Growth Regulating Transcription Factors and Massilia bacteria in Plant Microbiome Feedbacks

MSc Sam Field

10/2023

Supervision: Dr. Henry Janse van Rensburg, Prof. Klaus Schlaeppi

Abstract:

Plants, like other living organisms, need to control their microbiome to encourage beneficial symbiotic interactions and dissuade pathogenic interactions. This is often done via root exudates; compounds such as primary and secondary metabolites that are secreted through the root. One such class of exudated secondary metabolite, Benzoxazinoids (BXs), have been shown to impact the rhizobiome of Arabidopsis thaliana (Arabidopsis) and subsequently modify the plant’s growth patterns, increasing its growth on soil that was conditioned by growing BX producing plants on the soil before growing Arabidopsis, thereby modifying the soil microbiome. It is hypothesised that the microbiome induced upregulation of Growth Regulation Factors (GRFs), a class of plant transcription factors (TFs), is linked to better growth. Here, we tested genetically the involvement of GRFs in Arabidopsis’ growth increase seen on BX+ conditioned soil as well as attempt to isolate a key microbe previously correlated to the growth promotion seen on BX+ conditioned soils, a Massillia bacterium. Findings suggest that GRF3 and GRF1 play roles in the response to BX+ conditioned soils, although the observed response was not as hypothesized, with wild type Arabidopsis plants growing smaller on BX+ conditioned soils than BX- conditioned soils. Out of 316 screened isolates, 3 isolates were identified to be of the Massilia genus, however none mapped accurately to the specific bacterium that was being searched for. These isolates were however identified to be of genera commonly associated with plant growth promoting bacteria (PGPB) and may provide a useful resource for further plant microbe research. This research indicates that GRFs are likely implicated in Benzoxazinoid feedbacks in Arabidopsis, although further research is required for verification. No conclusion can be made on the influence of the specific Massilia bacterium that was searched for, as it was not isolated.