Evolution of Plant Male Germline-Specific Transcription Factor DUO POLLEN 1

Flowering plants account for the 30 crops that provide 95 % of the food for humans. The reproduction of this group depends on the production of two twin sperms. The establishment of the male germline lineage requires the transcription factor DUO POLLEN 1 (DUO1). DUO1 is required for both the cell cycle progression and sperm cell differentiation. This thesis focused on the origin of DUO1 and its target regulation. Much work was dedicated in searching the evolutionary origin of DUO1 in the R2R3 MYB clade. Based on the analysis of sequences homologous to DUO1 and its sister clade GAMYB, the earliest DUO1 homolog was identified in the green algae. The DUO1 clade did not proliferate after multiple polyploidy events, possibly restricted by its male germline-specific role supported by transcriptome data. The ancestral DUO1 experienced a major MYB domain sequence change in the bryophytes and a second change in the C-terminus in the angiosperms. The MYB domain changes caused a change in the target DNA sequence, which has then been conserved among Embryophyta DUO1 homologs. Another change also happened in the region where a miR159 binding site is present in most angiosperm DUO1 homologs. Sequence and functional analysis showed that this change evolved long before the emergence of miR159. The changes in the C-terminus of DUO1 led to a higher target promoter activation capability in the angiosperm homologs, which was confirmed by functional tests of the angiosperm and bryophyte DUO1. This C-terminal region contains the transactivation domain (TAD) of DUO1 and certain functionally important motifs were highlighted in the study. While these motifs indicated that DUO1 was a member of a TAD family, it was also demonstrated that unknown sequences carry critical features for activation. Together these results mapped the evolution history of DUO1 in the Streptophyta lineage.