COS 168-2 - The role of host species differences in phylloplane pH regulation is shaping bacterial communities.

Abstract: Plants can differ in their ability to regulate pH conditions on their leaf surfaces (phylloplane), ranging from hyper-acidic carnivorous plants to hyper-alkaline Malvaceae. These physiological differences also extend to their ability to buffer against external pH changes (e.g., acid rain). Given the importance of soil pH to rhizosphere microbiota, phylloplane pH regulation may be important in shaping leaf microbiota, however, the potential consequences of this were previously unknown. In this study we took a metatranscriptomic approach to examine phylloplane bacteria on five plant species that differ in phylloplane regulation (including species of Nepenthes and Gossypium at the acidic and alkaline extremes, respectively). Young leaves were inoculated with a common microbial community sourced from a soil slurry. Leaves were also treated with one of two external pH treatments, pH 6.5 or pH 2. After exposure to the pH treatment, we sonicated the leaves to collect phylloplane microbes and performed total RNA extractions and sequencing. We assembled metatranscriptomes with SAMSA2. We found that host species significantly shaped community composition of microbial genes, which all diverged from the source inoculum; however this was not significantly impacted by pH treatment. Differential expression analysis, however, revealed differentially expressed genes between pH 2 and pH 6.5. Indicator genes analysis also revealed specific functional gene groups significantly associated with each plant species, underlining the importance of the active recruitment done by plant hosts in shaping their phylloplane microbiota.