Ilyas, Muhammad (2014). The role of papain-like cysteine proteases of tomato in pathogen defense. PhD thesis, Universität zu Köln.

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Abstract

Recognition and induction of plant immune responses by microbial pathogens is a dynamic process that requires signalling mechanisms associated with defense. Tomato is a host for the fungus Cladosporium fulvum and the oomycete Phytophthora infestans. The Cf2 resistance gene of tomato confers recognition of the Avr2 avirulence gene of Cladosporium fulvum. The Avr2 gene encodes a small secreted protein that inhibits the cysteine proteases Rcr3 and PIP1 in the apoplast of tomato leaves. The perception mechanism involving PIP1 is not yet fully understood. Rcr3, on the other hand, is required for Cf2-mediated perception of Avr2. This indirect perception mechanism is consistent with the guard model, which predicts that Rcr3 is a virulence target of Avr2, guarded by the Cf2 resistance gene product. The higher abundance of PIP1 compared to Rcr3, however, suggests that Rcr3 is rather a decoy that only functions in Avr2 perception. Here we show that silencing of PIP1 in the transgenic tomato enhances C. fulvum susceptibility, whereas rcr3 mutant plants do not show increased susceptibility in the absence of Cf2, consistent with the decoy model. Rcr3 and PIP1 are also inhibited by Epic1 and Epic2B, which are secreted cystatin-like proteins produced by P. infestans during infection. Epics are not recognized through the Rcr3-Cf2 perception system, but Cf2/rcr-3-3 mutant plants are more susceptible for P. infestans when compared to Cf2/Rcr3 plants, suggesting a role for Rcr3 in P. infestans resistance in the absence of Epic recognition. Here we found that Cf0/rcr3-3 mutant plants are also more susceptible to P. infestans when compared to Cf0/Rcr3 plants. The Cf0/Rcr3 plants are even more resistance when compared to Cf2/Rcr3 plants indicating that other genetic factors in addition to Rcr3 contribute to P. infestans immunity. In the last part of this thesis we studied the role of natural variation in Rcr3 and PIP1 in the interaction with Avr2, Epic1 and Epic2B. We show that part of the diversity observed in Rcr3 plays a role in differential interactions with the effectors and may be important in pathogen recognition. In contrast, only slight phenotypic differences could be observed between allelic variants of PIP1, which may be due to conservation of PIP1 function. In conclusion, the role of Rcr3 and PP1 in immunity and observed natural variation in Rcr3 and PIP1 affecting interactions with inhibitors illustrate an interesting protease-inhibitor arms race at the plant-pathogen interface.

Item Type: Thesis (PhD thesis)
Creators:
CreatorsEmailORCID
Ilyas, Muhammadilyas@mpipz.mpg.deUNSPECIFIED
URN: urn:nbn:de:hbz:38-56244
Subjects: Life sciences
Agriculture
Uncontrolled Keywords:
KeywordsLanguage
Plant microbe interaction, plant proteases, C. fulvum, p. infestansUNSPECIFIED
Faculty: Faculty of Mathematics and Natural Sciences
Divisions: Faculty of Mathematics and Natural Sciences > MPI for Plant Breeding Research
Language: English
Date: 17 June 2014
Date of oral exam: 22 June 2012
Referee:
NameAcademic Title
SchulzeLefert, PaulProf.Dr.
Refereed: Yes
URI: http://kups.ub.uni-koeln.de/id/eprint/5624

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