Molecular control of Arabidopsis male germline development by DAZ1 and DAZ2

Abstract

The male germline of flowering plants is a simple lineage of two cell types: generative (germ) cell and sperm cells. An asymmetric division of the microspore during pollen (male gametophyte) development produces the germ cell, which goes on to divide to form a pair of sperm that later fuse with egg and central cells at double fertilisation. The production of functional sperm cells depends upon cell cycle progression and cell specification, and three regulatory proteins – the MYB transcription factor DUO1, and the C2H2 zinc finger proteins DAZ1 and DAZ2 - acting in a gene network have been identified in Arabidopsis to be essential for both of these processes. Expression of DAZ1/DAZ2 is triggered by DUO1, and DAZ1/DAZ2 show functional redundancy. Understanding the mechanisms by which DAZ1 and DAZ2 control male germline development was a major aim of this thesis. The first objective was to explore sequence diversity among DAZ1/DAZ2 flowering plant homologues. This study established that the number of zinc finger domains differed between species, and mutating the zinc finger domains of DAZ1 had different effects on DAZ1 function. Functional analysis of DAZ1 EAR motifs showed that these sequences are important for in planta activity. DAZ1 and DAZ2 interact with the transcriptional co-repressor TPL, and a second objective was to investigate the spatiotemporal expression pattern of TPL and its family members in pollen, with male germline expression was observed for TPL and TPR2. The final objective was to identify genes under the regulation of DAZ1/DAZ2. While DAZ1 was predicted to be a transcriptional repressor, through transcriptomics it was revealed that a broad suite of genes were positively regulated by DAZ1, overlapping with targets of DUO1. The findings communicated in this thesis provide new insights into the molecular mechanisms controlling male germline development