Format: ORAL

Yuling Yue1,2, Anna Neubauer1,2, Gaurav Sablok3, Jaakko Hyvnen3, Pe´ter Szo¨ve´nyi1,2

1Department of Systematic and Evolutionary botany, University of Zurich, Switzerland 2Zurich-Basel Plant Science Center, Zurich, Switzerland  3Faculty of Biological and Environmental Science, University of Helsinki, Helsinki, Finland 

It was proposed that the molecular network enabling and controlling intimate plant-microbe symbiotic interactions could have evolved from a general starvation response. Molecules released during starvation by the host plants could have been recruited by microbes to recognize the plant host and the ancestral starvation network of the host plant could have been extended with components enabling proper control of the symbiotic interaction. Nevertheless, this hypothesis remains largely untested because information on the consequences of nutrient starvation is mainly available for vascular plants but missing for most non-vascular plant lineages. Here we investigated this hypothesis by exploring gene expression changes during nitrogen starvation in the two major lineages of bryopyhtes, hornworts and liverworts, capable of establishing intimate symbiotic interaction with cyanobacteria. By conducting comparative analyses with symbiotic and non-symbiotic vascular as well as non-vascular plants we found that the global gene expression response to nitrogen starvation is highly conserved across bryophytes and vascular plants. Furthermore, we observed little difference in response to nitrogen starvation in symbiotic and non-symbiotic species and between species establishing symbiosis with AM fungi, nodule forming bacteria or cyanobacteria. These observations suggest that the nitrogen and general nutrient starvation response is highly conserved across the two major lineages of land plants the vascular plants and the bryophytes and likely represents a starvation response inherited from their common ancestor. While the overall starvation response was conserved, we were also able to identify pathways and molecule groups only induced in the cyanobacteria-hosting bryophyte species implying their potentially role in attracting the symbionts in the initial phase of the symbiosis. Overall, our results are in line with the proposed hypothesis and suggest that regulatory gene networks governing the intimate symbiotic interaction between plants and microbes have likely evolved from a conserved starvation response involving few regulatory changes.