Doctoral Researchers

Ullah, Chhana

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JSMC Fellow

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Max Planck Institute for Chemical Ecology
Dept. of Biochemistry
PhD Project:

Chemical communication between biotrophic and necrotrophic pathogens and a woody plant host: Signaling, defense reactions, and the cost of defense


Abstract: Plants are subject to infection by two different classes of pathogens: biotrophic pathogens, which infect plant cells but do not actually kill them, and necrotrophic pathogens, which...
... obtain their nutrients from dead or dying cells. Biotrophs are known to communicate closely with plants via effector proteins that maintain pathogenesis. Plant R-protein receptors are designed to recognize the effector proteins of biotrophs and signal a defense response, but biotrophs may be able to evade recognition. In contrast, the communication of necrotrophs with their hosts is much less well understood. Plants are hypothesized to recognize necrotrophs by the pattern of molecules produced on infection and respond by synthesizing defensive compounds. But, it is unclear how plant defenses function against necrotrophic vs. biotrophic pathogens given the different scales of contact and types of communication. Necrotrophic infection must be opposed by blocking pathogen growth at a distance from living plant cells, while biotrophs need to be selectively killed within living cells. Not enough is known about which plant compounds are active in defense to determine how they target different pathogen types. Moreover, rarely has anyone considered the costs of antifungal defenses to the plant for different pathogen types. Many pathogens are not necessarily fatal to woody plants. It would be valuable to compare the potential loss of tissue to pathogens and the costs of defending it by measuring carbon and nutrient allocation patterns in plants manipulated to be both with and without defenses. These results should give unique insights into the optimization of plant defense strategies. In recent years, many species of poplar (Populus) have gained economic importance due to their fast growth and use for bio-fuel and timber. The availability of a complete genome for one species has quickly established Populus as the best model system in woody plant research. However, under natural conditions, poplar trees face a plethora of biotrophic and necrotrophic pathogens. In their leaves and bark, poplars synthesize high quantities of polyphenolic metabolites, including proanthocyanidins, flavonoids and salicinoids, which may have anti-fungal properties. Although similar compounds are present in many other woody plant species, their benefit in defense against pathogens of different types and their metabolic costs are still poorly understood. We propose to compare plant-pathogen interactions between black poplar (P. nigra), a species native to Germany, and its two most important pathogens, the biotrophic poplar rust (Melampsora larici-populina) and the necrotrophic poplar canker (Cryptodiaporthe populea). The project will exploit the genomic sequence obtained from Populus trichocarpa, our knowledge of poplar polyphenolic metabolites thought to be important in anti-fungal defense, and the ecological, chemical and molecular platforms already established for studying poplar-herbivore interactions in our laboratory. The goal is to understand: (1) the differences in communication between poplar and biotrophic vs. necrotrophic pathogens (2) how these affect the strategies of plant defense, and (3) the costs and benefits of such defense.