A3

Plants are colonized by a wide diversity of microbes including both eukaryotic and prokaryotic species. Only recently, metagenomic approaches have allowed exhaustive studies of the microbiota colonizing plant roots and above ground phyllosphere. Current research suggests that host genetics as well as a number of environmental factors are strong drivers of the phyllosphere and rhizosphere microbiota composition. So far, detailed studies have focused on the model plant species Arabidopsis thaliana. Only a few studies include experimental data of phyllosphere microbes, but these have presented evidence that the plant-associated microbiota may play a role in plant temperature and disease resistance.

Here we propose to investigate the phyllosphere microbiota of wild and domesticated wheat. A central question in our proposal is how plant domestication and cultivation has shaped the composition and genetic diversity of prokaryote and eukaryote microbes that are associated with the wheat phyllosphere. Based on studies of domesticated animals and plants, we hypothesize that domestication has decreased the diversity of microbial species and that the functional importance of phyllosphere- associated microbiota biodiversity likewise is decreased in domesticated wheat. In an evolutionary context we aim to characterize changes of the wheat microbiota over longer evolutionary times (wheat domestication and Triticum aestivum speciation, approx. 10-12,000 years ago) as well as across short evolutionary times (over 30 generations corresponding to 30 growing seasons). Our study will build upon unique collections of plant material at the center of origin of wheat, in the Near East including two wild wheat species Triticum dicoccoides and Aegilops speltoides and cultivated bread wheat Triticum aestivum. Fresh plant material will be collected not only with the purpose of extracting DNA for metagenome sequencing but also for the isolation of prokaryotic and eukaryotic symbionts (parasitic and commensals alike). Isolated and cultured organisms will be utilized for genome sequencing and functional genome analyses as well as for experimental work. In order to further investigate the stability and species specificity of microbiota associated with each wheat species we will use a synthetic phyllosphere community approach. The microbiota function will be investigated by combined inoculations of synthetic phyllosphere communities and a fungus that is pathogenic for wheat.

Our combined analysis of the prokaryotic and eukaryotic components of the wheat microbiota will serve as a first roadmap of wheat as a metaorganism, and is expected to provide novel insights into the diversity, evolution and function of the phyllosphere microbiota associated with this important crop metaorganism.