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Appl. Environ. Microbiol., Jun 1997, 2287-2292, Vol 63, No. 6
V Hugouvieux, S Centis, C Lafitte and M Esquerre-Tugaye
The production of endopolygalacturonase (endoPG) by Colletotrichum
lindemuthianum, a fungal pathogen causing anthracnose on bean seedlings,
was enhanced when the fungus was grown in liquid medium with L-arabinose or
L-rhamnose as the sole carbon source. These two neutral sugars are present
in plant cell wall pectic polysaccharides. The endolytic nature of the
enzyme was demonstrated by its specific interaction with the
polygalacturonase-inhibiting protein of the host plant as well as by sugar
analysis of the products released from its action on oligogalacturonides.
Additional characterization of the protein was achieved with an antiserum
raised against the pure endoPG of the fungus. Induction by arabinose and
rhamnose was more prolonged and led to a level of enzyme activity at least
five times higher than that on pectin. Northern blot experiments showed
that this effect was correlated to the induction of a 1.6-kb transcript. A
dose-response study indicated that the endoPG transcript level was already
increased at a concentration of each sugar as low as 2.75 mM in the medium
and was maximum at 55 mM arabinose and 28 mM rhamnose. Glucose, the main
plant cell wall sugar residue which is also present in the apoplast,
prevented endoPG gene expression, partially when added to pectin at
concentrations ranging from 5 to 110 mM and totally when added at 55 mM to
arabinose. Inhibition by glucose of the rhamnose-induced endoPG was
correlated to nonuptake of rhamnose. This is the first report that
arabinose and rhamnose stimulate endoPG gene expression in a fungus. The
possible involvement of these various sugars on endoPG gene expression
during pathogenesis is discussed.
Copyright © 1997, American Society for Microbiology
Induction by (alpha)-L-Arabinose and (alpha)-L-Rhamnose of Endopolygalacturonase Gene Expression in Colletotrichum lindemuthianum
Centre de Biologie et Physiologie Vegetales, UMR CNRS-UPS 5546, Universite Paul Sabatier, 31062 Toulouse cedex, France
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