Metatranscriptomic response of the wheat holobiont to decreasing soil water content

It is admitted that multicellular hosts and their microbiota form an indissociable unit, the holobiont. Even though it is posited that this unit would react in a coordinated fashion to environmental stress, the role of each of the partners is ill-defined. Here, we subjected wheat to a gradient of water availability in the field using rainout shelters that let through 100%, 75%, 50% and 25% of the precipitation. At the height of the growing season, we sampled plant roots and rhizosphere, and extracted and sequenced their RNA. We more specifically compared the 100% to the 25% treatments using differential abundance analysis. In the roots, the majority of the differentially abundant (DA) transcripts belonged to the fungi, and most were overexpressed in the 25% precipitation treatment. Approximately 10% of the DA transcripts belonged to the plant, and most were underexpressed in the 25% precipitation treatment. In the rhizosphere, most of the DA transcripts belonged to the bacteria and were mostly overexpressed in the 25% precipitation treatment. Taken together, our results are showing that the response of the wheat holobiont to decreasing precipitation levels is mostly carried out by fungi and bacteria, with very little response from the plant itself.