Evolution and control of the DUO1 regulatory network in land plants

The sexual reproduction of land plants depends on the successful production and union of male and female gametes. The production of functional sperm cells involves the control of germ cell division and differentiation. These factors are dependent upon a key regulatory module formed by the MYB transcription factor DUO1 POLLEN 1 (DUO1), and DUO1-ACTIVATED ZINC FINGER 1 / DUO1-ACTIVATED ZINC FINGER 2 (DAZ1/DAZ2), C2H2 zinc finger proteins. The major aim of this thesis is to further understand the DUO1 network in land plants. The work is aligned as two separate strands, one in angiosperms and the other in bryophytes. DAZ3 and its homolog, DAZ3L, are direct target genes of DUO1. The evolution and potential function of DAZ3 and DAZ3L in Arabidopsis sperm cell development was investigated. Phylogenetic analysis showed that DAZ3 and DAZ3L are restricted to the eudicots superrosid-superasterid clade and most likely evolved from ancestral DAZ1 sequences. The analysis of Arabidopsis knockout mutants showed that neither DAZ3 nor DAZ3L have essential functions in sperm cell development, fertilisation or seed development. The function of DUO1 in the model bryophyte Physcomitrella patens (moss) was also investigated. The absence of DUO1 in moss was shown to prevent the differentiation of spermatogenous cells. This resulted in a lack of flagella, rendering spermatogenous cells immotile, hence knockout mutants lacking DUO1 function were infertile. The potential conservation of the DUO1-DAZ1 network in moss was also analysed based on in silico analysis of expression data and the presence of DUO1 binding sites (DBS). The similarity in transcript profiles between PpDUO1 and PpDAZ1 in maturing antheridia and the presence of DUO1 binding sites in the PpDAZ1 upstream region indicate that PpDAZ1 is a direct target of PpDUO1. Hence, it is plausible that the wider DUO1-DAZ1 network is conserved in bryophytes.