WRKY transcription factors, oxidative protection and signalling in Salvia officinalis plants exposed to ozone

Tropospheric ozone (O3) is a global air pollutant that causes negative effects on plant life. The objective of this work is to give a characterization of the signalling pathway activated in response to O3 and to elucidate the potential role(s) of WRKY transcription factors in regulating oxidative protection and signalling in Salvia officinalis plants exposed to O3 (200 ppb, 5 h) in controlled environmental conditions. At the end of the treatment, leaves appeared symptomless. During the treatment and throughout the recovery period an alteration of membrane integrity was observed as confirmed by the marked increase of the content of thiobarbituric acid. An accumulation of hydrogen peroxide and a concomitant reduction of anion superoxide was detected, confirming that an oxidative burst had occurred. O3 triggered increases in phytohormones content already after 1 h of exposure. This seems to demonstrate that such signaling molecules (i.e. salycilic and jasmonic acids) could be considered a fast response to O3- perception. To identify WRKY transcriptional factors involved in the oxidative burst, BLASTX analysis against the current assembly of the S. miltiorrhiza sequence genome was performed using Arabidopsis WRKY protein sequences as queries. A total of six gene sequences were predicted for sage WRKYs. The relative gene expression analyses of WRKY were assessed by qRT-PCR. WRKYs were induced byO3 at different time-points. No significant expression level changes were observed during the recovery period. This suggests that WRKYs should be considered important players in the complex signalling processes during plant O3 responses.