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Abstract Detail

Plant-Symbiont Interactions

Brazelton, Jessica N. [1], Coenen, Catharina [2], McSpadden Gardener, Brian B. [3].

2,4-Diacetylphloroglucinol, an Antibiotic Produced by Biocontrol Bacteria, Alters Plant Root Development.

Naturally occurring biocontrol strains of the soil bacterium Pseudomonas fluorescens can reduce the need for fungicides by excluding pathogens from the rhizosphere of crops and also stimulate root growth and crop yield. Root growth stimulation by some strains of P. fluorescens has been attributed to their ability to produce the plant hormone auxin, whereas biocontrol activity by some subspecies of P. fluorescens against pathogenic fungi depends in part on production of the antibiotic 2,4-diacetylphloroglucinol (DAPG). To understand effects of P. fluorescens biocontrol bacteria on plant root development, we used Salkowsky assays and a sensitive bioassay based on activation of the auxin-responsive GH3 promoter to characterize auxin production by twenty phlD+ strains of P. fluorescens isolated from native Ohio soils. None of the strains produced detectable auxin under our growth conditions; however, supernatants from all P. fluorescens strains tested inhibited GH3 promoter activity, suggesting that DAPG produced by these strains might inhibit auxin action. To investigate this possibility, we tested auxin-inducibility of the GH3::luciferase construct in tobacco hypocotyls in the presence of DAPG and also applied DAPG to tomato seedlings grown on agar media. DAPG concentrations that were inhibitory to tomato root growth also inhibited auxin-induction of GH3-promoter activity in tobacco hypocotyls, with inhibitory effects detectable as early as 8 minutes after auxin addition. By contrast, lower concentrations of DAPG increased the number and length of lateral roots in tomato seedlings incubated in the light. Although the molecular mechanisms of DAPG-action remain unresolved, our results suggest that DAPG may act as a regulator of plant root development.

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1 - Allegheny College, Biology, 520 N. Main st, Box #484, Meadville, PA, 16335, USA
2 - Allegheny College, Biology
3 - Ohio State University (OARDC), Plant Pathology

2,4-diacetylphloroglucinol (DAPG)
Pseudomonas fluorescens.

Presentation Type: Plant Biology Abstract
Session: P
Location: Exhibit Hall (Northeast, Southwest & Southeast)/Hilton
Date: Sunday, July 8th, 2007
Time: 8:00 AM
Number: P16013
Abstract ID:976

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