Induced defence of red algae against pathogens

We investigate the alga/pathogen interaction in the system of the red alga Chondrus crispus (left on top) and the green algal pathogen Acrochaete operculata (below left), which is able to grow within the tissue of the red algal host. This process, called endophytism, can be inhibited during certain developmental phases of C. crispus. During the resistant, gametophytic, phase of the life cycle, C. crispus can recognise the attacker and kill it by an immediate release of hydrogen peroxide. We found that carrageenans from the red alga induce the release of asparagine from the green algal parasite. The free amino acid itself acts as a substrate for an amino acid oxidase of the host that releases micromolar amounts of hydrogen peroxide, sufficient to contain the attacker. The aim of a related collaborative project (European Union EPIFIGHT) is to understand the biological bases of the interactions between the red alga Gracilaria chilensis and its main epiphytic pests. We are elucidating the defensive chemistry of the host with special emphasis on the induction of reactions upon pathogen stress. Both, the signals and hormones involved in the up-regulation of the production of defensive metabolites are investigated using analytical chemical and biochemical approaches.