Understanding soil microbiome feedbacks on growth and defence of Arabidopsis thaliana

MSc Viola D’Adda

03/2024

Supervision: Katja Stengele, Prof. Klaus Schlaeppi

Abstract:

Plants and soil microorganisms live in close association and influence each other: plants release metabolites into the soil to select beneficial microorganisms that, in turn, can affect plant fitness. Maize and other cereals are distinguished by the presence of benzoxazinoids (BX) in their exudates, whose derivative microbiome is known to influence the growth and pathogen resistance of a second plant generation. In the case of Arabidopsis thaliana there is evidence that soil conditioned with wild type maize, and therefore rich in BX (BXp soil), induces increased rosette size, increased rosette resistance to the pathogenic fungus Botrytis cinerea, and, in general, an upregulation of several genes related to induced defence, stress response, and biosynthesis of functional small RNAs.

However, this latter aspect needs confirmation, and it is precisely to investigate the role of induced defence and small RNAs on BX-mediated A. thaliana’s increased growth and defence that this work was performed. For this, we cultivated A. thaliana on BXp soil and, as a control, on BXm soil, i.e. soil poor in BX since conditioned with the bx1 mutant maize, defective in BX synthesis. We than compared the rosettes size as well as the susceptibility of the plants to the pathogens B. cinerea and Pseudomonas syringae pathovar tomato DC3000 LUX. Furthermore, we studied the dependence of BX-induced growth and defence feedbacks on different soil samples from the same field.

The results of this work show that the effect of BX on the growth and defence of A. thaliana is not consistent, but can vary from positive, to neutral, to negative depending on soil origin. In addition, we could demonstrate the importance of small RNAs in the establishment of growth feedback. Thus, BX may indeed be relevant in improving the growth and defence of a second generation of plants, but in a soil origin-dependent manner. By finding out also on which soil characteristics these positive feedbacks depend, one might consider testing the addition of BX to suitable soils in the field, perhaps using an agronomically relevant plant species, to test the potential of these maize exudates to be used for smarter and more sustainable agriculture.