Genome-Wide Characterization of the GRAS Gene Family in Cyclocarya paliurus and Its Involvement in Heterodichogamy

The GRAS gene family, derived from GAI, RGA, and SCR, plays a crucial role in plant growth and development. In the diploid Cyclocarya paliurus (2n = 2x = 32) with heterodichogamous characteristics, 51 CpGRAS genes were identified and phylogenetically classified into 10 subfamilies. Structural analysis revealed that CpGRAS genes possessed a canonical GRAS domain, but 70% lacked introns. WGD/segmental duplication was the major driver in the expansion of the CpGRAS family. In addition, a Ka/Ks ratio below 1 for these genes implied functional constraints and evolutionary conservation. Transcriptional profiling revealed significant differential expressions of CpGRAS genes between male and female flowers from two mating types, protogyny (PG) and protandry (PA). Notably, members of the DELLA subfamily exhibited significant upregulation in female flowers at the inflorescence elongation (S3) stage. The expression level of CpSCL6-2 in late-flowering samples (PA-F and PG-M) was higher than in early-flowering ones (PA-M and PG-F). Co-expression analysis identified that CpRGL1 and CpGAI-2 of the DELLA subfamily, along with CpSCL6-2, acted as hub genes, implying their crucial roles in floral development and potential involvement in the heterodichogamous flowering mechanism in C. paliurus. These findings broaden our understanding of CpGRAS genes and provide new insights into the molecular basis of heterodichogamy.