Timing is everything: Plant response to sequential and combinatorial stressors of herbivores and flooding

As climate change increases the frequency of biotic and abiotic stressors to crops, such as insect herbivory and flooding, the ability of plants to respond and mount appropriate defense strategies becomes more important for safeguarding our food supply. While many studies have examined single stressors, and few have looked at combined stressors, there is a knowledge gap in studies including consequence of sequential insect herbivory and flooding. We investigated gene expression and plant hormone differences in response between tomato plants challenged with a contrasting sequence of stressors (flooding fi­­rst for 24h, the­n herbivory added for 24h compared to herbivory first for 24h, then flooding added for 24h), as well as control plants with no stress exposure.
Results demonstrated significant differences between single and combined stresses for levels of plant hormones Jasmonic Acid (JA), Salicylic Acid (SA) and Abscisic Acid (ABA). Transcriptomic analysis revealed plants in both treatments under single stress showed increased expression for defense response and hormone-mediated signaling pathways (including JA). Meanwhile, plants exposed to different single stressors showed contrasting expression patterns. Additionally, both groups exposed to combined stress had increased expression for JA-signaling pathways, and decreased expression in photosynthetic processes, DNA replication, and RNA processing. Plants exposed to 48h flooding + 24h herbivory showed increased expression in SA- and ABA-signaling pathways. Results reveal differences in plant response arising from the order of stress exposure and underscores the need for further studies investigating plant-insect interactions in combination with climate change-related abiotic stressors.