Changes in gene expression patterns during the sexual life cycle of Chlamydomonas reinhardtii

Abstract

In the sexual life cycle of Chlamydomonas reinhardtii, three types of cells can be distinguished: vegetative cells, gametes, and zygotes. Using is vivo pulse labelling of proteins with 35S-sulfate, followed by two-dimensional separation of the polypeptides on polyacrylamide gels, we analyzed the patterns of protein synthesis typical for each cell type. Approximately 20% of the proteins detected were synthesized at very different rates when the pattern from vegetative cells was compared to that of gametes or zygotes. Gamete formation from vegetative cells is a two-step process controlled by two extrinsic signals: first, nitrogen-starvation induces the differentiation of vegetative cells to pregaroetes, which are then competent for a light–induced differentiation to mature gametes. The majority of the changes in rate of synthesis of different proteins during the switch from vegetative cells to gametes was observed already in pregametes. Between the stages of pregametes and gametes, changes in the rates of synthesis of four proteins were detected. Induction of zygote germination resulted in complex changes in the patterns of gene expression. Evidence is presented for three groups of proteins whose synthesis is turned on or turned off during zygote germination.