Manipulation of Host Signaling by Pathogens
Somerville, Shauna .
The Plant Cell: The First Line of Defense.
A majority of host plants are resistant to the majority of pathogens in their environment. The underlying mechanisms of this form of disease resistance are poorly studied. Our lab, together with P. Schulze-Lefert and H. Thordal-Christensen, identified mutants of the model plant Arabidopsis thaliana that were compromised in their resistance to the powdery mildew fungus, Blumeria graminis f. sp. hordei, which is pathogenic only on barley. Several genes not previously implicated in resistance were identified by this approach, including PEN1 (=SYP121) a syntaxin and functional homologue of the barley ROR2 gene; PEN2, a glycosyl hydrolase; and PEN3 (=PDR8), an ABC transporter. The plasma membrane-localized ROR2, PEN1 and PEN3 proteins accumulate locally at penetration sites in inoculated plant tissues, as does the barley MLO protein, which suppresses penetration resistance. These observations suggest that plants mount effective, broad spectrum defenses designed to block pathogen entry into cells.
Host components that contribute to pathogen growth and disease development are largely unknown. To identify some of the components that support growth and development of the Arabidopsis powdery mildew, Golovinomyces cichoracearum, a screen for loss-of-susceptibility Arabidopsis mutants was initiated. Three of six mutants recovered from this screen affect some component of the host cell wall composition and the fourth mutant, pmr2 (=mlo2) is defective in the homologue of the barley MLO gene.
These two projects suggest that, over evolutionary time, virulent powdery mildew species must have acquired both the ability to conquer cell wall defenses and the ability to across cell walls without alarming their hosts.
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1 - Carnegie Institute, Plant Biology, Stanford, CA, 94305, USA
plant pathogen interaction
Presentation Type: ASPB Major Symposium
Location: International Ballroom/Hilton
Date: Tuesday, July 10th, 2007
Time: 11:15 AM