Project (Sophie de Vries)

Genome biology of a perpetual symbiosis and evolution of the symbiotic network

Symbiotic interactions are key to life. Two major symbiotic events changed life on earth fundamentally. These are the origin of the mitochondrion and the origin of the chloroplast. Among land plants the water fern Azolla stands out: it harbors a vertically inherited cyanobacterial symbiont. The symbiont has some features that have it resemble an organelle. Indeed, it shows genome reduction and is obligate to the fern. What is more, survival of the fern in natural habitats is dependent on the survival and function of the symbiont. There is no Azolla species or ecotype known to date that does not harbor the symbiont, nor can the symbiont be re-recruited upon loss. The genus Azolla has undergone an ancient whole-genome duplication event at its origin. The genome subsequently evolved into a diploidized paleopolyploid. This begs the question whether and how genome evolution in Azolla is linked to the establishment of its permanent symbiosis. To address this, we aim to assemble chromosome-scale genomes of two Azolla species from distinct taxonomic groups using Hi-C and ONT long-read sequencing and identify the two subgenomes and haplotypes of each species and elucidate the symbiont-dependent and -independent evolution of genome architecture. We will further profile and manipulate symbiosis development and profile transcriptomic responses. From this we will establish a comprehensive symbiont responsive network in different Azolla species. Using the subgenome- and haplotype-resolved data we will test whether and how the genomic components contribute differently to the establishment and maintenance of the Azolla symbiosis.