Roles of Defense Hormones in the Regulation of Ozone-Induced Changes in Gene Expression and Cell Death

Abstract

Apoplast, the diffusional space between plant cell plasma membranes, is an important medium for signaling within and between the cells. Apoplastic reactive oxygen species (ROS) are crucial signaling molecules in various biological processes. ROS signaling is interconnected with the response to several hormones, including jasmonic acid (JA), salicylic acid (SA) and ethylene. Using ozone (O3) to activate apoplastic ROS signaling, we performed global and targeted analysis of transcriptional changes and cell death assays to dissect the contribution of hormone signaling and various transcription factors (TFs) in the regulation of gene expression and cell death. The contributions of SA, JA, and ethylene were assessed through analysis of single, double, and triple mutants deficient in biosynthesis or signaling for all three hormones. Even in the triple mutant, the global gene expression responses to O3 were mostly similar to the wild-type. Cell death in the JA receptor mutant coi1-16 was suppressed by impairment of the NADPH oxidase RBOHF, suggesting a role for a ROS signal in limiting the spread of cell death. In response to apoplastic ROS, there is not a single signaling pathway that regulates gene expression or cell death. Instead, several pathways regulate the apoplastic ROS response via combinatorial or overlapping mechanisms.

The ROS Wheel: Refining ROS Transcriptional Footprints

“…However, nearly all of these overlapping genes also were present in the 3-h cat2 study (102 DEGs), suggesting that elevated transcript levels of these genes are not restricted to early 1 O 2 signaling. Besides the cat2 and flu experiments, O 3 RNA-Seq studies (Xu et al, 2015a(Xu et al, , 2015b) also were highly consistent with our transcriptional footprints. For instance, induced genes of the ROS cluster V footprint Figure 7.…”

“…were more than 90% present in O 3 treatments performed in multiple Arabidopsis accessions (Xu et al, 2015a(Xu et al, , 2015b, as shown in Supplemental Figure S7. Hence, our footprints also can be implemented on data obtained from RNA-Seq and support the biological relevance of our meta-analysis results.…”

“…1 and FDR , 0.01) and 2,555 repressed genes (log 2 FC , 21 and FDR , 0.01; Supplemental Table S5). Such high numbers of DEGs also were retrieved after 2 h of flu reillumination (3,187 genes; Kim and Apel 2013) or 2 h of O 3 treatment in the wild-type background (5,168 genes; Xu et al, 2015a).…”

“…RBOHF activity is a crucial regulator of pathogen responses and associated metabolic adjustments (Chaouch et al, 2012). Furthermore, RBOHF was shown to enhance ROS production and cell death during ozone treatment, unlike RBOHD (Xu et al, 2015a). The transcriptional footprint of the RBOHF-containing cluster VII was limited to 126 induced genes.…”

“…Unlike the vast amounts of ATH1 microarray data that have documented oxidative stress responses at the transcript level, RNA-Seq studies are still outnumbered. Examples of oxidative stress RNA-Seq studies are a time-course experiment during reillumination of the flu mutant (Kim and Apel, 2013) and O 3 treatments in different accessions (Xu et al, 2015a(Xu et al, , 2015b. In order to assess transcriptional changes upon photorespiratory stress, we conducted an additional RNA-Seq study in cat2 mutants after 3 h of stress (Supplemental Materials and Methods S1).…”