BMC Plant Biology
Volume 8
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Abstract (provisional)
Background
Tropospheric ozone, the most abundant air pollutant is detrimental to plant and animal health including humans. In sensitive plant species even a few hours of exposure to this potent oxidant leads to severe oxidative stress that manifests as visible cell death. In resistant plants usually no visible symptoms are observed. Naturally occurring variability to acute ozone in plants provides a valuable resource for examining molecular basis of the differences in responses to ozone. From our earlier study in Medicago truncatula, we have identified cultivar Jemalong is ozone sensitive and PI 464815 (JE154) is an ozone-resistant accession. Analyses of transcriptome changes in ozone-sensitive and resistant accession will provide important clues for understanding the molecular changes governing the plant responses to ozone.
Results
Acute ozone treatment (300 nL L-1 for six hours) led to a reactive oxygen species (ROS) burst in sensitive Jemalong six hours post-fumigation. In resistant JE154 increase in ROS levels was much reduced compared to Jemalong. Based on the results of ROS profiling, timepoints for microarray analysis were one hour into the ozone treatment, end of treatment and onset of an ozone-induced ROS burst at 12 hours. Replicated temporal transcriptome analysis in these two accessions were conducted using 17K oligonucleotide arrays. More than 2000 genes were differentially expressed in the two accessions. Significantly enriched gene ontologies (GOs) were identified using the Cluster Enrichment analysis software. Real-time PCR analysis was used to confirm the differential expression patterns of a subset of these genes.
Conclusions
This study provided a cogent view of the unique and shared transcriptional responses in an ozone-resistant and sensitive accession that exemplifies the complexity of oxidative signaling in plants. A striking finding was the alacrity of JE154 in altering its gene expression patterns in response to ozone, in stark contrast to delayed transcriptional response of Jemalong. GOs involved in signalling, hormonal pathways, antioxidants and secondary metabolism are altered in both accessions. However, the repertoire of genes responding in each of these categories was different between the two accessions. This study has identified unique genes and processes that will aid in dissecting the molecular mechanisms governing ozone resistance or sensitivity in plants.
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