|Miklas, Phillip - Phil|
Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/19/2005
Publication Date: 6/1/2005
Citation: Larsen, R.C., Miklas, P.N., Druffel, K., Wyatt, S.D. 2005. NL-3K strain is a stable and naturally occurring interspecific recombinant derived from bean common mosaic necrosis virus and bean common mosaic virus. Phytopathology. Vol. 95(9):1037-1042.
Interpretive Summary: Bean common mosaic virus (BCMV) and Bean common mosaic necrosis virus (BCMNV) can cause major losses in bean production worldwide. Although not serologically related, the viruses are economically important in Africa, Europe, Asia and the Americas. All strains of BCMV and BCMNV are seed transmitted and are vectored by aphids in a non-persistent manner. Recently, a more virulent strain of the common NL-3 D strain was discovered in Kimberly, Idaho, and designated NL-3 K. Symptoms of severe mosaic, stunting, and plant death occurred from infection with NL-3 K compared to milder symptoms caused by NL-3 D. Serological tests by ELISA indicated that NL-3 K was not a mixed infection with any other strain of virus. After RNA sequencing of the entire virus genome, we found that the first 114 amino acids NL-3 K were 98% identical with the Russian strain (RU1) of BCMV. The remaining 3186 amino acids of NL-3 K were then 99% identical with NL-3 D. We also discovered that the genome length of NL-3 K was 293 nucleotides longer than NL-3 D. Most significantly, results show new evidence that a region of the virus, the P1 protein, is directly involved with symptom expression in bean plants. These findings are clear evidence of a recombination of two different viruses occurring naturally in the environment and provide important information on the continuing evolution of viruses infecting bean and other crops.
Technical Abstract: A strain of Bean common mosaic necrosis virus from Idaho was identified by ELISA using monoclonal antibodies and by differential dry bean host range studies to be similar to the NL-3 D strain of Drifjhout. However, the strain (NL-3 K) caused earlier and more severe symptoms on bean plants representing Host Groups 0, 4 and 5. The polyprotein of NL-3 K was 9889 nucleotides in length corresponding to a molecular size of 362.1 kDa compared to a 9626 nucleotide, 350.9 kDA polyprotein for NL-3 D. Sequence analysis of the putative P1 protein revealed the NL-3 K strain to be a recombinant between NL-3 D and the Russian strain (RU1) of Bean common mosaic virus. The first 114 predicted amino acids of the NL-3 K P1 region were 98% identical with RU1. The remaining 301 amino acids of the protein shared only 34% identity with RU1 but were 98% identical with NL-3 D. Primers designed flanking the recombination point in the P1 protein of NL-3 K produced an amplicon of the expected size using RT-PCR from total nucleic acid extracts of bean plants inoculated with NL-3 K, but not those with NL-3 D or RU1. The observed increased symptom severity on selected common bean hosts induced by NL-3 K suggests that the P1 region may play a significant role in pathogenicity and virulence.