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Osman Telli

PhD Student

Osman is studying for a PhD in plant-microbe interactions, particularly in the area of circadian regulation of pathogenicity.

Director of Studies: Dr Mahmut Tör, National Pollen and Aerobiology Research Unit, Institute of Science and the Environment, University of Worcester, UK.

Project: “Investigating Circadian regulations of effectors in the oomycete pathogen Hyaloperonospora arabidopsidis”.

Downy mildew is the common name of a highly specialized important group of obligate biotrophic plant parasites. They belong to oomycete group of eukaryotic microorganisms and contain economically important crop pathogens.

Circadian clocks are endogenous cellular timekeepers that control a wide variety of daily physiological and molecular rhythms in most eukaryotic and at least some prokaryotic organisms. These rhythmic events allow organisms to adapt to the natural environment on earth. Recently, a key functional link between the circadian clock and the plant immunity using the Arabidopsis-downy mildew system has been revealed (Wang et al. 2011).

It has been known that all circadian rhythms share three basic properties. First, circadian rhythms persist under constant conditions with a period length of about 24h. Second, they can be entrained (reset) by environmental cues, with light and temperature being the most important signals. Third, the rhythms are temperature compensated. Despite disparate phylogenetic origins and vast differences in complexity among the species that show circadian rhythmicity, at the core of all known circadian clocks is at least one internal autonomous circadian oscillator. These oscillators contain positive and negative elements that form autoregulatory feedback loops, and in many cases these loops are used to generate 24-hour timing circuits. Components of these loops can directly or indirectly receive environmental input to allow entertainment of the clock to environmental time and transfer temporal information through output pathways to regulate expression of rhythmic clock-controlled genes (CCG) and rhythmic biological activity (Pando et al. 2002).

In this study, we we will use the model plant Arabidopsis thaliana and its native pathogen Hyaloperonospora arabidopsidis (Hpa), the causative agent of the downy mildew disease. Our main aims are to investigate if Hpa is affected by the circadian rhythm and if so how the pathogen regulates this rhythm; whether the rhythm is important for its pathogenicity, and more importantly whether selected effectors show circadian regulated rythmic expression patterns.