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Abstract Detail


Plant-Pathogen Interactions

Ma, Wei [1], Ali, Rashid [1], Lemtiri-Chlieh, Fouad [1], Smigel, Andries [1], Berkowitz, Gerald [2].

cAMP acts as an early signal upstream from Ca2+ in plant pathogen perception signaling cascades.

A rise in plant cell cytosolic Ca is an early step in pathogen perception and subsequent nitric oxide (NO)-mediated signaling cascades leading to plant innate immunity and hypersensitive response (HR). It is not yet clear how pathogen perception by plant cells is translated into a cytosolic Ca rise. Arabidopsis dnd1 mutant plants lacking the plant cell membrane cyclic nucleotide gated channel CNGC2 lack a cAMP-activated inward Ca current, pathogen associated molecular pattern (PAMP) elicitor-induced NO generation, and HR to P. syringae tomato (Pst). Here, we also show results consistent with a critical step upstream from inward Ca current as involving pathogen-induced rise in cAMP. The PAMP lipopolysaccharide (LPS) induces NO generation in guard cells of wild type but not dnd1 epidermal peels. Plant cell cytosolic cAMP level is controlled by the integrated activities of adenylate cyclase (AC) (cAMP synthesis) and cAMP-phosphodiesterase (PDE) (cAMP breakdown). The AC inhibitor dideoxyadenosine (DDA) prevented LPS-induced NO rise. In the absence of LPS, addition of either cAMP or the PDE inhibitor IBMX induced NO generation. Calmodulin blocks cAMP activation of CNGC2 Ca current. Patch clamp analysis indicated that in the presence of a calmodulin antagonist, LPS activates inward Ca currents in guard cells; this result links pathogen perception to the activation of the Ca channel. In plants inoculated with avirulent Pst, addition of IBMX (causing a rise in ambient cAMP) led to faster HR while reducing ambient cAMP with DDA prevented HR. Innate immunity in animals is mediated by PAMP-induced changes in AC and/or PDE. Our work suggests that pathogen-induced modulation of these enzymes may begin a signaling cascade (involving Ca and NO) leading to plant innate immunity as well.


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1 - University of Connecticut, Department of Plant Science, Agriculture Biotectnology Laboratory, 1390 Storrs Rd., U-4163, Storrs, Connecticut, 06269, USA
2 - University of Connecticut, Department of Plant Science, Agriculture Biotectnology Laboratory, 1390 Storrs Rd., U-4163, Storrs, Connecticut, 06269-4163, USA

Keywords:
hypersensitive response
Calcium
cAMP
ion channel.

Presentation Type: Plant Biology Abstract
Session: P
Location: Exhibit Hall (Northeast, Southwest & Southeast)/Hilton
Date: Sunday, July 8th, 2007
Time: 8:00 AM
Number: P15022
Abstract ID:327


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