First published online March 7, 2002; 10.1104/pp.010805
Plant Physiol, April 2002, Vol. 128, pp. 1447-1454
A Small GTP-Binding Host Protein Is Required for Entry of
Powdery Mildew Fungus into Epidermal Cells of
Barley1
Holger
Schultheiss,
Cornelia
Dechert,
Karl-Heinz
Kogel, and
Ralph
Hückelhoven*
Institute of Phytopathology and Applied Zoology,
Justus-Liebig-University Giessen, Heinrich-Buff Ring 26-32,
D-35392 Giessen, Germany
Small GTP-binding proteins such as those from the RAC family
are cytosolic signal transduction proteins that often are involved in
processing of extracellular stimuli. Plant RAC proteins are implicated
in regulation of plant cell architecture, secondary wall formation,
meristem signaling, and defense against pathogens. We isolated a
RacB homolog from barley (Hordeum
vulgare) to study its role in resistance to the barley powdery
mildew fungus (Blumeria graminis f.sp.
hordei). RacB was constitutively
expressed in the barley epidermis and its expression level was not
strongly influenced by inoculation with B. graminis.
However, after biolistic bombardment of barley leaf segments with
RacB-double-stranded RNA, sequence-specific RNA
interference with RacB function inhibited fungal
haustorium establishment in a cell-autonomous and genotype-specific
manner. Mutants compromised in function of the Mlo
wild-type gene and the Ror1 gene (genotype mlo5
ror1) that are moderately susceptible to B.
graminis showed no alteration in powdery mildew resistance upon
RacB-specific RNA interference. Thus, the phenotype,
induced by RacB-specific RNA interference, was
apparently dependent on the same processes as
mlo5-mediated broad resistance, which is suppressed by
ror1. We conclude that an RAC small GTP-binding protein is
required for successful fungal haustorium establishment and that this
function may be linked to MLO-associated functions.
1
This work was supported by the Deutsche
Forschungsgemeinschaft (grant no. DFG Ko1208/8 to R.H. and
K.-H.K.).
*
Corresponding author; e-mail
Ralph.Hueckelhoven{at}agrar.uni-giessen.de; fax 49-641-9937499.
© 2002 American Society of Plant Physiologists
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