Genome-Wide Identification and Expression Analysis of the PEBP Gene Family in Cymbidium sinense Reveals CsFTL3 as a Floral Inhibitor

TL;DR

This study identifies a gene in the orchid Cymbidium sinense that delays flowering, offering insights into its regulation and potential for breeding.

Contribution

The study identifies CsFTL3 as a novel floral repressor gene in Cymbidium sinense with unique regulatory features.

Findings

CsFTL3 is a floral inhibitor that delays flowering when overexpressed in Arabidopsis.

CsFTL3 contains amino acid substitutions that distinguish it from typical flowering promoters.

CsFTL3 expression is regulated by gibberellin, abscisic acid, and low temperature.

Abstract

This study comprehensively characterizes the PEBP gene family in Cymbidium sinense, an orchid with a prolonged vegetative phase that limits its industrial production. Genome-wide analysis identified six CsPEBPs, classified into FT-like, TFL1-like, and MFT-like subfamilies. Evolutionary, gene structure, and collinearity analyses revealed both conservation and lineage-specific diversification of these genes. CsFTL3, a distinctive FT-like member, displayed notably high expression during the bud undifferentiated stage, followed by a sharp downregulation upon floral initiation. Functional studies identified CsFTL3 as a key floral repressor. Heterologous overexpression in Arabidopsis delayed flowering time from 32.0 days (wild-type) to 63.0–75.3 days (transgenic) and increased rosette leaf number from 12.6 to 33.0–34.5, while its knockdown via virus-induced gene silencing (VIGS) in C. sinense accelerated floral bud development and upregulated flowering-promoter genes. Phylogenetically, CsFTL3 falls within the flowering repressor FT-I clade, and multiple sequence alignment identified critical amino acid substitutions (Y134S, W138L, Q140E) that likely underpin its functional divergence from typical flowering promoters. Furthermore, promoter analysis revealed an enrichment of light-, hormone-, and stress-responsive cis-elements, and its expression was modulated by gibberellin (GA), abscisic acid (ABA), and low-temperature treatments. Predicted protein–protein interaction and transcriptional regulatory networks provide preliminary insights into its complex regulation. We conclude that CsFTL3 acts as a crucial floral inhibitor, integrating environmental and endogenous cues to repress flowering. These findings offer fundamental insights into the molecular mechanisms of flowering in orchids and provide a valuable genetic resource for molecular breeding programs aimed at achieving precise flowering time control.

Figures