Induction of collective behavior by β-1,3-glucans in microalgae.

Abstract

β-1,3-glucans are multifaceted molecules, playing a key role in aquatic ecosystems where they store atmospheric CO₂, as well as in human health, where they help fight pathogens and have anticancer properties. Until now, no role other than sugar storage had been attributed to β-1,3-glucans in algae. We show here that in <i>Chlamydomonas reinhardtii</i>, β-1,3-glucans control aggregation, a collective behavior in response to stress. We have identified the enzymes specifically involved in β-1,3-glucan synthesis and degradation during aggregation. The transcriptome of β-1,3-glucan-induced aggregation revealed an early effect of this elicitor. A comparative genomic analysis allowed us to envisage a potential role for β-1,3-glucans in the transition to multicellularity in Volvocales. The finding of the function of β-1,3-glucans in the stress response of the unicellular model organism <i>Chlamydomonas</i> sheds light into their mode of action. This is particularly relevant given their potential roles combatting pathogenic fungi in plants and animals.