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Name: Hari Karki
Current Position: Molecular breeder (tomato) at Lipman Family Farms, Florida, USA
Education: M.S. and Ph.D. degrees in plant health at Louisiana State University, Baton Rouge, LA, USA
Brief Bio: Over the years, I have conducted research in the field of plant pathology, genetics, genomics, and molecular biology at Louisiana State University (LSU), The Sainsbury Laboratory (TSL) and U.S. Department of Agriculture (USDA). I was always attracted to different aspects of agriculture, which eventually led to my enrollment at the agriculture institute of Nepal. After completion of my undergraduate degree, I joined the Department of Plant Pathology and Crop Physiology at LSU to pursue a master's degree, studying the bacterial pathogen
Burkholderia glumae. After completion of a M.S. degree in plant health, I continued studying for a Ph.D. degree and worked on understanding the virulence mechanism and population diversities of
B. glumae through targeted sequencing and mutagenesis of pathogenic and nonpathogenic isolates. At TSL, I worked on a capture-based next-generation sequencing method, resistant gene enrichment and sequencing (RenSeq), and gene enrichment and sequencing (GenSeq) to map and clone resistance genes against late blight of potato caused by
Phytophthora infestans. At the USDA, I worked on the molecular dissection of
RB (also known as
Rpi-blb1) mediated late blight resistance in potato.
RB is a broad-spectrum late blight resistance gene cloned from
Solanum bulbocastanum, which recognizes
P. infestans effector IPI-O (in planta–induced gene O), also known as
Avrblb1. IPI-O is a multigene effector family that has been divided into three major classes. IPI-O class I and class II variants detect
RB and initiate resistance activation; however, with class III variants, IPI-O4 not only escapes recognition by
RB but is also capable of inhibiting the hypersensitive response (HR) by directly binding the
RB CC domain. To identify the
RB CC domain that does not interact with IPI-O4, we explored natural variations in the
RB CC domain from different Solanaceae species and identified the
RB CC domain from
S. pinnatisectum (pnt) that does not interact directly with IPI-O4. We identified crucial amino acids in the
RB CC domain that play an important role in the avoidance of suppression activity of IPI-O4 and, thus, could enable resistance activation even in the presence of this suppressor. We further modified these amino acids in a wild-type
RB gene and concluded that modification of single amino acids within the
RB CC domain can either diminish or increase the resistance capability of the
RB gene. Our study provides a clue about engineering new variants of known
R genes that can further expand the resistance spectrum.
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