Cell wall regeneration in Chlamydomonas: accumulation of mRNAs encoding cell wall hydroxyproline-rich glycoproteins.

The unicellular alga Chlamydomonas reinhardtii is surrounded by a cell wall composed entirely of hydroxyproline-rich glycoproteins (HRGPs). When the walls of vegetative cells are removed with the enzyme gamete autolysin (g-lysin), they regenerate a matrix within 3-4 hr. In vitro translation of mRNAs isolated from g-lysin-treated cells showed significant increases and decreases in abundance of several mRNAs encoding proline-rich polypeptides. Because the population of up-regulated mRNAs is likely to include species encoding cell wall components, expression of genes for two outer wall HRGPs (GP1 and GP2) was analyzed during wall regeneration by using cDNAs isolated from a C. reinhardtii lambda gt11 library. Transcripts encoding GP1 and GP2 were elevated severalfold within the first hour or regeneration, suggesting that upregulation of HRGP mRNAs is a primary response to cell wall removal by g-lysin. Cell wall regeneration in Chlamydomonas provides an accessible system to study HRGP gene expression during matrix development.