5.2 Hormone signaling
Significant work has been done to investigate plant hormone signaling crosstalk between biotic and abiotic stresses (for review see Shigenaga et al., 2017; Ku et al., 2018). This work has found ABA is a key regulator of abiotic stress and biotic stress responses. ABA is considered “the” abiotic stress hormone (Shigenaga et al., 2017), and through its antagonistic relationships with SA and JA/ET signaling pathways, it allows for crosstalk at multiple levels in biotic stress responses for both necrotrophic and biotrophic pathogens (Atkinson & Urwin, 2012; Kissoudis et al., 2014). Future research efforts should focus on ABA signaling pathways, along with their interaction with SA, JA/ET, to increase plant resilience to climate change. Other growth hormones have been implicated in biotic and abiotic stress responses, including gibberellin, cytokinin, auxin, and brassinosteroids (Kissoudis et al., 2014). Additionally, it has been recently demonstrated through genetic analysis that modification of epistatic interactions between the hormone jasmonate and the photoreceptor phyB uncoupled the plant growth and defense trade-off in Arabidopsis (Campos et al., 2016). This indicates that future breeding efforts involving hormone signaling may overcome growth-defense tradeoffs associated with combined biotic-abiotic stress responses.