Response to the sexual pheromone and wounding in the green alga Volvox: Induction of an extracellular glycoprotein consisting almost exclusively of hydroxyproline

The extracellular matrix (ECM) of Volvox is modified during development or in response to external stimuli, like the sex-inducing pheromone. It has re cently been demonstrated that a number of genes triggered by the sex-induci ng pheromone are also inducible by wounding. By differential screening of a cDNA library, a novel gene was identified that is transcribed in response to the pheromone. Its gene product was characterized as an ECM glycoprotein with a striking feature: it exhibits a hydroxyproline content of 68% and t herefore is an extreme member of the family of hydroxyproline-rich glycopro teins (HRGPs), HRGPs are known as constituents of higher plant ECMs and see m to function as structural barriers in defense responses. The Volvox HRGP is also found to be inducible by wounding. This indicates that the wound re sponse scenarios of higher plants and multicellular green algae may be evol utionary related.