Field and acclimated metabolomes of a resurrection plant suggest strong environmental regulation in the extreme end of the species’ range

Plant secondary metabolites are significant mediators of the interactions of plants with their environment. The desiccation tolerant “resurrection plant” Myrothamnus flabellifolia Welw. is distributed throughout southern Africa and is vicariantly separated between arid Namibia and the comparatively mesic South Africa where it is subjected to contrasting climate regimes. Our earlier study indicated that these populations were metabolomically and phylogenetically distinct, leading us to hypothesise that the metabolic signature of the arid-adapted plants from Namibia was environmentally determined. To test this, we profiled the metabolomes of plants from both regions that had been sampled directly in the field (non-acclimated) with those of plants from the same regions that had been long-term acclimated in a greenhouse (acclimated). Long-term acclimation resulted in a convergence of the metabolic profiles of the plants collected from the different regions. However, while the South African plants demonstrated little difference between their acclimated and non-acclimated metabolomes, the metabolomes of the acclimated Namibian samples were distinct from those of the plants sampled in the field in Namibia. Further scrutiny of the metabolite differences between the acclimated and non-acclimated Namibian samples revealed several metabolites that were significantly more abundant in the field samples, and we propose that these might contribute to survival in this region. To further test the metabolomic response from a temporal perspective, we subjected the acclimated plants to short-term high-temperature treatment in climate chambers. However, this treatment had no significant impact on the metabolomes of the plants. Our findings suggest that long-term, rather than short-term, environmental conditions warrant large-scale reprogramming of the metabolome in M. flabellifolia, and that the climate conditions in the more arid region of the species’ range necessitate the production of particular phenolic metabolites.