Characterization of citrus HSVd isolates

Abstract

Seven citrus isolates of Hop stunt viroid (HSVd) were subjected to retrotranscription and DNA amplification (RT-PCR), cloning and sequencing. Single stranded polymorphism (SSCP) analysis demonstrated the existence of variability among and within cachexia inducing sources of HSVd. The electrophoretic profiles of SSCP appeared to be able to discriminate between non-cachexia and cachexia sources of HSVd. Sequence analysis demonstrated that the variable (V) domain was very conserved among the cachexia variants. Five nucleotide differences, affecting both the upper (3 nucleotides) and the lower (2 nucleotides) strands of the V domain, were identified as a motif discriminating cachexia and non-cachexia sequences. These five nucleotides affect the organization of a short helical region and two flanking loops of the V domain probably modifying the three-dimensional geometry of the molecule. The stability of the minimum free energy rod-like conformation of the cachexia sequences is lower than the non-cachexia. Information regarding the host effect on the evolution and variability of viroid quasispecies is also provided.

Citrus exocortis viroid and Hop Stunt viroid Doubly infecting grapevines in Brazil

“…Interestingly, these changes affected neither the secondary structure nor the TCH motif and the main nucleotides in the CCR domain (data not shown). On the other hand, in contrast to previous results for citrus HSVd isolates (Palacio-Bielsa et al, 2004), we observed some changes in the C domain for the grapevine HSVd clones analyzed here.…”

Effect of citrus hosts on the generation, maintenance and evolutionary fate of genetic variability of citrus exocortis viroid

“…However, Teycheney et al (2005) showed that, in general, RT-PCR produced less than 0.5 % errors. In addition, a previous work characterizing CEVd and HSVd diversity indicated that the observed mutations were unlikely to be due to PCR errors (Palacio & DuranVila, 1999;Palacio-Bielsa et al, 2004). In fact, some of the polymorphisms discussed here, such as the most frequent haplotypes (i.e.…”

“…This polymorphic population structure arises as a result of (i) the high mutation rates inherent to the cellular DNA-dependent RNA polymerases involved in viroid replication subverted to replicate an RNA template and (ii) the diverse and fluctuating selective pressures imposed by the different host species. Surveys of diversity have been performed for different viroid species, including pospiviroidae such as citrus exocortis viroid (CEVd) (Visvader & Symons, 1985;Gandía et al, 2005Gandía et al, , 2007, citrus dwarfing viroid (formerly citrus viroid III) (Owens et al, 2000), citrus bent leaf viroid (Foissac & Duran-Vila, 2000;Gandía & Duran-Vila, 2004), potato spindle tuber viroid (PSTVd) (Gó ra et al, 1994;Gruner et al, 1995;Gó ra-Sochacka et al, 1997), hop stunt viroid (HSVd) (Kofalvi et al, 1997;Palacio-Bielsa et al, 2004) and grapevine yellow speckle viroid 1 (Rigden & Rezaian, 1993;Polivka et al, 1996), as well as avsunviroidae such as chrysanthemum chlorotic mottle viroid (Navarro & Flores, 1997; Codoñer et al, 2006), peach latent mosaic viroid (Hernández & Flores, 1992;Ambró s et al, 1998Ambró s et al, , 1999 and avocado sunblotch viroid (Rakowski & Symons, 1989). CEVd is a member of the genus Pospiviroid within the family Pospiviroidae.…”

Estudios de Patogenicidad de Viroides del Género Apscaviroide y Hostuviroide en cítricos.

“…Se ha comprobado que infecciones naturales de CVd-IIa y CVd-IIb, dos tipos de variantes de HSVd en cítricos, tienen distintas dinámicas poblacionales, siendo las poblaciones de las variantes tipo CVd-IIa mucho más homogéneas que las del tipo CVd-IIb (Palacio-Bielsa et al 2004). …”

“…Normalmente la denominada secuencia maestra suele ser la de mayor tasa de infectividad. Inoculaciones con secuencias alternativas del aislado, o alteradas artificialmente, pueden no ser infectivas o acabar revirtiendo a la secuencia maestra para lograr infectar a la planta (Gandia y Duran-Vila, 2004). Aunque en una población viroidal cualquier mutación puntual es posible, aquellas que conllevan la perdida de funciones esenciales como la replicación o el movimiento del viroide, tienden a desaparecer dentro de la población.…”