Microbial interactions on plant leaves as a driver of local bacterial adaptation

• Applicants: Matthew Agler, Ph.D.; Professor Gianni Panagiotou, Ph.D.
• Subject Area: Organismic Interactions, Chemical Ecology and Microbiomes of Plant Systems
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 458884166

The leaves of Arabidopsis thaliana are colonized by diverse microbial communities composed of bacteria, fungi, and other eukaryotes. Bacteria in particular are common, diverse and occasionally abundant on leaves and as commensals, beneficials or highly adapted pathogens can tilt the balance between life and death. Leaf bacteria exhibit extensive genetic diversity at the strain level with clear consequences for how they interact with plants. It is generally assumed that this diversity arises from host selection, but we have observed that leaf fungi and other eukaryotes can drastically influence bacterial diversity, for example by manipulating host defenses. Whether and to what extent fungi can influence bacterial diversity in plant populations and the implications for hosts are unclear. We hypothesize that bacterial genetic diversity is shaped by both hosts and host-fungal interactions and aim to investigate this with combined experimental and bioinformatic approaches. First, we will use a metagenomics approach to study how bacterial strains and functions are distributed in nature in and between two A. thaliana populations with highly diverse leaf defense chemistry across 4 years and how this diversity correlates to fungal abundance. Next, we will examine diversity relevant for colonization of the two hosts by allowing hosts to select colonizers and use comparative genomics to understand host selection of traits. We will use the genomics data to investigate more precisely the role of selection by aliphatic glucosinolate-derived metabolites, a major A. thaliana leaf defense. Next, we will use gnotobiotic systems to look at diversity patterns relevant in the fungal-colonized host and how diversity and redundancy may dampen the host influence on interactions. Finally, we will use the systems to look at how traits important for tolerance to defense metabolites can be selected on by fungi. Together, this work will achieve one major advance in understanding – whether and how inter-kingdom interactions contribute to bacterial diversity in nature that is relevant for host health.

• DFG Programme: Research Grants