Comparative transcriptomics reveals hormone signaling and MADS-box genes in divergent development of inflorescences...

Hormone signaling and MADS-box genes regulate grapevine tendril and inflorescence growth divergence, offering molecular insights for managing tendril growth. Grapevine (Vitis vinifera L.) tendrils and inflorescences are homologous organs; however, their divergent development has important agronomic consequences because excessive tendril growth increases vineyard management costs. To explore the regulatory mechanisms, we compared the inflorescence-prone cultivar 'Einset Seedless' (ENT) with the tendril-prone cultivar 'Pinot Noir' (PN) using anatomical observation, transcriptome analysis of specific tendril nodes, and functional characterization of MADS-box genes. ENT exhibited a higher flowering rate at tendril nodes 1-4 than PN. Transcriptome profiling of specific tendril nodes uncovered 549 differentially expressed genes (DEGs) through an intersection/exclusion strategy, with Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment indicating that hormone and mitogen-activated protein kinase (MAPK) signaling were the primary candidates driving the divergence. To assess the spatiotemporal dynamics of these DEGs, we performed Mfuzz clustering, which revealed that multiple expression trajectories were highly consistent with the flowering gradient across different ENT and PN nodes. Plant hormone signal transduction was the predominantly enriched pathway across all dynamic clusters, highlighting the centrality of phytohormones in this process. Guided by this transcriptional evidence, we measured endogenous zeatin and gibberellin (GA₃) contents in the nodal tissues. Remarkably, the zeatin-to-GA₃ ratio not only paralleled the flowering gradient but also correlated with the cluster expression trajectories, providing physiological evidence for a cytokinin-gibberellin interaction model governing organ divergence. Additionally, we analyzed the differentially expressed transcription factors among the DEGs and identified a MADS-box gene, FRUITFULL-LIKE (VvFUL-L), which was markedly upregulated in PN tendrils. Heterologous overexpression of VvFUL-L in arabidopsis promoted early flowering and reduced inflorescence branching, suggesting its potential role in regulating lateral meristem development and affecting tendril formation. Collectively, these findings establish that Hormone Signaling, particularly cytokinin-GA crosstalk, and MADS-box regulators, such as VvFUL-L, are key regulators of inflorescence versus tendril growth in grapevines, providing a basis for future molecular and breeding studies.