RESUMEN
Potato spindle tuber viroid (PSTVd) belongs to plant-pathogenic, circular, non-coding RNAs. Its propagation is accompanied by (mis)regulation of host genes and induction of pathogenesis symptoms including changes of leaf morphogenesis depending on the strength of viroid variant. We found strong genotype-dependent suppression of tomato morphogenesis-regulating transcription factor SANT/HTH-Myb (SlMyb) due to viroid pathogenesis. Its relative mRNA level was found to be significantly decreased in PSTVd-sensitive tomato (cvs Rutgers and Heinz 1706) due to degradation processes, but increased in PSTVd-tolerant (cv. Harzfeuer). In heterologous system of Nicotiana benthamiana, we observed a SlMyb-associated necrotic effect in agroinfiltrated leaf sectors during ectopic overexpression. Leaf sector necroses were accompanied by activation of nucleolytic enzymes but were suppressed by a strongly pathogenic PSTVd variant. Contrary to that, PSTVd's effect was inhibited by the silencing suppressor p19. It was found that in both, Solanum lycopersicum leaves and N. benthamiana leaf sectors, SlMyb mRNA degradation was significantly stronger in viroid-infected tissues. Necroses induction as well as gene silencing experiments using the SANT/HTH-Myb homologues revealed involvement of this Myb in physiological changes like distortions in flower morphogenesis and growth suppression.
Asunto(s)
Nicotiana/genética , Reguladores del Crecimiento de las Plantas/genética , Proteínas de Plantas/genética , Solanum lycopersicum/genética , Factores de Transcripción/genética , Viroides/genética , Interacciones Huésped-Patógeno , Solanum lycopersicum/metabolismo , Solanum lycopersicum/virología , Datos de Secuencia Molecular , Enfermedades de las Plantas/genética , Enfermedades de las Plantas/virología , Reguladores del Crecimiento de las Plantas/metabolismo , Hojas de la Planta/crecimiento & desarrollo , Hojas de la Planta/metabolismo , Hojas de la Planta/virología , Proteínas de Plantas/metabolismo , ARN Mensajero/genética , ARN Mensajero/metabolismo , ARN Pequeño no Traducido/genética , ARN Pequeño no Traducido/metabolismo , ARN Viral/genética , ARN Viral/metabolismo , Análisis de Secuencia de ARN , Nicotiana/metabolismo , Nicotiana/virología , Factores de Transcripción/metabolismo , Viroides/patogenicidad , Viroides/fisiologíaRESUMEN
Viroid-caused pathogenesis is a specific process dependent on viroid and host genotype(s), and may involve viroid-specific small RNAs (vsRNAs). We describe a new PSTVd variant C3, evolved through sequence adaptation to the host chamomile (Matricaria chamomilla) after biolistic inoculation with PSTVd-KF440-2, which causes extraordinary strong ('lethal') symptoms. The deletion of a single adenine A in the oligoA stretch of the pathogenicity (P) domain appears characteristic of PSTVd-C3. The pathogenicity and the vsRNA pool of PSTVd-C3 were compared to those of lethal variant PSTVd-AS1, from which PSTVd-C3 differs by five mutations located in the P domain. Both lethal viroid variants showed higher stability and lower variation in analyzed vsRNA pools than the mild PSTVd-QFA. PSTVd-C3 and -AS1 caused similar symptoms on chamomile, tomato, and Nicotiana benthamiana, and exhibited similar but species-specific distributions of selected vsRNAs as quantified using TaqMan probes. Both lethal PSTVd variants block biosynthesis of lignin in roots of cultured chamomile and tomato. Four 'expression markers' (TCP3, CIPK, VSF-1, and VPE) were selected from a tomato EST library to quantify their expression upon viroid infection; these markers were strongly downregulated in tomato leaf blades infected by PSTVd-C3- and -AS1 but not by PSTVd-QFA.
