| Summary: | Conservative gene families in plants, which are closely related to innovations in flowering plants, have long and complex evolutionary histories. Here, we used the <i>SQUAMOSA</i> promoter-binding protein (SBP-box) gene family as an example to study conservative gene families in flowering plants. In total, 11 groups, including nine angiosperm-conservative groups and two monocot- and eudicot-specific groups, were identified. Among the nine angiosperm-conservative groups, four are conserved in all land plants and the remaining five are angiosperm-specific. The five angiosperm-specific groups exhibit structural and functional diversity and evolved together, along with the evolution of flowering plants. The expansion of <i>SBP</i> genes was affected by miR156, and the miR156-regulated <i>SBP</i> genes tend to retain more copies. Our results reflect the dynamic evolutionary process of the different groups, with the identification of two genetic lines via synteny analyses. In addition, miR156 showed a close evolutionary relationship with <i>SBP</i> genes, suggesting that it may originate from face-to-face tandem duplication of <i>SBP</i> genes. <i>SBP</i> genes without an miR156 binding locus are usually functionally conservative or housekeeping like, belonging to the terrestrial-conservative group. In contrast, <i>SBP</i> genes with miR156 binding sites are selected by angiosperms to regulate more complex physiological processes.
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