Fig. 8
A model for DUO1 evolution during green plant evolution. DUO1 arose from a pre-existing MYB TF in an ancestor of stoneworts by acquiring a DUO1-type feature in region B of its MYB domain (A.1). DUO1 innovation in ancestral plants promoted a specific program of differentiation of male gametes. Before the emergence of land plants, the sperm lineage-specific expression of DUO1 was acquired (B.1) and a change in region C occurred to refine DNA-binding specificity (B.2), which has been conserved among land plants. The DUO1 C-terminal domain also underwent large changes, presumably adapting its transcription activation function for individual species during evolution (B.3). In conjugating green algae, the DUO1 ortholog is no longer expressed in the sperm lineage (C.1) and has accumulated mutations in the MYB domain (C.2), resulting in a loss of DUO1 function. During land plant evolution, the DUO1 C-terminal activation domain has been modified, establishing lineage-specific activity (D.1). In seed plants, DUO1 retained its DNA-binding specificity and other male gamete-related genes, such as those important for fertilization, were recruited to (D.2) and motility-related genes were removed from (D.3) the set of genes controlled by DUO1, leading to significant rewiring of the DUO1 regulatory network. Modes of sexual reproduction are shown on the left37. Sexual reproduction is unknown in Mesostigma, and Klebsormidium. Note that some gymnosperms (Ginkgo and cycads) have flagellate sperm cells delivered by a pollen tube
