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