Optimal Defense Theory 2.0: tissue-specific stress defense prioritization as an extra layer of complexity.

In nature, plants need to be able to quickly adapt to changing environments during their lifetime in order to maintain fitness. Different defense responses are not only costly, but often also antagonistic to one another. Hence, when faced with multiple stresses simultaneously, plants likely have to prioritize their defense responses.

Balancing trade-offs between biotic and abiotic stress responses through leaf age-dependent variation in stress hormone cross-talk.

In nature, plants must respond to multiple stresses simultaneously, which likely demands cross-talk between stress-response pathways to minimize fitness costs. Here we provide genetic evidence that biotic and abiotic stress responses are differentially prioritized in leaves of different ages to maintain growth and reproduction under combined biotic and abiotic stresses. Abiotic stresses, such as high salinity and drought, blunted immune responses in older rosette leaves through the phytohormone abscisic acid signaling, whereas this antagonistic effect was blocked in younger rosette leaves by , a signaling component of the defense phytohormone salicylic acid.

The Defense Phytohormone Signaling Network Enables Rapid, High-Amplitude Transcriptional Reprogramming during Effector-Triggered Immunity.

The phytohormone network consisting of jasmonate, ethylene, PHYTOALEXIN-DEFICIENT4, and salicylic acid signaling is required for the two modes of plant immunity, pattern-triggered immunity (PTI), and effector-triggered immunity (ETI). A previous study showed that during PTI, the transcriptional responses of over 5000 genes qualitatively depend on complex interactions between the network components. However, the role of the network in transcriptional reprogramming during ETI and whether it differs between PTI and ETI remain elusive.

Pathogen exploitation of an abscisic acid- and jasmonate-inducible MAPK phosphatase and its interception by immunity.

Phytopathogens promote virulence by, for example, exploiting signaling pathways mediated by phytohormones such as abscisic acid (ABA) and jasmonate (JA). Some plants can counteract pathogen virulence by invoking a potent form of immunity called effector-triggered immunity (ETI). Here, we report that ABA and JA mediate inactivation of the immune-associated MAP kinases (MAPKs), MPK3 and MPK6, in ABA induced expression of genes encoding the protein phosphatases 2C (PP2Cs), , , and through ABF/AREB transcription factors.

Evolution of Hormone Signaling Networks in Plant Defense.

Studies with model plants such as Arabidopsis thaliana have revealed that phytohormones are central regulators of plant defense. The intricate network of phytohormone signaling pathways enables plants to activate appropriate and effective defense responses against pathogens as well as to balance defense and growth. The timing of the evolution of most phytohormone signaling pathways seems to coincide with the colonization of land, a likely requirement for plant adaptations to the more variable terrestrial environments, which included the presence of pathogens.

Towards engineering of hormonal crosstalk in plant immunity.

Plant hormones regulate physiological responses in plants, including responses to pathogens and beneficial microbes. The last decades have provided a vast amount of evidence about the contribution of different plant hormones to plant immunity, and also of how they cooperate to orchestrate immunity activation, in a process known as hormone crosstalk. In this review we highlight the complexity of hormonal crosstalk in immunity and approaches currently being used to further understand this process, as well as perspectives to engineer hormone crosstalk for enhanced pathogen resistance and overall plant fitness.