The Sex-Inducing Pheromone and Wounding Trigger the Same Set of Genes in the Multicellular Green Alga Volvox

Abstract

The sex-inducing pheromone of the multicellular green alga Volvox carteri is a glycoprotein that triggers development of males and females at a concentration <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.

Response to the Sexual Pheromone and Wounding in the Green Alga Volvox: Induction of an Extracellular Glycoprotein Consisting Almost Exclusively of Hydroxyproline

“…Wounding Induces Transcription of dz-hrgp Gene-As demonstrated recently (18), all genes known so far to be under the control of the sex-inducing pheromone are also triggered by wounding. This observation led us to investigate whether transcription of dz-hrgp gene is also responsive to wounding.…”

“…Surprisingly, the simple multicellular green alga Volvox responds to wounding in much the same way as observed in higher plants. As was demonstrated recently (18), Volvox responds to wounding with the synthesis of a chitinase as well as a protease that is combined with chitin-binding modules. With the additional demonstration of a typical HRGP that is produced in response to wounding, it now appears that much of the response scenario found in higher plants already exists in multicellular green algae.…”

“…RNA samples isolated 3, 6, and 12 h after the application of the pheromone were pooled, and a cDNA library (ZAP) was constructed from the corresponding poly(A) ϩ mRNA preparation. Repeated differential screenings of the cDNA library with cDNA derived from asexual versus sexually induced organisms resulted in the detection of novel clones in addition to the already known members of the pherophorin family (15)(16)(17) and to the chitinase and the cysteine protease described recently (18). One of these novel clones was named dz-hrgp for reasons explained below.…”

“…By differential screening of a cDNA library, additional genes were recently identified that are transcribed under the control of the sex-inducing pheromone (18). Unexpectedly, genes were found, in addition to those encoding the pherophorins, that encode extracellular chitinases and proteinases.…”

Insect feeding mobilizes a unique plant defense protease that disrupts the peritrophic matrix of caterpillars

“…The effect of this unique sequence on protease function is currently unknown. In addition, the amino acid sequence from position 188 to 236 has approximately 70% similarity to the chitin-binding domains present in a Volvox cysteine protease (11), wheat germ agglutinin (12,13), and hevein (14,15), and recent experiments confirmed that the 33-kDa cysteine protease has chitin-binding activity (unpublished data). mir1 has been mapped to chromosome 6 (bin 6.02) on the maize genome, where there is a significant quantitative trait locus for resistance to European corn borer leaf feeding (16).…”