid biosynthesis. Overall, our results highlight that CPPU regulation of kiwifruit development is mainly associated with an antagonistic and/or synergistic regulatory role of endogenous phytohormones, and enhancing the energy supply. This provides new insights into the molecular details of CPPU controlling kiwifruit development at the fastest fruit growth stage, which is of agricultural importance for kiwifruit breeding and crop improvement.
Highlights
After fertilization, the main contributors to fruit development are cell division and cell expansion, which are tightly regulated by genotypes and environmental conditions [1,2,3,4]
We found that 5 mg L-1 of CPPU treatment strongly increased both fresh weight and fruit size of single fruit (S1 Fig), and the effect was enhanced with a treatment concentration from 5 to 20 mg L-1 of CPPU (S1 Fig)
These results suggest that a dose-dependent CPPU regulatory model exists in A. chinensis ‘Hongyang’, and 20 mg L-1 of CPPU was the optimal concentration (Fig 1A)
Summary
The main contributors to fruit development are cell division and cell expansion, which are tightly regulated by genotypes and environmental conditions [1,2,3,4]. Plant hormones play a dominant role in cell proliferation and cell expansion, auxins (IAAs), gibberellic acids (GAs), and cytokinins (CTKs), which participate in controlling the growth of related tissues and determine the fruit size [8, 9]. The Fw2.2 gene encoding plant-specific and fruit-specific protein, functions in regulating fruit size in tomato [15]. 4 genes with high expression levels in the early stages of fruit development were discovered in kiwifruit; these genes encode the homologs of plant metallothionein-like protein, β-subunit of mitochondrial ATP synthase, and two unknown proteins [17]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
