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Archives - S7-05
Resistance to African Cassava Mosaic Disease Conferred by Wildtype
and Spontaneous Mutated Versions of the Replication-Associated
Protein (AC1) from a Kenyan Isolate of African Cassava Mosaic Virus
Chellappan P., M.V. Masona, N.J. Taylor, J.Pita,
J.Yadav, and C.M. Fauquet
International Laboratory for Tropical Agricultural Biotechnology (ILTAB),
Danforth Plant Science Center, 975 Warson Road, St Louis, MO 63132
iltab@danforthcenter.org
African cassava mosaic virus (ACMV), the causal agent of cassava
mosaic disease in Africa, is a whitefly–transmitted, bipartite
geminivirus. Friable embryogenic calli of cassava were genetically
transformed by particle bombardment with the replicase (AC1) gene of
an ACMV-Kenyan isolate with the objective to employ a pathogen
derived resistance strategy against ACMV. Sequence analysis of the
paromomycin resistant calli recovered showed that in addition to
insertion of the wild type AC1 gene, the occurrence of spontaneous
mutations, truncations and deletions were common within the
transgene and promoter sequences. In particular a point mutation was
seen, converting tyrosine to serine at the 238 amino acid position.
Plants were regenerated from this, the wildtype AC1 and other
transgenic calli. Presence of the transgenes were confirmed by
Southern blotting, while gene expression was analysed by RT-PCR and
Northern hybridization. Five wild type AC1 transgenic plant lines
and thirteen spontaneous mutated AC1 transgenic plant lines have
been challenged with infectious viral clones of ACMV and East
African cassava mosaic virus. To date, most transgenic plant lines
have displayed delayed symptoms while in four remained symptom-free
21 days after challenging. Presence and accumulation of the virus is
being assessed in systemic leaves by PRC and Southern dot blotting.
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