Abstract

Cucumber (Cucumis sativus L.) is a Cucurbitaceae plant that often suffers from fruit drop and deformity caused by excessive fruiting, poor growth, and unfavorable environmental conditions during cultivation.Forchlorfenuron [N-(2-chloro-4-pyridyl)-N'-phenylurea (CPPU)] is a plant growth regulator that has been widely used in the production of cucumbers and other horticultural plants because of its significant effects in promoting fruit set and enlargement. However, the underlying mechanism through which CPPU regulates cucumber fruit development remains unclear. To verify the role of CPPU in regulating cucumber fruit development, field experiments were conducted in both spring and autumn. The results confirmed that CPPU application significantly promoted fruit enlargement, shortened the time from flowering to harvest of marketable fruits, reduced fruit curvature, and increased the marketable fruit rate. Interestingly, we found that environmental conditions influence the regulatory effect of CPPU on fruit expansion. To investigate the molecular basis underlying CPPU-mediated regulation of fruit development, transcriptome analysis was performed. Firstly, 44 cross-stage differentially expressed genes (DEGs) were identified through differential gene analysis. Subsequent Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) functional annotation revealed that plant hormone signaling pathways are the key pathways mediating CPPU-regulated fruit expansion. Furthermore, five key candidate genes (CsaWIP2, CsPILS7, CsJOX2, CsGIR1, and CsAAA18193) responding to the CPPU signal were screened and preliminarily validated using machine learning and real-time quantitative polymerase chain reaction techniques. This study clarified CPPU's effect on cucumber fruit development, and the selected genes provided theoretical support for molecular breeding of cucumber and high-quality, high-yield cultivation optimization.