Genome-wide analysis of the MADS-box gene family in Sapindus mukorossi and functional characterization of SmAP1 and SmAP3 in flowering time and pistil development

The MADS-box gene family plays a pivotal role in regulating the transition from vegetative to reproductive growth, as well as flower, gametophyte, and fruit development. This study aimed to investigate the MADS-box gene family in Sapindus mukorossi . A total of 106 MADS-box genes were identified and classified into Type I (Mα, Mβ, Mγ) and Type II (17 subgroups). Comprehensive analyses included gene structure, conserved motifs, cis -regulatory elements, phylogeny, and protein interactions. Type I genes were primarily expressed in vegetative organs and during pericarp and seed development, whereas Type II genes were predominantly expressed in flowers, with expression varying across seven developmental stages in male and female flowers. Quantitative real-time PCR analysis revealed distinct temporal and spatial expression patterns of APETALA1 ( SmAP1 ) and APETALA3 ( SmAP3 ) during S. mukorossi flower development. SmAP1 expression peaked at the floral differentiation stage (FF4/MF4) and was highly enriched in both aborted and functional pistils, whereas SmAP3 reached maximum expression earlier, at the microsporocyte meiosis stage (FF2/MF2), with predominant accumulation in functional pistils. Functional validation through overexpression in Arabidopsis thaliana demonstrated that both SmAP1 and SmAP3 individually accelerated flowering and enhanced gynoecium development compared with wild-type plants, with SmAP1 showing a more pronounced effect. These results highlight the early and pistil-specific roles of SmAP1 and SmAP3 and provide a foundation for dissecting the molecular mechanisms controlling flowering and reproductive organ development in Sapindus species.