Cell-cell coordination in conjugatingChlamydomonas gametes

During conjugation, complementaryChlamydomonas gametes [mating type plus (mt+) and mating type minus (mt−)] are mutually attached via specific adhesion molecules, called agglutinins, which are located at the surface of the flagella. By these contacts the gametes are stimulated to fuse. It is demonstrated that fusion is preceded by a compulsary sequence of events: first, the flagellar swimming beat is arrested, next the flagellar contact is reinforced and finally, the position of the cell bodies is adjusted to permit fusion. Evidence is presented that each consecutive step of the mating process requires a higher level in cell-cell signalling, which is obtained by the formation of additional agglutinin contacts. It is shown that the mt+ and mt− traverse their conjugation process in synchrony, probably because the two sexes acquire new agglutinin contacts at equal rates. It is proposed that this symmetrical behavior is due to the complementarity of the mt+ and mt− agglutinin molecules. A scenario of the conjugation process inC. eugametos, incorporating the recent findings, is provided.