Genome-wide identification of MADS-box gene family members in poplar and functional characterization of PagMADS23a in the regulation of stomatal density

MADS-box family genes act as key regulators of plant growth, hormone signal transduction and secondary metabolism regulation. In this study, 150 MADS-box genes were identified in 84 K poplar ( Populus alba × P. glandulosa ). The phylogeny, gene structure, conserved motifs, collinearity, and cis-acting elements of these genes were analyzed, and the PagMADS-box genes were clustered into 17 groups. The results indicated that their evolution may be regulated by domain and motif distributions and influenced by multiple segmental and tandem duplication events. Meanwhile, based on differential gene expression analysis between tetraploid and diploid poplars, the PagMADS23a gene was identified and found to be significantly downregulated in the apical buds of tetraploid poplars, and its protein was localized to the nucleus. Transgenic analysis showed that overexpression of PagMADS23a increased stomatal density and promoted vegetative growth but reduced drought tolerance, whereas RNAi lines displayed opposite phenotypes. RT-qPCR results revealed that PagMADS23a markedly affected the expression of stomatal development–related genes, including EPF1, EPF2, EPFL9, SDD1, TMM, SPCH, MUTE, and FAMA. This study systematically characterized the 84 K poplar MADS-box transcription factor family, revealing the role of PagMADS23a in stomatal density regulation and providing insights into the drought resistance mechanisms of woody plants. • 150 MADS-box genes were identified in 84 K poplar, which were divided into 17 groups. • PagMADS23a was downregulated in tetraploid 84 K poplar and localized in the nucleus. • Overexpression of PagMADS23a increases plant stomatal density. • PagMADS23a affects growth and drought resistance by regulating stomatal density.