Characterization of Short-range Reproductive Strategy in Cuscuta attenuata

Dr. Robert C. Benjamin, Molecular Biology, University of North Texas

Molecular Plant Microbe Interactions 9: 810-818 (1996)

Characterization of cauliflower mosaic virus (CaMV) resistance in virus-resistant ecotypes of Arabidopsis

Callaway A, Liu W, Andrianov V, Stenzler L, Zhao J, Wettlaufer S, Jayakumar P, Howell SH

Howell Lab, Boyce Thompson Institute, Cornell University, Ithaca, NY 14853, USA.

Two Arabidopsis ecotypes are resistant to systemic infection by cauliflower mosaic virus (CaMV), a plant para-retrovirus. Arabidopsis ecotype Enkheim-2 (En-2) is highly resistant to CaMV infection while Bla-14 is more weakly resistant. CaMV resistance in En-2 can be largely attributed to the action of a single semidominant gene called cauliflower mosaic virus resistance1 (CAR1), located at a locus on chromosome 1. Resistance in Bla-14 is tightly linked to CAR1 and may be due to a weak allele at the same locus or another gene in a gene cluster. A quantitative polymerase chain reaction assay in conjunction with replication- and movement-incompetent viral mutants was used to determine whether virus replication or movement is affected in the resistant ecotypes. The pattern of accumulation of the wild-type virus in the resistant ecotype, En-2, was similar to that of a movement-incompetent CaMV mutant, suggesting that CAR1 interferes with or fails to support CaMV movement. CaMV-inoculated En-2 plants do not show visible signs of a hypersensitive response. However, indicators of an induced defense response do appear in CaMV-infected En-2 plants, such as the activation of pathogenesis-related protein gene expression and the production of camalexin, an Arabidopsis phytoalexin. Defense responses induced chemically or by mutation in the susceptible ecotypes delayed and reduced the severity of a CaMV infection. These findings suggest that CAR1 acts either in the susceptible ecotype to support virus movement or in the resistant ecotype to signal a defense response.

Cornell University
Prof. Stephen Howell
Plant Molecular Biology

"Map-Based Cloning of an Aluminum Resistance Gene in Arabidopsis thaliana"

We are using map-based cloning to isolate an Arabidopsis gene that confers resistance to aluminum (Al3+). In acidic environment, aluminum becomes soluble and inhibits root growth. We are mapping the location of a mutation (alr104) that allows normal plant growth in aluminum-rich media. We employed DNA markers called CAPS markers to localize the gene tothe fourth of the five Arabidopsis chromosomes. Using more CAPS markers allows the closer mapping of alr104 on chromosome 4. Then creating new markers from known gene sequences anchored to specific YACs allows us to find markers closer to the gene.

The markers are used to amplify specific fragments of genomic DNA by PCR and find polymorphisms, or DNA banding differences, between nonresistant and resistant plants. The frequency of recombination between the marker and alr104 equals the distance from the gene, so that the closest marker has the lowest rate of recombination from the gene. Finding the closest DNA marker will in turn help us more accurately map and clone the gene from the genome. Knowledge of the gene's involvement in aluminum resistance may lead to applications for agriculture.

Molecular evolution of nitrate reductase in Shewanella putrefaciens

Dr. Eric Gaidos and Dr. Ken Nealson, Biology and Geology and Planetary Sciences, California Institute of Technology

Cloning Chimeric Alphaviruses Sindbis and Ross River Virus

Short project to help in cloning additional mutations into a Sindbis virus containing the E1, 6K, and 3' UTR regions of Ross River virus, in order to increase virus infectivity and study the interactions of the E1 and E2 proteins.

Dr. Kyong-Min Kim and Drs. James and Ellen Strauss, Biology, California Institute of Technology