Grape is a globally significant fruit-bearing crop, and the grape flower bud differentiation essential to fruit production is closely related to light quality. To investigate the regulatory mechanism of grape flower bud differentiation under red‒blue light, the transcriptome and hormone content were determined at four stages of flower bud differentiation. The levels of indole-3-acetic acid (IAA) and abscisic acid (ABA) in grape flower buds at all stages of differentiation under red‒blue light were higher than those in the control. However, the levels of cytokinins (CKs) and gibberellic acid (giberellins, GAs) fluctuated continuously over the course of flower bud differentiation. Moreover, many differentially expressed genes were involved in auxin, CK, GA, and the ABA signal transduction pathways. There were significant differences in the AUX/IAA, SAUR, A-RR, and ABF gene expression levels between the red‒blue light treatment and the control buds, especially in regard to the ABF genes, the expression levels of which were completely different between the two groups. The expression of GBF4 and AI5L2 in the control was always low, while the expression under red‒blue light increased. AI5L7 and AI5L5 expression levels showed an upwards trend in the control plant buds and gradually decreased in red‒blue light treatment plant buds. Through weighted gene coexpression network analysis, we determined that the transcription factors WRK48 (WRKY family), EF110 (ERF family), ABR1, CAMTA3 (CAMTA family), and HSFA3 (HSF family) may be involved in the regulation of the GBF4 gene. This study lays a foundation for further analysis of grape flower bud differentiation regulation under red‒blue light.

Grape is a globally significant fruit in the world. Flower bud differentiation of grape is closely related to light quality. In order to understand the regulation mechanism of grape flower bud differentiation under red-blue combined light, the transcriptome and hormone content were determined in four stages of flower bud differentiation. The contents of IAA and ABA in grape buds at all stages of flower bud differentiation under red-blue combined light were higher than those in control. However, the contents of CKs and GAs fluctuated continuously during the process. Moreover, it was found that many differential expression genes (DEGs) were involved in auxin, cytokinin, gibberellin, and the abscisic acid signal transduction pathway. There were significant differences in the genes of AUX/IAA, SAUR, A-RR, and ABF between the red-blue combination light treatment and the control buds, especially the ABF genes were utterly different. The expression of GBF4 and AI5L2 in control were always low, while the expression under the red-blue combined light increased. AI5L7 and AI5L5 showed an upward trend in control and gradually decreased under the red-blue combined light. Through weighted gene co-expression network analysis (WGCNA), transcription factors WRKY family WRK48, ERF family EF110, ABR1, CAMTA family CAMTA3, HSF family HSFA3 may be involved in the regulation of the GBF4 gene. This study will lay a foundation for further analysis of grape flower bud differentiation regulation under red-blue combined light.