Two tunicamycin-sensitive components involved in agglutination and fusion ofChlamydomonas reinhardtii gametes

Abstract

To find out glycoproteins involved in the mating reaction ofChlamydomonas reinhardtii, the effect of tunicamycin (TM), a potent inhibitor of glycosylation of proteins, was studied. TM, when present during gametogenesis, blocked the acquisition of agglutinability ofmt + cells. TM also inhibited the recovery of agglutinability ofmt + gamete after trypsin treatment. On the contrary, TM blocked neither the acquisition of agglutination during gametogenesis ofmt - cells nor the recovery of their agglutinability after trypsinization. It was found, however, that the TM-treatedmt - gametes can agglutinate but do not fuse with non treatedmt + gametes at all. When gametes of gam-1mt -, a conditional mutant strain for cell fusion, were induced at non permissive temperature of 35°C and then transferred to 25°C, the ability of cell fusion was acquired after about 5 h incubation. Presence of TM completely blocked this acquisition. Based on these evidence, we conclude that at least two TM-sensitive glycoproteins are included in the mating reaction. The first component is located on the flagellar surface ofmt + gamete and responsible for agglutination withmt - flagella. The second component occurs on the surface ofmt - gamete and plays a role in the fusion withmt + gamete.