DIFFERENTIAL EXPRESSION OF CHITINASES IN VITIS-VINIFERA L RESPONDING TO SYSTEMIC ACQUIRED-RESISTANCE ACTIVATORS OR FUNGAL CHALLENGE

The concept of systemic acquired resistance (SAR) enables a novel appr oach to crop protection, and particular pathogenesis-related proteins, i.e. an acidic chitinase, have been classified as markers of the SAR response. Basic class I (VCHIT1b) and a class III (VCH3) chitinase cDN As were cloned from cultured Vitis vinifera L. cv Pinot Noir cells and used to probe the induction response of grapevine cells to salicylic acid or yeast elicitor. Furthermore, the cells were treated with the c ommercial SAR activators 2,6-dichloroiso-nicotinic acid or benzo(1,2,3 )-thiadiazole-7-carbothioic acid S-methyl ester. Elicitor or salicylic acid induced both VCHIT1b and VCH3 transcript abundances, whereas 2,6 -dichloroiso-nicotinic acid or benzo(1,2,3)thiadiazole-7-carbothioic a cid S-methyl ester enhanced exclusively the expression of VCH3. To ass ess the systemic sensation of chitinase expression, single leaves of V itis vinifera L. cv Pinot Noir or Vitis rupestris plants were inoculat ed with Plasmopara viticola spore suspensions, and the VCH3 and VCHIT1 b mRNA amounts in the infected versus the adjacent, healthy leaf were monitored. Two VCH3 mRNA maxima were observed 2 and 6 d postinoculatio n in the infected, susceptible V. vinifera tissue, whereas in the heal thy leaf the transcript increased from low levels d 2 postinoculation to prominent levels d 6 to 8 postinoculation. The level of VCH3 mRNA i ncreased also over 4 d in the inoculated, resistant V. rupestris tissu e. However, necrotic spots rapidly limited the infection, and the VCH3 transcript was undetectable in the upper-stage, healthy leaf. The exp ression of VCHIT1b remained negligible under either experimental condi tion. Overall, the results suggest that the selective expression of VC H3 might be a reliable indicator of the SAR response in V. vinifera L.