Project description:As a broad group, hemibiotrophic pathogens cause significant losses within agriculture threatening the sustainability of food systems globally. The complex manner in which these microbes colonize their hosts, including an initial biotrophic phase of colonization followed by a biotrophic-to-necrotrophic switch (BNS) phase and ending with a necrotrophic mode of nutritional acquisition, renders their management more complex than pathogens which display a single nutritional strategy. Within model plant systems, typically each of these phases is characterized by both common and discrete transcriptional responses as the host modulates physiological processes in concert with changes in pathogen biology. Plant hormones also play an important role in these stages with classic models showing that salicylic acid accumulates during the biotrophic phase and jasmonic acid/ethylene responses occur during the necrotrophic phase. In this study, we use the interaction between the hemibiotroph Phytophthora medicaginis and the roots of its host Cicer arietinum (chickpea) to define the duration of the different life stages of P. medicaginis during the pathogenesis of chickpea. Using transcriptional profiling across all three stages of infection we demonstrate that chickpea displayed some similarities in response to P. medicaginis as has been previously documented in other model plant-pathogen hemibiotrophic interactions. However, our transcriptomic results suggest that chickpea does not conform to the phytohormone response model observed in leaf colonization, nor to that observed for roots of other plant species being colonised by soil-borne hemibiotrophs. We confirm these findings using targeted quantification of salicylic acid and jasmonic acid. The findings from this study demonstrate that a wider spectrum of plant species should be investigated in future to understand the physiological changes in plants during the different stages of colonization by hemibiotrophic soil-borne pathogens before we can better manage these economically important microbes in agronomically relevant conditions.

Project description:Oomycetes from the genus Phytophthora are fungus-like plant pathogens that are devastating for agriculture and natural ecosystems. Due to particular physiological characteristics, no treatments against diseases caused by oomycetes are presently available. To develop such treatments, it appears essential to dissect the molecular mechanisms that determine the interaction between Phytophthora species and host plants. The present project is focused on the molecular mechanisms that underlie the compatible plant-oomycete interaction and plant disease.The laboratory developed a novel interaction system involving the model plant, Arabidopsis thaliana and Phytophthora parasitica, a soil-borne pathogen infecting a wide host range, thus representing the majority of Phytophthora species. A characteristic feature of the compatible Arabidopsis/Phytophthora parasitica interaction is an extended biotrophic phase, before infection becomes necrotrophic. Because the initial biotrophic phase is extremely short on natural (e.g. solanaceous) hosts, the Arabidopsis system provides the opportunity to analyze, for both interaction partners, the molecular events that determine the initiation of infection and the switch to necrotrophy.The present project aims at analyzing the compatible interaction between A. thaliana roots and Phytophthora parasitica. The Affymetrix A. thaliana full genome chip will be used to characterize modulations of the transcriptome occurring over a period of 24h from the onset of plant root infection to the beginning of necrotrophy. Parallel to this study, a custom designed Phytophthora parasitica biochip will enable analyzing of Phytophthora parasitica gene expression during the same stages. The pathosystem involving A. thaliana and Phytophthora parasitica was described in Attard A, Gourgues M, Callemeyn-Torre N, Keller H. 2010. The New phytologist 187: 449–460. The protocol for recovery of RNA from purified appressoria was described in Kebdani N, Pieuchot L, Deleury E, Panabieres F, Le Berre JY, Gourgues M. 2010. New Phytol 185: 248–257.

Project description:Oomycetes from the genus Phytophthora are fungus-like plant pathogens that are devastating for agriculture and natural ecosystems. Due to particular physiological characteristics, no treatments against diseases caused by oomycetes are presently available. To develop such treatments, it appears essential to dissect the molecular mechanisms that determine the interaction between Phytophthora species and host plants. The present project is focused on the molecular mechanisms that underlie the compatible plant-oomycete interaction and plant disease.The laboratory developed a novel interaction system involving the model plant, Arabidopsis thaliana and Phytophthora parasitica, a soil-borne pathogen infecting a wide host range, thus representing the majority of Phytophthora species. A characteristic feature of the compatible Arabidopsis/Phytophthora parasitica interaction is an extended biotrophic phase, before infection becomes necrotrophic. Because the initial biotrophic phase is extremely short on natural (e.g. solanaceous) hosts, the Arabidopsis system provides the opportunity to analyze, for both interaction partners, the molecular events that determine the initiation of infection and the switch to necrotrophy.The present project aims at analyzing the compatible interaction between A. thaliana roots and Phytophthora parasitica. The Affymetrix A. thaliana full genome chip will be used to characterize modulations of the transcriptome occurring over a period of 24h from the onset of plant root infection to the beginning of necrotrophy. Parallel to this study, a custom designed Phytophthora parasitica biochip will enable analyzing of Phytophthora parasitica gene expression during the same stages. The pathosystem involving A. thaliana and Phytophthora parasitica was described in Attard A, Gourgues M, Callemeyn-Torre N, Keller H. 2010. The New phytologist 187: 449–460. The protocol for recovery of RNA from purified appressoria was described in Kebdani N, Pieuchot L, Deleury E, Panabieres F, Le Berre JY, Gourgues M. 2010. New Phytol 185: 248–257. A series of 14 hybridizations corresponding to two biological replicates each corresponding to RNA extractions of the following biological conditions were used: 1-Vegetative mycelium (recovered from two samples of 4 day-old cultures in liquid V8 medium at 24°C), 2- Motile zoospores (recovered from 8 independent cultures), 3-Appressoria differentiated on onion epidermis (epidermis from 20 onion bulbs inoculated with zoospores collected from 8 independent Petri dishes); appressoria collected 3 hours after inoculation (24 °C), 5- Infection of A. thaliana roots by Phytophthora parasitica zoospores (samples recovered at 2.5, 6, 10.5 and 30 hours post inoculation; 5 inoculated plants for each sample).

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Functional genomics identifies a small secreted protein that plays a role during the biotrophic to necrotrophic shift in the root rot pathogen Phytophthora medicaginis

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