Point substitution in a promoter-like region and the V1 gene affect the host range and symptoms of maize streak virus.
The nucleotide sequences of full-length infectious clones of two symptomatic and host range variants (MSV-Ns and MSV-Nm) of the Nigerian strain of maize streak virus (MSV) have been determined and shown to differ by only three nucleotides. MSV-Ns produced symptoms in infected maize plants sooner and the streaks were wider and more chlorotic than those of MSV-Nm; variant MSV-Ns also had a wider host range within the Gramineae. None of the three nucleotide differences resulted in amino acid changes. Site-directed mutagenesis showed that a substitution at nucleotide (nt) 40 in the V1 gene affected streak width, while severity of chlorosis, length of streaks, latency, and host range was determined by a single base change at nt 2473 in the large intergenic region. The nt 2473 change altered a potential promoter sequence (TATA box) in MSV-Ns 101 nucleotides upstream of the initiation codon of the C1 gene. Mutagenesis of TATA sequences located downstream of TATA -101 showed that TATA -101 alone was sufficient to confer a wide host range phenotype on MSV-Ns and suggested that it might function as a promoter for the expression of complementary-sense open reading frames. When compared with an updated promoter consensus derived from genes of the Gramineae, the promoter context around TATA -101 in MSV-Ns was not more favorable than those found at -57 and -62 in MSV-Nm.
Boulton
M I
MI
John Innes Institute, John Innes Centre for Plant Science Research, Norwich, United Kingdom.
King
D I
DI
Donson
J
J
Davies
J W
JW
D001483:Base Sequence; D004279:DNA, Viral / Q000737:chemistry; D005814:Genes, Viral; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D016366:Open Reading Frames; D010935:Plant Diseases; D010942:Plant Viruses / Q000235:genetics*; D011401:Promoter Regions, Genetic; D016385:TATA Box; D003313:Zea mays / Q000382:microbiology*
D004279:DNA, Viral