عنوان

Molecular basis for the cachexia disease syndrome of citrus

TLpq304353782

انگلیسی

Molecular basis for the cachexia disease syndrome of citrus

[Thesis]

K. Reanwarakorn

J. S. Semancik

University of California, Riverside

1997

161

Ph.D.

University of California, Riverside

1997

Citrus viroid group II with 295-302 nts, consists of cachexia-inducing variants, CVd-IIb (Citrus cachexia viroid, CCaVd), CVd-IIc, Ca-903, Ca-909 and a single non-cachexia inducing variant, CVd-IIa. Parson's special mandarin (PSM) expressed gumming and stem pitting when inoculated only with cachexia-inducing variants. CVd-IIa infection resulted in strong symptoms of short internodes and rugous leave on luffa (Luffa aegyptiaca) while cachexia variants induced mild symptoms. Cachexia-inducing variants, CVd-IIb and CVd-IIc produced classical cachexia type symptoms of gumming and stem pitting on PSM, Orlando tangelo (OT) and Citrus macrophylla. However, Palestine sweet lime (PSL), the indicator of xyloporosis, displayed a simple fine pitting reaction with infection by both CVd-IIb and CVd-IIc. The nucleotide sequence of CVd-IIc although differing from CVd-IIb was identical with a variant common to xyloporosis sources from Israel. Thus, these studies suggest that cachexia and xyloporosis should be concluded as the same disease. The group II citrus viroids are characterized by a very conservative genome since only a few base changes were detected after passaging through the four different families of plants known to be hosts of hop stunt viroid (HSVd). Five variants from naturally-infected grapevine have been found and determined to contain in 295-297 bases. One HSVd-gVl, was negative for cachexia symptoms on PSM, but induced mild symptoms on PSM, but induced mild symptoms on Mapo tangelo what might represent a more sensitive indexing host than PSM. Chimeric viroid cDNA clones carrying the C-V-T2 domain region from IIa-clone induced severe symptoms on luffa, while clones with a similar genome region from IIb-clone induced very strong cachexia symptoms on PSM. In site-directed mutated cDNA clones, the six mutagenic loci introduced into the V-domain of the IIa-clone were successful in the induction of pathogenicity on PSM. From this, the C-V-T2 domains of CVd-IIa and CVd-IIb represent an important locus for regulating pathogenicity on both luffa and PSM. Probe CX2 designated as a complementary to CVd-IIb at position 182-208 was demonstrated to function as a cachexia-specific probe. The sequence as contain in the probe CX2 was tested as a cachexia specific primer for RT-PCR as both a cDNA and hDNA. When the CX2 sequence was used as a hDNA primer, a cachexia-specific product resulted under specific conditions of 1.0 mM MgCl2 at 55C.

Biological sciences

Botany

Plant pathology

J. S. Semancik

K. Reanwarakorn

p

[Thesis]

276903

a

Y