A Comparative Study Of Brachypodium Transcriptome In Three Arbuscular Mycorrhizal Symbioses

Arbuscular mycorrhizal (AM) symbiosis is a partnership between plants and fungi, in which the plant trades carbon for mineral nutrients from the fungus. All proposed biofeedstocks are able to form AM symbioses, and therefore have the potential to benefit from the phosphorus, nitrogen, and other elements supplied by the fungus. The resultant increase in plant biomass can therefore be achieved in a more sustainable way, by reducing the need for phosphorus-based fertilizers, which are obtained from non-renewable sources.

To elucidate the molecular mechanisms of the AM-induced plant biomass increase, we developed an experimental system in grass Brachypodium distachyon – a model organism for biofuels and biofeedstocks. Transcriptomes from three Brachypodium-AM symbioses that differ in their ability to increase shoot biomass were profiled using Illumina HiSeq. Shoot and root mRNA was sequenced in treatments with and without each of the three fungal symbionts, at two key developmental time points. This resulted in an extensive and well-replicated set of gene expression data.

Substantial differences in differentially expressed genes were mapped across the three symbioses. Among them are enzymes participating in abscidic acid biosynthesis and nitrate assimilation pathways, consistent with the effects of AM symbiosis on plant morphology, biomass increase and drought tolerance. We also report the discovery of a number of novel plant transcription factors, likely having regulatory functions in the establishment of symbiosis. Finally, our annotation reveals a number of AM-induced plant genes with the expected symbiosis-related functions, such as cell wall degrading enzymes, and transporters of phosphate, ammonium and sugars.