Effect of Cytochrome P450 on the Early Stage of Speciation
The selected and differentially expressed genes identified in the four groups of A. viridiflora were enriched in cytochrome P450 (ko00199, CYP450) (Figure S7). CYP450 is the largest family of enzyme proteins in plants and is involved in fatty acid metabolism, antioxidant biosynthesis, plant defense, secondary metabolite biosynthesis, hormone regulation and xenobiotic metabolism (Pandian, Sathishraj, Djanaguiraman, Prasad, & Jugulam, 2020). These pathways play a key role in the biosynthesis of secondary metabolites, antioxidants, and hormones in higher plants. In our study, the 11 genes enriched in CYP450 belong to eight subfamilies — CYP71, CYP76, CYP79, CYP81, CYP90, CYP98, CYP707, and CYP711. For example, CYP98 is located at a key position in the biosynthesis of phenylpropanoids, and the diversification of phenylpropanoids provides a driving force for the development and adaptation of terrestrial plants in new environments (A. Alber & Ehlting, 2012; A. V. Alber et al., 2019). ABA 8’-hydroxylase protein is encoded by the CYP707 gene and is the key step in ABA catabolism. It can regulate the ABA level, thereby regulating the physiological state of plants in response to environmental signals (Janda et al., 2021; Zheng, Huang, Xian, Wang, & Liao, 2012). Other subfamilies play a prominent role in the plant stress response (Irmisch, Zeltner, Handrick, Gershenzon, & Köllner, 2015; Johnson et al., 2014; M. Wang et al., 2020). Additionally, in response to environmental changes, the gene expression levels of these subfamilies have also changed accordingly (Baron, Schroeder, & Stasolla, 2012; Chan, 2012; Tao et al., 2017). Therefore, the differentiation of the CYP450 superfamily may have driven the speciation of A. viridiflora , and its diversification provides a genetic basis to adapt to different environments. Because the CYP450 superfamily is widely present in angiosperms, its important role in the early speciation of angiosperms warrants further exploration.