PhD defence: The Salicylic Acid-Mediated Growth-Immunity Tradeoff in Arabidopsis

A major challenge for future agriculture is to have access to disease resistant crops to reduce or even completely ban the use of pesticides. An important solution to this challenge is to improve the innate immune system of plants, which requires detailed understanding of plant immunity.

In plants, immune responses are induced and regulated by plant hormones like salicylic acid. Plants depleted in salicylic acid are highly susceptible to pathogen infection whereas plants with high salicylic acid content are highly resistant to many diseases. Salicylic acid activates a plethora of immune responses, such as the production of antimicrobial molecules and the strengthening of the plant cell wall. However, these responses require energy and resources that are not invested in plant growth and development. In agricultural this would mean loss of crop yield. This trade-off also works the other way around, where strong growth and development can actively suppress immunity. The genetic components that regulate this growth-immunity trade-off are largely unknown.

In my thesis I focus on this trade-off and its regulators in the model plant Arabidopsis thaliana (thale cress). The research was performed with Arabidopsis mutants that accumulate high levels of salicylic acid and have a constitutively active immune system, but display dwarfed growth. In a genetic screen, suppressor mutants were found that restored growth while high disease resistance was maintained. The genes responsible for that were identified and revealed genetic mechanisms regulating the growth-immunity trade-off that can contribute to improving disease resistance of crops.