title: Silencing of the PiAvr3a effector-encoding gene from Phytophthora infestans by transcriptional fusion to a short interspersed element.
abstract: Phytophthora infestans is the notorious oomycete causing late blight of potato and tomato. A large proportion of the P. infestans genome is composed of transposable elements, the activity of which may be controlled by RNA silencing. Accumulation of small RNAs is one of the hallmarks of RNA silencing. Here we demonstrate the presence of small RNAs corresponding to the sequence of a short interspersed retrotransposable element (SINE) suggesting that small RNAs might be involved in silencing of SINEs in P. infestans. This notion was exploited to develop novel tools for gene silencing in P. infestans by engineering transcriptional fusions of the PiAvr3a gene, encoding an RXLR avirulence effector, to the infSINEm retroelement. Transgenic P. infestans lines expressing either 5'-infSINEm::PiAvr3a-3' or 5'-PiAvr3a::SINEm-3' chimeric transcripts initially exhibited partial silencing of PiAvr3a. Over time, PiAvr3a either recovered wild type transcript levels in some lines, or became fully silenced in others. Introduction of an inverted repeat construct was also successful in yielding P. infestans transgenic lines silenced for PiAvr3a. In contrast, constructs expressing antisense or aberrant RNA transcripts failed to initiate silencing of PiAvr3a. Lines exhibiting the most effective silencing of PiAvr3a were either weakly or non-pathogenic on susceptible potato cv. Bintje. This study expands the repertoire of reverse genetics tools available for P. infestans research, and provides insights into a possible mode of variation in effector expression through spread of silencing from adjacent retroelements.
authors: Department of Plant Biology and Forest Genetics, Uppsala BioCenter, SLU, 750 07 Uppsala, Sweden.
authors: Ramesh R
authors: RR
authors: Vetukuri
authors: Zhendong
authors: Z
authors: Tian
authors: Anna O
authors: AO
authors: Avrova
authors: Eugene I
authors: EI
authors: Savenkov
authors: Christina
authors: C
authors: Dixelius
authors: Stephen C
authors: SC
authors: Whisson
mesh_terms: D020868:Gene Silencing; D055750:Phytophthora infestans / Q000235:genetics* / Q000378:metabolism / Q000472:pathogenicity; D010935:Plant Diseases / Q000469:parasitology; D059386:Reverse Genetics / Q000379:methods*; D020086:Short Interspersed Nucleotide Elements; D011198:Solanum tuberosum / Q000469:parasitology; D014158:Transcription, Genetic; D014774:Virulence; D037521:Virulence Factors / Q000235:genetics* / Q000378:metabolism
chemical_list: C562170:AVR3a protein, Phytophthora infestans; D037521:Virulence Factors