Plants live in close association with microbes, which can influence the expression of plant traits, and recent evidence suggests that below ground microbial communities can shift plant traits in ways that mitigate the negative effects of stress on plant fitness. Here, we investigate whether these microbe-effects extend to the offspring generation and influence transgenerational plasticity (maternal effects) in their plant hosts. We used Brassica rapa seeds from an experiment in which plants were grown in either drought or well-watered conditions in association with microbial communities that had been evolving for 16 months in either drought or well-watered conditions to determine how the maternal environment (dry or wet soil conditions and drought vs. wet adapted microbial communities) affected seedling traits and drought tolerance in the offspring.
Results/Conclusions
On average, offspring from mothers grown in association with dry-adapted microbial communities germinated 4 days earlier than offspring from mothers grown in association with wet-adapted microbial communities (F1,247 = 7.42, P < 0.007); these effects were especially apparent when maternal plants were grown in dry environments and originated from plant populations that had evolved under dry conditions for three generations (Microbe history x Drought x Plant evolutionary history interaction: F1,247 = 4.67, P < 0.032). These early effects on germination also led to differences in seedling size as offspring from mothers grown in association with dry adapted microbes were significantly larger than offspring from mothers grown in association with wet adapted microbes (F1,238 = 5.93, P < 0.016). Our findings indicate that microbial communities influence transgenerational plasticity in plant hosts. As a result, the transgenerational plasticity observed in response to many types of stressors may not only be due to the stress but could also be the result of microbial responses to stress. Ongoing work will allow for tests of whether these plastic responses are adaptive.