The oomycete pathogen Phytophthora infestans causes late blight, an important disease in potato world wide. P. infestans secretes numerous effector molecules, some of which are recognized by host plants carrying resistance (R) genes. These effectors then act as avirulence (Avr) factors and elicit a hypersensitive response (HR) that arrests growth of the pathogen. Through a combined approach of genetic mapping and transcriptional profiling (cDNA-AFLP) we isolated an Avr gene that shows a gene-for-gene interaction with R4. This gene, named PiAvr4, is highly expressed in germinated cysts and encodes a 287 amino acid protein with a putative signal peptide and an RxLR-DEER motif. The Avr4 protein belongs to a large family of P. infestans effector proteins that are highly divergent but share the RxLR-DEER motif. This motif is thought to play a role in delivery of effectors into the host cell. Transformation of PiAvr4 into P. infestans isolates virulent on R4 plants, resulted in complementation, i.e., the transformants elicited HR and thus became avirulent on plants carrying R4. In planta expression of PiAvr4 using agroinfection-based Potato Virus X (PVX) expression vectors caused an HR specifically on R4 plants but not on r0 plants. However, the HR was only observed when a signal peptide sequence was included in the construct and not when the mature protein was produced. Apparently, ER modification and/or secretion of Avr4 are required for recognition of Avr4 as avirulence factor. Direct virus inoculation of plants with PVX expressing PiAvr4 with and without signal peptide sequence gave the same results as the agroinfection inoculation.
|Title of host publication||Book of Abstracts Oomycete Molecular Genetics Network Workshop, Pacific Grove, California, USA 18-20 March 2007|
|Publication status||Published - 2007|