Relevant Degree Programs
Our work aims to explore evolutionary potential of microalgae using Chlamydomonas reinhardtii as a model system. 1) Functional genomics projects to improve photosynthetic productivity of microalgae under stressors like excess light and poor nutrient. 2) Molecular genetics projects to analyze mutants defective for sexual development in Chlamydomonas reinhardtii. 3) Comparative genomics projects to decipher the key developmental mechanisms that enabled the emergence of land plants from their green algal ancestors.
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Graduate Student Supervision
Doctoral Student Supervision (Jan 2008 - May 2021)
The full abstract for this thesis is available in the body of the thesis, and will be available when the embargo expires.
Master's Student Supervision (2010 - 2020)
A fundamental aspect of plant survival is the development of a resilient cell wall. Throughout the life cycle of the unicellular alga Chlamydomonas reinhardtii, the cell wall is continuously synthesized and remodelled. When cells are starved of nitrogen, they differentiate into gametes and enter the sexual (meiotic) phase. In doing this, mating gamete cells shed their cell walls via gametolysin, fuse their naked protoplasts, and build an exceptionally hardy zygote cell wall. Previous research on the sexual life cycle has focused on regulatory events upstream of the mating reaction, i.e. gametogenesis, and downstream of cell fusion during zygote development. As such, we don’t yet understand how cells are responding to wall shedding at the onset of the mating reaction. A recent transcriptome analysis has reported a set of genes that are specifically regulated by gametolysin-mediated wall shedding, consisting of two major functional categories – protein processing-related and cell wall-related. The research presented here attempts to understand the level at which these genes are regulated and establishes three hypotheses for what the ‘trigger’ of their regulation might be. Using a suite of target genes as representative factors of the gametolysin-mediated event, we performed promoter-reporter and mRNA expression analyses in several treatment conditions and cell lines to examine this regulation. We found both target genes and their respective promoters are strongly induced by gametolysin, indicating transcription-level regulation. When cells were pre-treated with a protein synthesis inhibitor prior to gametolysin, we observed differential effects on the transcription of our target genes, suggesting multiple regulatory proteins control this event. We also observed that an ER stress response likely helps to regulate cell wall recovery, as a stress response-impaired mutant showed diminished transcript expression following gametolysin treatment. Cell wall-defective mutants were found to have a negligible response to gametolysin, but expressed our target genes constitutively, indicating the need for cells to maintain a cell wall. Early investigations of our hypotheses for the ‘trigger’ of the gametolysin-mediated response suggests a minor role for osmotic stress signalling and that sensing the condition of the cell wall is likely the primary ‘trigger.’
The emergence of embryophytes from their charophyte-like ancestor is estimated to have occurred 476-432 MYA. During the adaptation to land, embryophytes evolved to have sporic meiosis; whereas charophyte algae undergo zygotic meiosis. The transition to land required the embryophytes to develop specialized tissues and a cuticle to survive drier terrestrial environments. This transition resulted in increasing elaboration of the body plan in the diploid phase, establishing the sporophyte. It is hypothesized that diversification of heterodimeric TALE homeobox genes in the ancestral charophyte algae may have acted as new types of master regulators to control diploid-specific developmental program, which initiated the development of novel sporophytic body plan. This study is focused on determining TALE homeobox genealogy by comparing genetic sequences and gene structure of TALE homeobox found in the transcriptomes of Picocystis salinarum (prasinophyte), Mougeotia sp. (charophyte). and Cosmocladium constrictum (charophyte). The interaction of TALE homeobox proteins from Picocystis salinarum was tested with a Y2H assay. Prior to this study, it was known that the diploid developmental program was regulated by KNOX and BELL classes of TALE homeobox genes in embryophytes and KNOX and GSP1 classes of TALE homeobox genes in Chlamydomonas reinhardtii (chlorophyte). Through phylogenetic analysis, I found that charophytes express KNOX, BELL and GSP1 classes, and P. salinarum expresses KNOX, GSP1, divergent TALE, and two red algal homologs of the TALE homeobox. Furthermore, comparison of intron location indicated that the BELL and GSP1 genes in the charophytes may be homologous. Intron comparisons and phylogenetic analysis of the KNOX genes indicate that KNOX II class from streptophyta and KNOX from chlorophyta share the greatest similarity, whereas KNOX I class can be hypothesized to have emerged by gene duplication in the early charophyte ancestor. The Y2H assay of TALE homeobox from Picocystis salinarum shows that GSP1 and KNOX can interact, whereas the possibility of an interaction with the red algal homolog is inconclusive.