Associate Professor Lynette Brownfield

Research

Plant sexual reproduction

Like in animals, sexual reproduction in flowering plants relies upon the production of male (sperm) and female (eggs) gametes and their fusion upon fertilization. Despite the importance of plant fertility for seed production and agricultural productivity, relatively little is known about the molecular processes underlying gamete development and function. Work in my lab is focused on using genetic and molecular approaches to understand key stages of male gametophyte (pollen) and sperm cell development.

Plant male meiosis and the formation of unreduced gametes

Polyploidy, the presence of more than two sets of chromosomes, has had a major impact upon the evolution of plants and the development of modern agricultural crop varieties. The major mechanism of polyploid formation is believed to be through the production of gametes that have not had their ploidy level reduced during meiosis and are thus termed unreduced. We use a mutant, called jason, in the model plant Arabidopsis thaliana to investigate how unreduced gametes form.

We have found that cytoplasmic organisation is essential in preventing unreduced male gamete formation. In particular, a band of organelle that forms across the middle of meiotic cells during the second division is important as it provides a physical barrier to keep the two meiotic spindles separated. We are now investigating how the molecular function of the JASON protein to determine how it impacts upon cytoplasmic organisation.

Specification of the male germ line in Arabidopsis

In flowering plants the male germ line is not formed until late in development when a haploid microspore undergoes a highly asymmetric division. This forms a large vegetative cell and a smaller germ cell, which represents the start of the male germ line. During germ-line development the germ cells is engulfed within the cytoplasm of the vegetative cell where it expresses the proteins required for sperm cell function and undergoes a single mitotic division. We are interested in how the asymmetric division specifies the male germ line, largely by investigating the regulation of the key germ-line transcription factor DUO1.

Positions

Enquires about projects from prospective graduate students and postdoctoral fellows are welcome. Information about scholarships for New Zealand postgraduate students go to the University of Otago website:.

Postgraduate and scholarship awards

Awards

Ben Peters

2016, Department of Biochemistry Best Student Paper, 1st place

For the paper: A cis-regulatory module in the transcription factor DUO1 promoter. Benjamin Peters, Jonathan Casey, Jack Aidley, Stuart Zohrab, Michael Borg, David Twell, and Lynette Brownfield., Plant Physiol 2016 p. pp.01192.2016. Published:16 November 2016 Abstract: The development of the male germline within pollen relies upon the activation of numerous target genes by the transcription factor DUO POLLEN1 (DUO1). The expression of DUO1 is restricted to the male germline and is first detected shortly after the asymmetric division that segregates the germ cell lineage. Transcriptional regulation is critical in controlling DUO1 expression since transcriptional and translational fusions show similar expression patterns. Here we identify key promoter sequences required for the germline-specific regulation of DUO1 transcription. Combining promoter deletion analyses with phylogenetic footprinting in eudicots and in Arabidopsis accessions, we identify a cis-regulatory module, Regulatory region of DUO1 (ROD1), which replicates the expression pattern of DUO1 in Arabidopsis thaliana. We show that ROD1 from the legume Medicago truncatula directs male germline-specific expression in A. thaliana, demonstrating conservation of DUO1 regulation among eudicots. ROD1 contains several short conserved cis-regulatory elements, including three copies of the motif DNGTGGV, required for germline expression and tandem repeats of the motif YAACYGY, which enhance DUO1 transcription in a positive feedback loop. We conclude that a cis-regulatory module conserved in eudicots, directs the spatial and temporal expression of the transcription factor DUO1 to specify male germline fate and sperm cell differentiation.

Ben Peters

2015, New Zealand Society of Plant Biologists Best Student Presentation at ComBio, 1st place