Population Diversity and in Planta Movement of Clavibacter Michiganensis Subsp. Michiganensis PDF Download

Author: Matthew Tancos
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Languages : en
Pages : 308

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Book Description
The Gram-positive bacterium Clavibacter michiganensis subsp. michiganensis is the causal agent of bacterial canker of tomato, and an economically devastating seed-borne pathogen that inflicts considerable damage throughout all major tomato producing regions. Within New York, annual outbreaks are a common occurrence since C. michiganensis subsp. michiganensis is easily spread by infected transplants, improper sanitation, and/or contaminated seed. In order to better characterize the pathogen and its interactions with tomato, my research focused on population diversity and the in planta movement of C. michiganensis subsp. michiganensis, with an emphasis on virulence and modes of infection. The first chapter explores the diversity of the C. michiganensis subsp. michiganensis New York population. Over an eleven year period, 51 field isolates were collected from independent outbreaks throughout New York and characterized with both repetitive element-PCR and multilocus sequence analysis. Our research identified a highly diverse New York C. michiganensis subsp. michiganensis population. Several of the isolates were reoccurring strains, but many were novel and appeared on farms with no previous history of bacterial canker of tomato, suggesting recent introduction events from infected seed or transplants. The second chapter investigates the routes of seed infection by using a constitutively eGFP-expressing virulent C. michiganensis subsp. michiganensis isolate (GCMM-22) to demonstrate that C. michiganensis subsp. michiganensis does not only access seeds systemically through the xylem, but also externally through tomato fruit lesions, which harbor high intra-and intercellular populations. C. michiganensis subsp. michiganensis was observed within the developing seed, endosperm, and funiculus, although at relatively low levels compared to the large number of cells observed in the xylem and pericarp cells. Chapter 3 characterizes the i putative plant-like expansin gene, CmEXLX2, in order to elucidate its role in disease development. Disruption of CmEXLX2 in C. michiganensis subsp. michiganensis resulted in significant increases in necrosis, atypical lesion proliferation, and symptom development on tomato, compared to the wild-type and complemented strains. No differences in growth were observed in vitro between strains, but larger in planta mutant populations appeared to be directly associated with increased disease severity. We hypothesize that increased necrosis within the nutrient-poor xylem may result in increased nutrient availability, yielding larger in planta mutant populations and magnifying symptom progression. Finally, included in the appendix is a preliminary molecular study investigating the role of a putative [beta]-N-acetylglucosaminidase (nagA) in C. michiganensis subsp. michiganensis infections. Proteomic studies demonstrated that [beta]-N-acetylglucosaminidase was the third most upregulated protein under infectionmimicking conditions, but its role in infection remains unknown. Disruption of nagA resulted in the reduction of bacterial attachment in vitro when grown in tomato sap.