Keri Wang's Research Interests

Plants and pathogens have evolved for their survival by developing defense and counter defense systems respectively. Traditionally, the plant disease resistance is referred as host resistance in which the plant species is the host of the pathogen, i.e. a plant species which can be infected by a pathogen in nature. In the past two decades, significant research progress in mechanisms of pathogenicity and plant resistance has been made due to the developments in genomic technologies and sequencing of plant and microbe genomes. Many elicitors in pathogens and resistance signaling pathway components in plants have been identified and characterized. However, the mechanism of nonhost resistance in which a pathogen cannot infect a particular plant species in nature is poorly understood. Plants are exposed to a numerous number of potential pathogens in nature. Nonhost resistance is the most common form of plant resistance since only a limited number of potential pathogens can induce diseases in a given plant species. I am interested in identifying the signal transduction components involved in nonhost resistance which will lead to better understanding of nonhost resistance mechanism in plants.

• Use of virus-induced gene silencing (VIGS) system as a fast-forward genetics approach to identify genes involved in nonhost resistance

VIGS provides a powerful high throughput tool to investigate functional genomics since it allows us to study a specific gene or a gene family rapidly without requiring plant transformation. The interested genes or cDNA clones from a cDNA library can be directly cloned into a VIGS vector and used for silencing to screen for interesting phenotypes. We use Nicotiana benthamiana as a model plant to identify the signal components involved in resistance to nonhost pathogens, Pseudomonas syringae pv. glycinea (type I) and P. syringae pv. tomato (type II), by silencing 3,000 cDNA clones from a normalized N. benthamiana cDNA library using VIGS system. Currently, my research focus on characterizing four candidate genes, identified by forward genetics, involved in nonhost resistance. Disease symptoms are developed or hypersensitive reactions (HR) is delayed on the leaves of silenced N. benthamiana challenged with P. syringae pv. glycinea or P. syringae pv. tomato respectively. The population of these nonhost pathogens in plants silenced with each candidate gene was 100-folder greater than the control at 3 days after inoculation with low bacterial concentration (104 cfu/ml). I have cloned the full length gene sequence of these candidate genes. The functions of these genes are being further characterized by application of RNA interference (RNAi) in N. benthamiana and also by characterizing the T-DNA mutants of Arabidopsis thaliana.

A gene silenced (left) and wild-type (right) N. benthamiana inoculated with P. syringae pv. glycinea

• Use of green fluorescent protein to study plant-pathogen interactions

Green fluorescent protein (GFP), originally isolated from jellyfish Aequorea victoria, has been extensively used as a marker gene in microbiology and cell biology in both prokaryotes and eukaryotes due to its species independence and its lack of requirement for any substrates or cofactors, enabling detection by nondestructive means. We have constructed a broad host range plasmid vector that can express GFP and transformed it into several different bacterial strains. We use GFP to label pathogens to study why a plant can be infected by a nonhost pathogen after a gene required for nonhost resistance is silenced. This will help us to better understand the mechanism of nonhost resistance.

SGT1 silenced N. benthamiana inoculated with a nonhost pathogen, P. syringae pv. tomato labeled with GFP.