Plants have evolved the ability to detect invading microbes by perceiving elicitor, called Pathogen- and Damage-Associated Molecular Patterns (PAMPs and DAMPs), that trigger PAMP-Triggered Immunity (PTI). Activation of defense responses during PTI is costly and, in the absence of pathogen pressure, might reduce fitness. For instance, accumulation of high levels of oligogalacturonides (OGs), a plant DAMP, in Arabidopsis OG-M transgenic plants, leads to severe growth reduction. On the other hand, plants treated with elicitors show increased resistance to fungal infection without constitutive expression of defenses. This resistance is likely due to a ¿primed¿ status, where elicited plants are able to respond more quickly and efficiently to subsequent infections. We have recently identified two Arabidopsis genes that are required for elicitor-induced resistance against fungal infection: LYK2, encoding a LysM-Receptor-like Kinase, and PCaP1, encoding a plasma membrane protein involved in the transport of cations. The molecular mechanism underlying the priming phenomenon is not fully elucidated, though it might involve epigenetic changes. Moreover, the basis of the reduced growth observed in OG-treated plants is not clear. We propose to dissect the signaling pathways involved in OG-induced growth reduction, to identify defense-related genes that undergo priming of their expression upon elicitor pre-treatment and to investigate potential epigenetic changes in these genes, to elucidate the molecular basis of elicitor-induced resistance and of the trade-off between defense and growth in plants.
Despite priming of defense responses by biotic and abiotic agents has been known for years, the molecular mechanisms that lead to a primed state in plants treated with biological elicitors and make them more resistant to pathogenic microorganisms are largely unknown. Moreover, it is still unclear how plants integrate the perception of multiple MAMPs and DAMPs into a robust and effective response, and how different signaling pathways are integrated to ensure a proper balance between immune responses and growth. This project will elucidate multiple elements of defense priming and of the tradeoff between growth and defense in plants, taking advantage of the innovative tools available in the laboratory (plants expressing the OG-Machine fusion protein; mutants impaired in elicitor-induced resistance to pathogens).
Pathogen attack has a significant impact on crop field production, and research on understanding the way the plant immune system works is crucial to creating new tools to solve agricultural issues. Induced resistance using priming agents potentially offers an efficient, cost-effective and environmentally sound way to protect crops with significant benefits under conditions of disease occurrence. Priming has substantial effects on plant growth and seed production that depend on the extent of disease pressure, and likely leads to transgenerational effects that might protect the progeny of primed plants, but might also impair crop production reducing vegetative growth and reproduction. Given the fact that growth and seed set are crucial for the ecological performance of plants, it is plausible that priming plays an essential role in nature. Knowledge acquired in this project may therefore be exploited to improve crops resistance to biotic stresses, associated with an optimization of growth and yield.