Submitted to: Molecular Plant Microbe Interactions
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 9, 1997
Publication Date: N/A
Interpretive Summary: The identification of a single gene of pea seed-borne mosaic potyvirus (PSbMV) that is responsible for the ability to infect a line of peas is described. We used two strains of the virus that differ in their ability to infect a pea line (269818). PSbMV strain P1 can not infect this pea whereas strain P4 does infect this line of pea. By swapping genes between two strains of PSbMV it was shown that the VPg, one of the virus genes thought to be involved in virus replication and is also attached to the 5¿ end of the viral RNA, controls virulence on this pea line. When the VPg of strain P1 is inserted into strain P4, P4 is no longer able to infect the peas. Also, in all cases where the VPg of P4 was inserted into P1, P1 was able to infect the peas. This is the first case where a viral gene has been shown to interact specifically with a recessive plant gene for resistance. This work opens the door for identifying the host gene responsible for virus resistance.
Technical Abstract: The mechanism of Pisum stivum pathotype-specific resistance to pea seedborne mosaic potyvirus (PSbMV) was investigated and the coding region determinant of PSbMV virulence was defined. Homozygous recessive sbm-1 peas are unable to support replication of PSbMV pathotype 1 (P-1), whereas, biochemically and serologically related pathotype 4 (P-4) is fully infectious in the sbm-1/sbm-1 genotype. We were unable to detect viral coat protein or RNA using DAS-ELISA and RT-PCR to assay sbm-1/sbm-1 P- 1-inoculated protoplasts and plants. Lack of viral coat protein or RNA in P-1 transfected sbm-1/sbm-1 protoplasts, suggest that sbm-1 resistance is occuring at the cellular level and that inhibition of cell-to-cell virus movement is not the operating form of resistance. In addition, because virus products were not detected at any time post-inoculation, resistance must either be constitutive or expressed very early in the virus infection process. P-1 resistant peas challenged with full-length infectious P-1/P-4 recombinant clones demonstrated that a specific P-4 coding region, the 21 kDa genome linked protein (VPg), was capable of overcoming sbm-1 resistance, whereas clones containing the P-1 VPg coding region were non-infectious to sbm- 1/sbm-1 peas. VPg is believed to be involved in potyvirus replication and its identification as the PSbMV determinant of infectivity in sbm-1/sbm-1 peas is consistent with disruption of an early P-1 replication event.