Résumé
Banana streak viruses (BSV), which infect bananas and plantains (Musa spp.) worldwide, became a couple of decade ago, the major constraint for banana breeding programmes and Musa germplasm exchange. Indeed, the movement of germplasm and propagation of virus-free planting material have been restricted due to the discovery, in the genome of Musa balbisiana (noted B genome), of infective BSV integrations (eBSV) which can spontaneously release functional BSV virions following stresses. Our objective is to both study the mechanisms underlying the regulation of eBSV and gain knowledge on the BSV biology. Unfortunately to date, BSV is known to infect banana only which is a difficult/complex plant to work with because the life cycle is long, mutant databases are not available, transient and stable transformations are difficult and laborious for instance. To overcome most of those difficulties, we tried to infect the model plant Arabidopsis thaliana (A.t.). We firstly stably transformed two different At ecotypes with a viral clone containing more than one length copy (1,5) of BSOLV DNA genome via agrobacterium. This clone, previously selected as infectious in banana plants, contains twice the promoter region because of the poly A signal is located in front of the promoter. Out of the thirty T2 transformants we analysed, none of them showed abnormal phenotype or BSV symptoms. Besides, RT-PCR experiments showed that viral transcription was undetectable suggesting that T-DNA expression was inhibited at the transcriptional level. Using methylation sensitive restriction enzymes we indeed evidenced that the T-DNA was methylated. To overcome this problem, we transformed several A.t. mutants affected at different stage of the epigenetic RNA silencing pathway. Screening and characterization of primary transformants is on the way but preliminary results on dcl234 triple mutant background indicate that BSV transcription is detectable. Immuno-capture PCR experiments and electron microscopy observations will be soon carried out to look for the presence of the virus. (Texte intégral)