The sex-inducing pheromone of the multicellular green alga Volvox carteri is a glycoprotein that triggers development of males and females at a concentration Ͻ 10 ؊ 16 M. By differential screening of a cDNA library, two novel genes were identified that are transcribed under the control of this pheromone. Unexpectedly, one gene product was characterized as a lysozyme/chitinase, and the other gene product was shown to encode a polypeptide with a striking modular composition. This polypeptide has a cysteine protease domain separated by an extensin-like module from three repeats of a chitin binding domain. In higher plants, similar protein families are known to play an important role in defense against fungi. Indeed, we found that the same set of genes triggered by the sexual pheromone was also inducible in V. carteri by wounding. INTRODUCTIONThe sex-inducing pheromone (sex inducer) of the multicellular green alga Volvox carteri is a glycoprotein that is probably among the most potent biological effector molecules known. At a concentration of Ͻ 10 Ϫ 16 M, the pheromone converts asexually growing males and females to the sexual pathway, producing in the next generation sperm-and eggcontaining organisms, respectively (Starr and Jaenicke, 1974;Tschochner et al., 1987;Mages et al., 1988).The asexually growing organism of V. carteri is composed of only two cell types exhibiting a complete division of labor: 2000 to 4000 biflagellate Chlamydomonas -like somatic cells are arranged in a monolayer at the surface of a hollow sphere (Starr, 1969(Starr, , 1970, and 16 much larger reproductive cells ("gonidia") lie just below the somatic cell sheet. Eleven or 12 rapid and synchronous cleavage divisions of a gonidium generate all of the cells of an adult organism. Volvox cells are surrounded and held together by a glycoproteinrich extracellular matrix (ECM) (for review, see Sumper and Hallmann, 1998).Many lines of evidence indicate that the ECM plays a key role in the sexual induction process. The earliest biochemical responses to the pheromone detected thus far are structural modifications within the ECM Sumper, 1982, 1986;Gilles et al., 1983). In particular, the volvocacean ECM contains members of the newly described pherophorin family (Sumper et al., 1993;Godl et al., 1995Godl et al., , 1997. Pherophorins are glycoproteins that contain a C-terminal domain with homology to the sex-inducing pheromone. Some pherophorins are incorporated into the ECM constitutively, but under the influence of the pheromone, synthesis of other members of the pherophorin family is initiated, and from a subset of pherophorins (pherophorin II), this pheromone-like domain becomes proteolytically liberated from the parent glycoproteins. It has been proposed that this modification and processing of the ECM are part of the signal amplification process required to achieve the exquisite sensitivity observed for this sexual induction system. A molecular-genetic approach was initiated to detect additional genes that might be induced under the influence of t...

The DNA sequet, ce coding for the sexual inducer glycoprotein of Volvox carteri and its N-terminal signal I~ptide was placed under the control of the repressible acid phosphatase promoter of the yeast Saccharomyces cerevisiae in a yeast--E, coil shuttle vector. Yeast transformed by this construct synthesized and mecreled into the culture medium biologically active inducer in amou~lts two to three orders of magnitude higher than observed in the Volvox system.