Plant NB-LRR function
One branch of the plant immune system is based on the recognition of proteins associated with specific pathogens. This recognition is mediated by cytoplasmic NB-LRR proteins; so named for the presence of nucleotide-binding and leucine-rich repeat domains. Plant genomes encode hundreds of highly variable NB-LRR–encoding genes, each with the ability to recognize specific pathogen-encoded proteins. We investigate both intra- and inter-molecular protein-protein interactions involving NB-LRR proteins as well as investigating the mechanisms induced by NB-LRR signaling that ultimately curtail pathogen accumulation.
Plant-virus interactions
RNA silencing and antivirus resistance
Eukaryotes possess protein complexes that recognize dsRNA and process it into small fragments. These small RNAs in turn target homologous single-stranded RNA in a variety of ways, in conjunction with a family of ribonucleases known as Argonaute proteins. Argonaute proteins are involved in a number of mechanisms that regulate gene expression, collectively referred to as RNA silencing or RNA interference (RNAi). At the same time, RNA silencing is used by plant cells as a defence against viruses by recognizing their dsRNA replication intermediates and targeting them for degradation and/or translational repression. Our research in this area is aimed at understanding which (of the many) RNAi components in plants are involved in anti-viral defence, how these components target virus RNA and how viruses, in turn, have evolved to inhibit RNAi mechanisms.
Additionally, we have shown that once an NB-LRR protein is activated, translation of viral RNA transcripts is inhibited. We have shown that this response requires members of the Argonaute family, different from those that mediate other RNA silencing mechanisms. Our research is aimed at better understanding how Argonaute proteins control viral infections by regulating virus gene expression as well as regulating cellular transcripts.
Translation control and defense signaling
We have shown that upon induction of an NB-LRR defence response that viral RNAs are subjected to translational repression. Although this repression is relatively specific to viral transcripts, using next-gen sequencing and ribosome purification, we find that certain cellular mRNAs are likewise regulated. We are working to verify a number of target genes subject to translational control and to understand how this control is brought about by signaling pathways in the cell.
Eukaryotes possess protein complexes that recognize dsRNA and process it into small fragments. These small RNAs in turn target homologous single-stranded RNA in a variety of ways, in conjunction with a family of ribonucleases known as Argonaute proteins. Argonaute proteins are involved in a number of mechanisms that regulate gene expression, collectively referred to as RNA silencing or RNA interference (RNAi). At the same time, RNA silencing is used by plant cells as a defence against viruses by recognizing their dsRNA replication intermediates and targeting them for degradation and/or translational repression. Our research in this area is aimed at understanding which (of the many) RNAi components in plants are involved in anti-viral defence, how these components target virus RNA and how viruses, in turn, have evolved to inhibit RNAi mechanisms.
Additionally, we have shown that once an NB-LRR protein is activated, translation of viral RNA transcripts is inhibited. We have shown that this response requires members of the Argonaute family, different from those that mediate other RNA silencing mechanisms. Our research is aimed at better understanding how Argonaute proteins control viral infections by regulating virus gene expression as well as regulating cellular transcripts.
Translation control and defense signaling
We have shown that upon induction of an NB-LRR defence response that viral RNAs are subjected to translational repression. Although this repression is relatively specific to viral transcripts, using next-gen sequencing and ribosome purification, we find that certain cellular mRNAs are likewise regulated. We are working to verify a number of target genes subject to translational control and to understand how this control is brought about by signaling pathways in the cell.
Improving a plant vaccine platform through modulation of the plant defence system
Vaccine production platforms based on transient expression of antigens in plants using Agrobacterium tumefaciens allow for efficient production of subunit vaccines that can be rapidly scaled up. However, plants react to Agrobacterium with an antimicrobial defense response which can decrease protein production and quality. We are characterizing the plant immune response against Agrobacterium, with the ultimate goal of attenuating plant defense responses an improving protein expression.
Plant-viroid Interactions
Viroids are the simplest infectious agents known, consisting of small circular RNA molecules of less than 300 nucleotides. These RNA molecules encode no proteins encode no known proteins, yet are able to commandeer the plant cell machinery for their own replication. Viroids cause disease in a number of economically important crop and horticultural plants, but often show a high degree of host specificity. In collaboration with the Perreault lab, we are studying how viroids interact with, or are able to avoid, the host RNAi machinery (see above). In addition, we are using natural variation to identify and understand the role of host factors in viroid replication and host specificity.
Viroids are the simplest infectious agents known, consisting of small circular RNA molecules of less than 300 nucleotides. These RNA molecules encode no proteins encode no known proteins, yet are able to commandeer the plant cell machinery for their own replication. Viroids cause disease in a number of economically important crop and horticultural plants, but often show a high degree of host specificity. In collaboration with the Perreault lab, we are studying how viroids interact with, or are able to avoid, the host RNAi machinery (see above). In addition, we are using natural variation to identify and understand the role of host factors in viroid replication and host specificity.