Ozone Induced Transcriptome in Two Differentially Susceptible Poplar Genotypes

As consequence of both industrialization and other anthropogenic activities, the basal concentrations of tropospheric ozone significantly increased during the last years, with harmfull consequences on physiological and biochemical processes of trees. Also the intensities and the frequencies of the episodic O3-peaks considerably increased. In order to investigate the molecular responses of deciduous long living trees to episodic peaks of ozone, as frequently may occur in the most urbanized areas of the world, we exposed to a single O3 pulse of 150 ppb for 5 hours, two poplar clones differentially susceptible in terms of leaf injuries (the O3-sensitive Populus deltoides x maximowiczii, Eridano clone, and the O3-tolerant Populus x euroamericana, I-214 clone). Unfumigated plants were used as controls. The transcriptional responses evoked by ozone stress in the leaves from both the poplar clones were investigated by using a microarray constituted by a collection of cDNAs isolated from the leaves of I-214 and Eridano polar clones subjected to an acute ozone stress and also from Populus alba and Platanus acerifolia leaves respectively exposed to cold stress and to exogenous cerato-platanin phytotoxic protein. Gene expression profiles at the O3 fumigation end were compared with those of control plants in both the clones. Out of the 337 genes, 119 and 41 genes were evidenced O3-responsive in Eridano and in I-214 poplar clones respectively. In both the genotypes (especially in the Eridano clone), the down-regulated genes were higher in number than the up-regulated ones. Almost all the O3-deregulated genes resulted differentially regulated also in the sensitive poplar clone. However, sensitive and resistant genotypes evidenced also some genes specifically up or down expressed only in one of the two clones. These genes could play a key role in determining the different behaviour displayed by the two clones when exposed to acute ozone stress and constitute an intriguing opportunity to better understand the molecular bases of ozone stress tolerance and sensitivity. The transcription profiles, obtained by using these cDNA microarray platforms, indicated that several genes differentially regulated by ozone in Eridano and I-214 poplar clones were the same regulated by cold and cerato-platanin in Populus alba and Platanus acerifolia trees, underlying the existence of a conserved and interspecific network of genes, activated by different stresses during plant defence responses