Geminiviruses are plant DNA viruses that cause severe economic damage to tomato, cotton, corn, and other crop plants, primarily in tropical regions of the world. They are considered to be an emerging threat because of recent outbreaks that caused wide-spread famine in Uganda (cassava) and other parts of Africa (corn) and economic hardship in Pakistan and India (cotton). They are a threat to the US because of the recent introduction of Tomato yellow leaf curl virus from Israel and the possible introduction of Old World geminiviruses infecting cotton or corn. Although resistance genes for different geminiviruses have been identified in bean, tomato, corn, and other crops, none of them has been sequenced. Sequencing of a potyvirus resistance gene in Arabidopsis was a breakthrough for plant breeding because it allowed the identification of naturally occurring resistance genes in several different crop plants and also shed light on exactly which host factors were important for RNA virus infection. An Arabidopsis gene has been identified that confers resistance to two very different types of DNA virus. Such broad-based resistance would be an important complement to genetic engineering methods, such as RNAi, that are powerful but virus-specific.
The goal of this project is to identify and sequence the Arabidopsis geminivirus resistance gene by determining which DNA fragments correlate with resistance in a mapping (F2) population. A cloned gene corresponding to this DNA fragment will be transformed into a susceptible plant and challenged with both geminiviruses. If the gene behaves as expected (resistance is conferred), information about the new function of the gene will be submitted to the Arabidopsis Information Resource (TAIR) and then published. This project will support a Hispanic postdoctoral student for one year.
The goal of this proposal was to map and clone a geminivirus resistance gene in the model plant, Arabidopsis. Geminiviruses are DNA viruses that replicate inside of plant nuclei along with chromosomal DNA. No resistance gene for a geminivirus has ever been cloned in any species, although many have been mapped. It would be a breakthrough to be able to identify this resistance gene because then we could understand more about how geminiviruses interact with their host plants and what the possible weak links in this interaction are. Geminiviruses are an emerging group of plant viruses that are responsible for several devastating plant diseases in tropical and sub-tropical parts of the world. Low-pass genome sequencing was used to identify 96 different markers which are currently being used to associate particular regions of the DNA with resistance. Unfortunately, we were not able to complete the mapping down to the gene, but follow-up funding has been obtained to continue the work. During the course of this work, it was discovered that satellite DNA isolated from an entirely different species (cassava) was able to break the geminivirus resistance in Arabidopsis. This was quite exciting because these particular satellites have been responsible, along with Cassava brown streak virus, for the loss of much of the cassava harvest in food-insecure regions of Africa. Although the satellites have been sequenced, they do not contain normal-looking open reading frames and it is not clear how they work. If we can understand what kind of resistance gene they overcome, we can get a better idea of how they work.
