PLANT PHYSIOLOGY , Vol 115, Issue 4 1557-1567, Copyright © 1997 by American Society of Plant Biologists
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PLANT-MICROBE AND PLANT-INSECT INTERACTIONS |
RNase Activity Prevents the Growth of a Fungal Pathogen in Tobacco Leaves and Increases upon Induction of Systemic Acquired Resistance with Elicitin
E. Galiana, P. Bonnet, S. Conrod, H. Keller, F. Panabieres, M. Ponchet, A. Poupet and P. Ricci
Station de Botanique et de Pathologie Vegetale, Institute National de la Recherche Agronomique, Villa Thuret, BP 2078, F-06606, Antibes cedex, France
The hypersensitive response and systemic acquired resistance (SAR) can be
induced in tobacco (Nicotiana tabacum L.) plants by cryptogein, an elicitin
secreted by Phytophthora cryptogea. Stem application of cryptogein leads to
the establishment of acquired resistance to subsequent leaf infection with
Phytophthora parasitica var nicotianae, the agent of the tobacco black
shank disease. We have studied early events that occur after the infection
and show here that a tobacco gene encoding the extracellular S-like RNase
NE is expressed in response to inoculation with the pathogenic fungus. Upon
induction of SAR with cryptogein, the accumulation of NE transcripts
coincided with a rapid induction of RNase activity and with the increase in
the activity of at least two different extracellular RNases. Moreover,
exogenous application of RNase activity in the extracellular space of
leaves led to a reduction of the fungus development by up to 90%,
independently of any cryptogein treatment and in the absence of apparent
necrosis. These results indicate that the up-regulation of apoplastic RNase
activity after inoculation could contribute to the control of fungal
invasion in plants induced to SAR with cryptogein.
