Transcriptomic and Proteomic Insights into Low Red Light: Far-Red Light Ratios Induced Internode Elongation in Cucumber Seedlings

The ratio of red to far-red (FR) light (the R/FR ratio) is a core signal regulating shade-induced internode elongation in plants, but the underlying mechanism in cucumber remains not fully elucidated. Therefore, in the present study, cucumber (Cucumis sativus L. ‘Zhongnong No. 26′) was used as the material, and through a combination of physiological, transcriptomic, and proteomic analyses, we investigated the mechanism underlying internode elongation via R/FR ratio in cucumber plants. Low R/FR ratio significantly promoted cucumber seedling internode elongation by enhancing the longitudinal growth of internode cells. Hormonal profiling decreased the contents of indole-3-acetic acid (IAA), salicylic acid (SA), cytokinin (CTK; tZR, T-zeatin, and iPR), and ethylene (Eth), whereas jasmonic acid (JA) and gibberellin (GA) contents were elevated in cucumber seedling internodes. Bioinformatics analysis revealed that low R/FR ratio upregulated GA biosynthesis-related genes (KAO, GA20ox), and the expression of genes/proteins encoding cell wall remodeling/biosynthesis enzymes (EXP, XTH and CesA), and aquaporin proteins (AQPs). Exogenous GA4/7 mimicked the promotive effect of low R/FR on internode elongation under white light, while the GA biosynthesis inhibitor paclobutrazol (PAC) reversed this response, confirming a central role for GA in this process. These results reveal the crucial role of cell wall biosynthesis and hormone metabolism-related genes/proteins in low R/FR ratio-induced cucumber internode elongation. Such work may further elucidate the evolutionary and agronomic trade-offs associated with shade avoidance and provide a basis for optimizing canopy architecture and light management in cucumber cultivation.