Plants are challenged by a diverse range of microbial pathogens and insect pests and have evolved countermeasures to resist most potential invaders. The outcome of the interaction of plants with a given pathogen is governed by several factors, including the genotype, the physiological state of the plant, environmental signals and, any specific interactions that might occur between the activated signaling pathways. Plants resist pathogen infection by inducing a defense response that is targeted specifically to combat invasion by the pathogen. In many cases, the induction of these responses is accompanied by localized cell death at the site of pathogen entry, which often is able to restrict the spread of pathogen to cell within and immediately surrounding the lesions. This phenomenon, known as the hypersensitive response, is one of the earliest visible manifestation of induced defense response and resembles programmed cell death in animals. Concurrent with hypersensitive response development, defense reactions are triggered locally and in parts distant from the site of primary infection. This phenomenon, known as systemic acquired resistance, is one of the most studied induced defense responses and is accompanied by a local and systemic increase in endogenous salicylic acid (SA) and a concomitant upregulation of a large set of defense genes.
Among various signaling molecules proposed to modulate defense responses, SA and jasmonic acid (JA) are widely believed to be the global regulators of plant defense signaling. These phytohormones elicit distinct responses and undergo extensive cross talk, which is likely to influence the amplitude and magnitude of various signals leading to a resistance response. JA and Methyl JA, collectively termed jasmonates, are potent biological regulators in plants that are formed in a multi step process initiated by oxygenation of the fatty acid (FA)-linolenic acid. Upon pathogen attack, FAs are liberated from their esterified forms and converted into oxylipins, a group of oxygenated FA derivatives. The enzymatic and non-enzymatic oxygenation of FAs results in the generation of a wide variety of compounds, many of which are found in plants and animals. In addition to their role as precursors of oxylipins, free FAs can also act as signaling messengers, regulate membrane fluidity and serve as an energy reserve.
The overall goal of our research is to help understand how specific signaling pathways are induced during host-pathogen interaction, how these pathways communicate with each other and the molecular mechanisms underlying such regulations. We are using Arabidopsis (www.arabidosis.org) as a model plant system and are studying its interaction with a viral pathogen turnip crinkle virus (TCV) and an oomycete pathogen Peronospora parasitica. With regards to signaling mechanisms our main interest is to decipher the role of fatty acid signaling pathways in plant defense.