Genomic basis of multiphase evolution driving divergent selection of zinc-finger homeodomain genes

Gene families divergently evolve and become adapted as different genes with specific structures and functions in living organisms. We performed comprehensive structural and functional analyses of Zinc-finger homeodomain genes (ZF-HDs), including Mini zinc-finger genes (MIFs) and Zinc-finger with homeodomain genes (ZHDs), displaying competitive functions each other. Intensive annotation updates for 90 plant genomes verified that most MIFs (MIF-Is) exhibited distinct motif compositions from ZHDs, although some MIFs (MIF-Zs) contained ZHD-specific motifs. Phylogenetic analyses suggested that MIF-Zs and ZHDs originated from the same ancestral gene, whereas MIF-Is emerged from a distinct progenitor. We used a gene-editing system to identify a novel function of MIF-Is in rice: regulating the surface material patterns in anthers and pollen through transcriptional regulation by interacting ZHDs. Kingdom-wide investigations determined that (i) ancestral MIFs diverged into MIF-Is and MIF-Zs in the last universal common ancestor, (ii) integration of HD into the C-terminal of MIF-Zs created ZHDs after emergence of green plants and (iii) MIF-Is and ZHDs subsequently expanded independently into specific plant lineages, with additional formation of MIF-Zs from ZHDs. Our comprehensive analysis provides genomic evidence for multiphase evolution driving divergent selection of ZF-HDs.