Evolutionary Conservation and Regulatory Diversification of AS1 Homologs in Soybean

The establishment of dorsoventral polarity is a critical step in leaf morphogenesis, enabling the transition from radial primordia to flattened laminae. The MYB domain transcription factor ASYMMETRIC LEAVES1 (AS1) plays a central role in this process by regulating leaf polarity and developmental transitions, primarily through the repression of Class I KNOX genes. Here, four AS1 paralogs were identified in soybean (Glycine max), two of which showed collinearity with Arabidopsis thaliana and Medicago truncatula. The AS1 proteins of soybean and Arabidopsis exhibit high conservation, whereas the four GmAS1 genes in soybean display different tissue-specific expression patterns. Strikingly, each GmAS1 gene was able to fully rescue the defective phenotype of the Arabidopsis as1 mutant, indicating that GmAS1 genes are functionally conserved in leaf polarity regulation. Promoter analysis further indicated that GmAS1 genes are enriched in cis-acting elements related to light response, hormone regulation, development, and stress response, suggesting potential subfunctionalization among these paralogs. In conclusion, these findings demonstrate that GmAS1 genes are evolutionarily conserved in function but potentially diversified in regulation, providing new insights into their role in leaf polarity and stress adaptation.