Xanthomonas oryzae pathovars: model pathogens of a model crop – Bogdanove laboratory
Research in the Bogdanove laboratory
Bacterial diseases cause significant losses in many crops, and control measures are often limited or unavailable. Also, bacterial diseases of plants can be tractable models for understanding plant responses to microbial pathogens generally. Research in the Bogdanove laboratory centers on two important diseases of rice, bacterial blight and bacterial leaf streak. Blight and leaf streak are caused by different pathovars of the same bacterial species, Xanthomonas oryzae. Because of this and because rice is a world-wide staple as well as a model for cereal biology, the two diseases constitute a uniquely important system for understanding the pathogen and host traits that allow microbes to exploit different plant tissues. Our long-term goal is to generate knowledge and tools useful in interfering with disease and in enhancing natural plant defense for better disease control.
Bacterial blight and bacterial leaf streak of rice
Bacterial blight and bacterial leaf streak of rice are economically important diseases in many rice-growing regions of the world and are representative of the two major types of disease caused by Gram-negative pathogens in plants. Bacterial blight is caused by X. oryzae pathovar oryzae, which enters through wounds or water pores (hydathodes) in the leaf and travels systemically through the plant xylem. Bacterial leaf streak is caused by X. oryzae pv. oryzicola, which typically enters through stomata and colonizes the intercellular spaces of the leaf photosynthetic tissue.
Functional genomics of rice susceptibility to bacterial blight and bacteria leaf streak.
To better understand rice susceptibility to the two pathogens we are using genomic and proteomic approaches, alongside molecular biology, genetics, cell biology and biochemistry. We discovered that X. oryzae pv. oryzicola actively inhibits rice defense by injecting specific proteins into rice cells via the via type III secretion system (Makino et al. 2006, Mol. Plant-Microbe Interact.19:240-249). By transcript profiling using the Affymetrix rice GeneChip®, we discovered that X. oryzae pv. oryzae and X. oryzae pv. oryzicola genetically reprogram their host for susceptibility in different ways. One appears largely to target specific transcription factors and genes with putative roles in reproduction and development, whereas the other likely modulates defense signaling and other pathways by affecting genes that govern redox status (Niño-Liu et al, in preparation).
Comparative genomics of xanthomonad pathogens to understanding vascular and non-vascular bacterial diseases of dicots and monocots.
To identify key bacterial determinants of host- and tissue-specific pathogenesis, we are carrying out comparative and functional genomic analyses of the two X. oryzae pathovars, as well as X. campestris pv. campestris and X. campestris pv. armoraciae, vascular and non-vascular counterparts that infect the dicot model plant Arabidopsis. In collaboration with The Institute for Genome Research, and colleagues at The University of Maryland, Kansas State University, and Colorado State University, we have sequenced and annotated three new Xanthomnas genomes, now available through the Comprehensive Microbial Resource (www.tigr.org/CMR). These new data are enabling research that provides insight into the ancestral Xanthomonas genome and evolution of pathogenic traits. It is also facilitating gene discovery and cross-species characterization of genes important in host interactions.