A. Gora et al., USE OF INTRAMOLECULAR CHIMERAS TO MAP MOLECULAR DETERMINANTS OF SYMPTOM SEVERITY OF POTATO SPINDLE TUBER VIROID (PSTVD), Archives of virology, 141(11), 1996, pp. 2045-2055
Nucleotide sequence comparison shows that sequence variations are most
ly clustered in the P (pathogenicity) and V (variable) domains of the
potato spindle tuber viroid (PSTVd) molecule. Although these compariso
ns suggest the P domain as the primary determinant of PSTVd symptom se
verity, the potential contribution of the V domain has never been anal
ysed in detail. To investigate the relationship between the structure
of these domains and pathogenicity, six intraspecific chimeric PSTVd v
ariants were constructed by exchanging P and V domains between a mild
and two different severe PSTVd isolates. Infectivity studies showed th
at the P domain is directly responsible for the severity of symptoms i
nduced in tomato. The four recombinants containing a P domain from a s
evere isolate caused severe symptoms including severe epinasty, stunti
ng and veinal necrosis: while the two chimeras containing the mild iso
late P domain induced only mild symptoms. Quantitation of viroid accum
ulation in plants infected with the various recombinants suggests that
, with the constructions used, symptom severity did not correlate with
viroid accumulation, indicating that the P domain did not influence s
ymptom production through this simple mechanism.