Hop stunt viroid (HSVd) sequence variants from Prunus species: evidence for recombination between HSVd isolates.

Abstract

Hop stunt viroid (HSVd) is able to infect a number of herbaceous and woody hosts, such as grapevine, Citrus or Prunus plants. Previous phylogenetic analyses have suggested the existence of three major groups of HSVd isolates (plum-type, hop-type and citrus-type). The fact that these groups often contain isolates from only a limited number of isolation hosts prompted the suggestion that group-discriminating sequence variations could, in fact, represent host-specific sequence determinants which may facilitate or be required for replication in a given host. In an effort to further understand the relationships between HSVd and its different hosts, HSVd variants from eight naturally infected Prunus sources, including apricot, peach and Japanese plum have been cloned and sequenced. In total, ten

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

“…The insertion into the "cachexia expression motif" of two nucleotides (+A115, +U189) potentially forming a base-pair did not abolish the infectivity, but the resulting variant did not induce symptoms. These two nucleotides, which are present in most non-cachexia inducing variants of HSVd have been found in other variants recovered from citrus (Velázquez et al, 2002), almond (Cañizares et al, 1997), Prunus (Kofalvi et al, 1997) and grapevine (Puchta et al, 1989), thus confirming that their presence or absence does not impair infectivity. Similarly, the U197→C transition responsible for the shift from severe to mild symptoms is also present in different sources of HSVd (Ragozzino et al, 2004;Ito et al, 2006).…”

“…Estudios en plantas infectadas con PSTVd, CEVd (Tabler y Sänger, 1984, Visvader y Symons, 1983) y posteriormente con la mayoría de especies conocidas han mostrado que las infecciones viroidales siguen una dinámica parecida y se encuentran en el huésped mezclas de secuencias más o menos complejas (Rakowsky y Symons, 1989, Hernández y Flores, 1992, Ridgen y Rezaian, 1993, Ambrós et al 1995, Polivka et al 1996, Kofalvi et al 1997, Navarro 1997, PalacioBielsa et al 2004, Gandia y Duran-Vila, 2004. El número y la frecuencia de las distintas secuencias definen la variabilidad de una población.…”

“…These results confirmed with an artificial variant the requirement of the "cachexia expression motif" for symptom development as described by Reawankaron and Semancik (1998). Even though effects due to changes in the V domain have not been reported in other members of the family Pospiviroidae, the "cachexia motif" and "non-cachexia motif" of the V domain of HSVd play a relevant role, not only for its implication in pathogenicity but also by carrying the host-specific changes identified in isolates recovered from different crops (Cañizares et al, 1997;Kofalvi et al, 1997;Amari et al, 2001). …”

Questions and Concepts in Plant Virus Evolution: a Historical Perspective

“…Selection was associated with the need to maintain a functional structure, for instance, in the capsid protein of tobamoviruses (Altschuh et al 1987) or in noncoding subviral pathogenic nucleic acids such as satellites or viroids (Fraile and Garcia-Arenal 1991;Elena et al 1991). Host-associated selection, already known from passage experiments, was also invoked to explain population structure, for instance, in Kennedya yellow mosaic virus (KYMV; Skotnicki et al 1996), Hop stunt viroid (Kofalvi et al, 1997) or Barley yellow dwarf virus (BYDV; Mastari et al, 1998). Evidence of vector-associated selection initially derived from loss of transmissibility upon mechanical passage or vegetative propagation of the virus host (Reddy and Black 1977).…”

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

“…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.…”