Mating-Induced Shedding of Cell Walls, Removal of Walls from Vegetative Cells, and Osmotic Stress Induce Presumed Cell Wall Genes in Chlamydomonas

Abstract

The first step in sexual differentiation of the unicellular green alga Chlamydomonas reinhardtii is the formation of gametes. Three genes, GAS28, GAS30, and GAS31, encoding Hyp-rich glycoproteins that presumably are cell wall constituents, are expressed in the late phase of gametogenesis. These genes, in addition, are activated by zygote formation and cell wall removal and by the application of osmotic stress. The induction by zygote formation could be traced to cell wall shedding prior to gamete fusion since it was seen in mutants defective in cell fusion. However, it was absent in mutants defective in the initial steps of mating, i.e. in flagellar agglutination and in accumulation of adenosine 3#,5#-cyclic monophosphate in response to this agglutination. Induction of the three GAS genes was also observed when cultures were exposed to hypoosmotic or hyperosmotic stress. To address the question whether the induction seen upon cell wall removal from both gametes and vegetative cells was elicited by osmotic stress, cell wall removal was performed under isosmotic conditions. Also under such conditions an activation of the genes was observed, suggesting that the signaling pathway(s) is (are) activated by wall removal itself.

Stress induces the assembly of RNA granules in the chloroplast of Chlamydomonas reinhardtii

“…The conditions of heat shock, osmotic shock, and phosphate deprivation were described previously ( von Gromoff et al, 1989 ;Hoffmann and Beck, 2005 ;Moseley et al, 2006 ). For the condition shown in Fig.…”

Uniparental inheritance of cpDNA and the genetic control of sexual differentiation in Chlamydomonas reinhardtii

“…The zygote-specific genes that are involved in this process are ZSP1 (Woessner and Goodenough 1989) and ZSP2 (Suzuki et al 2000). Other HRGPs (GAS28, 30) and glycoproteins (GAS31) are expressed in the late phase of gametogenesis and are further up-regulated in zygotes (Hoffmann and Beck 2005). Kubo et al (2008) identified candidate zygotic genes that may be related to cell wall synthesis thorough sugar metabolism (EZY4: UDP-glucose 4-epimerase like protein, EZY11: UDP-glucose protein: protein trans glycosylase, EZY12: UDP-glucose 6-dehydrogenase, EZY16: cell wall protein pherophorin-C15).…”

Gene Regulatory Networks for the Haploid-to-Diploid Transition of Chlamydomonas reinhardtii

“…It has long been known that if the supernatant from mating cells is harvested and applied to vegetative cells or unmated gametes, their walls are also removed and the cells proceed to assemble new walls via activating genes encoding wall proteins and proteins of unknown functions (Hoffmann and Beck, 2005;Kubo et al, 2008;Ning et al, 2013). The walls of vegetative and gametic cells are apparently identical (defined as the VG-wall in contrast to the zygotic wall [Z-wall]; Monk, 1988).…”

“…Vegetative cells shed the so-called mother cell wall after their mitotic progeny have formed their own cell walls, and upon encountering a gamete of the opposite mating type, gametes must be able to rapidly shed their walls to allow cell fusion. In both vegetative cells and gametes, transcripts for cell wall genes are up-regulated when their walls are experimentally released by incubating cells in g-lysin (Hoffmann and Beck, 2005;Kurvari, 1997). One notable difference is that only the vegetative wall needs to support large increases in cell volume, which requires continuous remodeling of the existing wall layers.…”