Secondary metabolites that shape the permanent symbioses between Azolla ferns and nitrogen-fixing cyanobacteria

Abstract

Azolla has various applications such as green fertilizer, substrate for potting soil, animal feed or even human consumption. The high protein content and growth speed combined with the independence on agricultural land and nitrogen fertilizer, give it strong potential as sustainable protein crop to replace imported soy. Being the only obligate plant-cyanobacteria symbiosis it is furthermore an interesting study subject for fundamental research. Here we first focus on the chemistry, biosynthesis and spatial distribution of Azolla specialized metabolites that determine the usability of Azolla biomass and protein. We then research how secondary metabolism changes by environmental cues typical for the Netherlands such as a cold winter. We further focus on the biotic interaction between the crane fly Nephrotoma cornicina and Azolla, which share the same wetland habitat. A specialized metabolite from this insect overrules the coordinate differentiation of Nostoc azollae and therefore is of particular interest to reveal how the fern host might control the life cycle of the cyanobacteria. This essential mechanism has not been researched before. Finally, we explore Azolla transformation because of its importance to reveal gene function and the associated molecular mechanisms.