Comprehensive genome-wide characterization of the MIKC-type MADS-box family members and the dynamic expression profiling throughout the development of floral buds in Populus tomentosa

Poplar is a major silvicultural tree species for industrial production, with versatile applications in construction, furniture, pulp and biofuel. The phenotypic appearance of male or female floral buds in poplar trees, exhibits a strikingly similar morphology at corresponding developmental stages. However, there are significant differences in internal anatomical structures. The MIKC-type MADS-box transcription factor family plays an indispensable role in regulating the development of floral organs and increasing vegetative biomass, and it is also of great significance in elucidation of the aforementioned morphological differences. This study systematically analyzed the MIKC-type MADS-box transcription factor family in Populus tomentosa. A total of 100 MIKC-type MADS-box genes were identified, which were divided into 14 subfamilies. We examined the physicochemical properties, gene structure, conserved motifs, chromosome distribution, collinearity, promoter cis-acting elements, gene expression profiles, and protein-protein interaction network of these 100 MIKC-type MADS-box members. Excitingly, four clusters of PtMADS members exhibited a high level of abundant expression in the initial and mature floral buds of both male and female, suggesting critical significance in tuning the morphogenesis and development of floral organs, as well as in the modulation of reproductive fitness. The protein-protein interaction network diagram corroborated these findings, substantiating the speculated roles of these genes. Our findings lay a foundational framework for future functional explorations and potential applications of MIKC-type MADS-box genes in this industry tree species.