Epigenetic control of life cycle transitions in plants and beyond

Abstract:

The life cycle of most plants and algae alternates between two distinct life forms - a haploid gametophyte with a single copy of the genome and a diploid sporophyte with two. This so-called alternation of generations has profound evolutionary and ecological consequences, yet little is known about the control and origins of this developmental phenomenon. In flowering plants, the male gametophyte is highly reduced to just two cell types called the vegetative cell and sperm cells, which together make up the pollen grain. Our profiling of pollen chromatin in Arabidopsis has contributed to the understanding of how epigenetic reprogramming acts to specify each pollen cell type. In the vegetative cell, the reprogramming of DNA-H3K9 methylation facilitates pollen tube growth, while the reprogramming of H3K27me3 in sperm forecasts gene exp ression after fertilisation. I will discuss how these events help to rewire gene expression and ultimately drive the alternation of generations in Arabidopsis. I will then present our current efforts to develop a new model system to explore reproductive biology and life cycle control in red algae, the aquatic cousins of modern-day plants. Unique to most red algae is a highly complex alternation of three generations that underpins the success of this ancient and often inconspicuous group of organisms. This enigmatic tri-phasic life cycle, which arose independently from that of plants and green algae, provides a compelling case study into the origin, evolution and control of the alternation of generations, which will in turn provide new insights into the biology of an important but virtually unexplored group of eukaryotes.