6533b831fe1ef96bd129842f

RESEARCH PRODUCT

Preferential induction of 20S proteasome subunits during elicitation of plant defense reactions: towards the characterization of "plant defense proteasomes".

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Plants have evolved efficient mechanisms to resist pathogens. The earliest defense response is the hypersensitive response (HR) considered as the main step leading to plant systemic acquired resistance (SAR) that protects the whole plant against a large spectrum of pathogens. We showed previously that elicitation of defense reactions in tobacco cells by cryptogein, a proteinaceous elicitor of plant defense reactions, leads to a rapid and differential accumulation of transcripts corresponding to genes encoding defense-induced (din) subunits of 20S proteasome: beta1din, alpha3din and alpha6din.Here, expression of these three subunits was investigated by Northern blotting and by Western blotting using specific antibodies synthesized against two peptides deduced from the beta1din, alpha3din or alpha6din encoding sequence. Kinetics of mRNA and protein accumulation in various defense models showed a simultaneous accumulation of beta1din, alpha3din and alpha6din corresponding mRNAs and proteins only in plants developing a systemic acquired resistance. Inhibition by diphenyleneiodonium of the oxidative burst induced in defense reactions blocked the expression of beta1din, alpha3din and alpha6din. Using 2D gel electrophoresis and Western blotting, we showed multiple spots for each induced subunit suggesting the possible existence of multigenic families confirmed by genomic DNA analysis. These results suggest a complex regulation of induced subunits tightly correlated with the activation of plant defense reactions. beta1din, alpha3din and alpha6din subunits could probably replace the corresponding constitutive subunits in 20S proteasome leading to "plant defense proteasomes" which could play an important role in plant defense reactions.