Plant immune system incompatibility and the distribution of enemies in natural hybrid zones

Natural plant hybrid zones have been described as ‘sinks’ and ‘centers of biodiversity’ for herbivores and fungal pathogens. Jasmonic acid is known to be a critical signaling molecule for defense against these enemies. Does inhibition of jasmonic acid perhaps contribute to the susceptibility of hybrid plants to attack by herbivores? Here, we discuss recent evidence that plant immune system incompatibilities are likely to downregulate jasmonic acid (JA)-dependent responses through their effect on expression of the salicylic acid (SA)-dependent pathway. Because these hybrid immune incompatibilities are a function of environmental temperatures, they suggest a dependency between attack rates in hybrid zones and environmental conditions. Hybrid zones in colder environments, for example at higher elevations or latitudes, are more likely to exhibit elevated SA, suppressed jasmonic acid-dependent defenses, and lower resistance to herbivores and other necrotrophic pathogens.