Seminar: "Exceptions to the norm: identifying new sources of resistance against important virulence factors of Xanthomonas oryzae"

Dr. Alejandra I. Huerta, National Science Foundation Postdoctoral Research Fellow, Department of Bioagricultural Sciences and Pest Management, Colorado State University

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February 26, 2018, 3:35 PM - 4:30 PM

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Dr. Alejandra Huerta is a postdoctoral fellow in the Department of Bioagricultural Sciences and Pest Management at Colorado State University in Fort Collins, CO. Her long-term goal is to develop broad translational impacts for international agriculture and development by investigating the molecular mechanisms bacteria use to compete against other bacteria, the identification of new sources of plant disease resistance, and the characterization of plant susceptibility loci targeted by bacterial effectors. She is currently investigating mechanisms of resistance using Xanthomonas spp. and rice as a model system. Alejandra is passionate about agriculture, plant diseases, and STEM education. She received a Bachelors in Spanish and Portuguese from the University of California in Santa Barbara and a second Bachelor’s in Chemistry from the University of California in Santa Cruz prior to earning her doctoral degree in Plant Pathology from the University of Wisconsin-Madison. She is an NSF Graduate and Postdoctoral Research Fellow.

Bacterial blight (BB), caused by Xanthomonas oryzae pv. oryzae (Xoo), is the single most destructive bacterial disease of rice. The optimal agronomic practice to manage the disease is deployment of resistant varieties. However, effective and durable disease resistance for BB is a continuous challenge due to the pathogen’s evolution and adaptation on cultivated varieties.

Key to Xoo pathogenicity and virulence are Transcription Activator-Like (TAL) effectors, which activate expression of host susceptibility genes. TAL effectors contribute differently to a strain’s virulence, and some are essential to pathogen fitness, including TAL effector TAL7b. We hypothesize that effective and durable disease resistance is attainable by targeting important virulence factors in the bacterium.

To test this hypothesis, we first screened 330 advanced inbred lines of the indica Multi-Parent Advanced Generation Inter-Cross (MAGIC) population for resistance against Xoo strains PXO99A and PXO99A carrying the virulence factor TAL7b (+TAL7b). Transgressive segregation for resistance in the MAGIC lines was observed to both PXO99A and PXO99A +TAL7b, suggesting the presence of resistance loci for BB.

To identify these loci we combined phenotypic and genotypic data to conduct genome-wide association studies and interval mapping analysis. Thirteen-disease resistance QTL were identified, six specific to PXO99A +TAL7B and seven to PXO99A. The loci encompassed several known major known resistance genes to BB in addition to novel loci associated to only TAL7b. The top ranking predicted gene target for TAL7b correlated to a QTL on Chromosome 8.
Lastly, 14 MAGIC AILs with variant alleles in the resistance locus identified were screened to confirm the resistance phenotype on Chromosome 8. A subset of these lines showed a decrease in susceptibility to PXO99A +TAL7b compared to PXO99A. Altogether, our data suggest that the TAL7b target is a disease susceptibility gene that contributes to Xoo fitness in rice and that the resistance locus identified may harbor polymorphisms in the TAL7b gene target, disabling activation of the susceptibility gene. These results highlight the importance characterizing susceptibility genes to facilitate development of more durable disease resistant rice varieties.

Dr. Alejandra Huerta will also be speaking at the INTAD Global Gallery on Friday February 23 from 10:30-11am - Dr. Alejandra Huerta will discuss her internationally focused career, including experiences in Bangladesh as a U.S Borlaug Fellow in Global Food Security.

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