Dr. Kushalappa is a Plant Pathologist. His current research focus is to identify plant biotic stress resistance genes through forward and reverse genetics, and use these genes/alleles to replace the susceptible genes/alleles in elite or new cultivars, based on cisgenetic engineering (gene transfer between sexually compatible plants), using CRISPR-Cas9 systems, to increase the genetic diversity of crop plants.
Plants defend against pathogen attack using biochemicals that are constitutively produced or induced following pathogen invasion. Based on non-targeted metabolomics and proteomics using liquid chromatography and high resolution mass spectrometry (LC-ESI-LTQ-Orbitrap) we have detected thousands of metabolites and proteins in wheat/barley – Fusarium graminearum (fusarium head blight) and potato-Phytophthora infestans (late blight) interaction systems. The resistance related (RR) metabolites were linked in their metabolic pathways to explore their precursors and possible polymers or structural components that explained the mechanisms of resistance. Several of these biochemicals are known antimicrobials, toxin inhibitors/detoxifiers, and cell wall thickening compounds. The proteins identified were mainly enzymes catalyzing these metabolites or pathogenesis related proteins. Metabolic pathway regulation by signaling molecules, hormones and transcription factors also have been identified. The metabolites with high fold change in abundance in resistant genotypes than in susceptible (RR metabolites) were searched in genomic databases to identify candidate genes. The putative resistance genes were sequenced to identify the SNPs and the gene expressions were used to confirm the association of these genes with metabolites. The candidate genes were then silenced (VIGS) in resistant and susceptible genotypes to validate gene functions.
Our current research activities are: i) Identification of RR genes in quantitative trait loci (QTL) of near isogenic wheat lines, and in other genotypes of wheat, barley and potato against biotic stress; ii) mapping of upstream signaling and regulatory genes associated with RR genes responsible for cell wall enforcement and other resistance functions; iii) use these sets of regulatory and RR genes/alleles to replace susceptible genes/alleles in elite cultivars through cisgenetic engineering, using CRISPR-Cas9 systems. Cisgenic plants with high levels of resistance to late blight in potato and to fusarium head blight in wheat and barley will be evaluated under field conditions in collaboration with producers in Colombia and Canada.
Gunnaiah R and Kushalappa AC. 2014. Metabolomics deciphers the host resistance mechanisms in wheat cultivar Sumai-3, against trichothecene producing and non-producing isolates of Fusarium graminearum. Plant Physiology and Biochemistry (accepted).
Yogendra KN, Pushpa D, Mosa K, Kushalappa AC, Murphy A and Mosquera T. 2014. Quantitative resistance in potato leaves to late blight associated with induced hydroxycinnamic acid amides. Functional and Integrative Genomics. 14:285–298.
Pushpa D, Yogendra K, Gunnaiah R, Kushalappa AC and Murphy A. 2014. Identification of late blight resistance related metabolites and genes in potato through non-targeted metabolomics. Plant Molecular Biology Reporter. 32:584-595.
Chamarthi S, Kundan K, Gunnaiah R, Kushalappa AC, Dion Y, Choo TM. 2014. Identification of fusarium head blight resistance related metabolites specific to doubled-haploid lines in barley. European J. Plant Pathology. 138: 67-78.
Kushalappa AC and Gunnaiah R. 2013. Metabolo-proteomics to discover plant biotic stress resistance genes. INVITED REVIEW: Trends in Plant Science. 18: 522-531.
Gunnaiah R, Kushalappa AC, Duggavathi R, Fox S and Somers DJ. 2012. Integrated Metabolo-proteomic approach to decipher the mechanisms by which wheat QTL (Fhb1) contributes to resistance against Fusarium graminearum. PLoS ONE 7:e40695.
Kumaraswamy GK, Kushalappa AC, Choo TM, Dion Y. and Rioux S. 2012. Differential metabolic response of barley genotypes, varying in resistance, to trichothecene-producing and nonproducing (tri5-) isolates of Fusarium graminearum. Plant Pathology 61, 509–521.
Bollina V, and Kushalappa AC. 2011. In vitro inhibition of trichothecene biosynthesis in Fusarium graminearum by resistance-related endogenous metabolites identified in barley. Mycology 2:291-296.
Bollina V, Kushalappa AC, Choo TM, Dion Y and Rioux S. 2011. Identification of metabolites related to mechanisms of resistance in barley against Fusarium graminearum, based on mass spectrometry. Plant Molecular Biology. 77:355-370.
Kumaraswamy GK, Kushalappa AC, Choo TM, Dion Y. and Rioux S. 2011. Mass spectrometry based metabolomics to identify potential biomarkers for resistance in barley against fusarium head blight (Fusarium graminearum). Journal of Chemical Ecology 37:846-856.
Kumaraswamy GK, Bollina V, Kushalappa AC, Choo TM, Dion Y., Rioux S., and Faubert D. 2011. Metabolomics technology to phenotype resistance in barley against Gibberella zeae.. European J. Plant Pathology 130:29-43.
Bollina, V., Kumaraswamy, KG., Kushalappa, AC., Choo TM., Dion Y., Rioux S., Faubert D. and Hamzehzarghani H. 2010. Mass spectrometry based metabolomics application to identify quantitative resistance related metabolites in barley against fusarium head blight. Molecular Plant Pathology 11:769-782.
Kushalappa, AC., Vikram, A. and Raghavan, GSV. 2008. Metabolomics of headspace gas for diagnosing diseases of fruits and vegetables after harvest. Stewart Posthar. Tech. 4:1-7.
Paranidharan, V., Abu-Nada, Y., Hamzehzarghani, H., Kushalappa, A. C., Dion, Y., Rioux, S., and Comeau, A. 2008. Resistance related metabolites in wheat against Fusarium graminearum and the virulence factor, DON. Botany 86: 1168-1179.
Hamzehzarghani, H., Paranidharan, V., Abu-Nada, Y., Kushalappa, A. C., Dion, Y., Rioux, S., Comeau, A. Yaylayan, V. and Marshall, W. D. 2008. Development of metabolic profiling technology for potential high throughput screening of quantitative resistance in wheat cultivars against fusarium head blight. Can. J. Plant Path. 30:24-36.
Abu-Nada, Y., Kushalappa, A. C., Marshall, W., Yaylayan, V., Al-Mughrabi, K. and Murphy, A. 2007. Temporal dynamics of pathogenesis related metabolites and their plausible pathways of induction in potato leaves following inoculation with Phytophthora infestans. European J. Plant Path. 118:375-391.