Biomedical subjects

J L Jeffrey

Publications and source records attributed to J L Jeffrey.

4 recordsLinked to original sources

PubMed2000

Bipartite geminivirus host adaptation determined cooperatively by coding and noncoding sequences of the genome.

Bipartite geminiviruses are small, plant-infecting viruses with genomes composed of circular, single-stranded DNA molecules, designated A and B. Although they are closely related genetically, individual bipartite geminiviruses frequently exhibit host-specific adaptation. Two such viruses are bean golden mosaic virus (BGMV) and tomato golden mosaic virus (TGMV), which are well adapted to common bean (Phaseolus vulgaris) and Nicotiana benthamiana, respectively. In previous studies, partial host adaptation was conferred on BGMV-based or TGMV-based hybrid viruses by separately exchanging open reading frames (ORFs) on DNA A or DNA B. Here we analyzed hybrid viruses in which all of the ORFs on both DNAs were exchanged except for AL1, which encodes a protein with strictly virus-specific activity. These hybrid viruses exhibited partial transfer of host-adapted phenotypes. In contrast, exchange of noncoding regions (NCRs) upstream from the AR1 and BR1 ORFs did not confer any host-specific gain of function on hybrid viruses. However, when the exchangeable ORFs and NCRs from TGMV were combined in a single BGMV-based hybrid virus, complete transfer of TGMV-like adaptation to N. benthamiana was achieved. Interestingly, the reciprocal TGMV-based hybrid virus displayed only partial gain of function in bean. This may be, in part, the result of defective virus-specific interactions between TGMV and BGMV sequences present in the hybrid, although a potential role in adaptation to bean for additional regions of the BGMV genome cannot be ruled out.

Adaptation, Physiological↗

PubMed1998

Genetic determinants of host-specificity in bipartite geminivirus DNA A components.

Geminiviruses are small, ssDNA-containing plant viruses. Bean golden mosaic virus (BGMV) and tomato golden mosaic virus (TGMV) have bipartite genomes, the components of which are designated A and B. Although they are closely related, BGMV and TGMV nevertheless exhibit distinct host-specific phenotypes, with BGMV being well adapted to beans and TGMV being well adapted to Nicotiana benthamiana. A previous study showed that the two open reading frames (ORFs) of DNA B only partially determine the host-adapted phenotypes of BGMV and TGMV. We have now investigated the contributions of A component ORFs to host adaptation. Co-inoculated TGMV DNA A enhances the accumulation of BGMV in N. benthamiana. Using mutant and hybrid TGMV A components, the determinant of this phenotype was mapped to a region encompassing the overlapping AL2 and AL3 ORFs (AL23). BGMV- and TGMV-based hybrid A components containing the heterologous AL23 region each displayed host-specific gain-of-function phenotypes, which indicates that these sequences contribute to host adaptation in both viruses. In N. benthamiana, al2 and al3 mutants of either virus can be complemented in trans by the heterologous A component, so adaptation of the AL23 region to this host is likely mediated through a virus nonspecific, trans-acting factor. In beans, however, co-inoculated BGMV A does not affect the accumulation of TGMV, and TGMV did not complement BGMV al2 or al3 mutants. Thus host-adaptation of the AL23 region may have a different mechanistic basis in beans than it does in N. benthamiana. Although our experiments did not reveal significant host adaptation of the coat protein, which is encoded by the AR1 ORF, a virus-specific effect on viral ssDNA accumulation was observed.

Capsid↗

PubMed1996

Genetic requirements for local and systemic movement of tomato golden mosaic virus in infected plants.

Tomato golden mosaic geminivirus (TGMV) has two DNA components, A and B. Replication of DNA A can be detected in inoculated leaves, but DNA B is additionally required for virus movement in planta. Using viral DNA accumulation as an indication of the number of infected cells, we show here that both the BL1 and BR1 genes are necessary for local TGMV movement. We also demonstrate that transient expression of BL1 and BR1 together allows wild-type TGMV DNA A to move systemically. When the transient movement assay was used to analyze various A component mutants, all were found to move locally in inoculated leaves, and only an ar1 (coat protein) mutant was unable to move systemically. In addition, we confirm that a TGMV al2 (AR1 and BR1 trans-activator) mutant has a defect in local movement which can be rescued by provision of exogenous BR1, but not BL1. Finally, we show that the ability of TGMV coat protein mutants to accumulate single-stranded (ss) DNA is dependent on BR1. These results provide experimental evidence obtained in planta which supports three predictions of published models for bipartite geminivirus movement: (i) BL1 and BR1 have distinct and essential roles in cell-to-cell movement as well as systemic movement; (ii) BR1 may interact with viral ssDNA in vivo; and (iii) AL2 is indirectly required for movement through its effect on BR1 expression. In addition, our data suggest that specific models of bipartite geminivirus systemic movement should accommodate a role for the coat protein.

DNA, Single-Stranded↗

PubMed1996

Host and viral factors determine the dispensability of coat protein for bipartite geminivirus systemic movement.

Geminiviruses have unique, twinned icosahedral particles which encapsidate circular single-stranded DNA. Their genomes are composed of either one or two DNA segments. Monopartite geminiviruses absolutely require a functional coat protein (CP) for infectivity, whereas bipartite geminivirus CP null mutants can infect plants systemically. However, we show here that a CP mutant of the bipartite tomato golden mosaic virus (TGMV), which can infect Nicotiana benthamiana systemically, is confined to the inoculated leaves of Nicotiana tabacum or Datura stramonium. We also show that a CP mutant of the related bean golden mosaic virus (BGMV), which can infect beans systemically, is confined to the inoculated leaves of N. benthamiana. In each case, the extent of viral DNA accumulation in inoculated leaves was unaffected by the absence of CP, which suggests that CP is required specifically for systemic movement. The dispensability of CP is correlated with the degree of virus-host adaptation. TGMV is well adapted to N. benthamiana and does not require CP to infect this host systemically, whereas BGMV is poorly adapted to N. benthamiana and requires CP. Analysis of TGMV-BGMV hybrid viruses revealed that the viral genetic background can also affect the dispensability of CP for systemic movement in N. benthamiana. Thus, bipartite geminivirus movement in planta can be resolved genetically into three components: (i) local, cell-to-cell movement, which does not require CP; (ii) CP-dependent systemic movement, which occurs in all hosts tested; and (iii) CP-independent systemic movement, which occurs in hosts to which a given virus is well adapted.

Capsid↗