Project description:Arabidopsis thaliana cell suspension cultures (ACSC) were subjected to 30-min, mild chemical treatments with three different singlet oxygen elicitors at low-medium light conditions (150 µE m–2 s–1) with the aim of getting a better understanding of singlet oxygen-mediated defence responses in plants. The three elicitors Indigo Carmine (IC), Methylene Violet (MV) and Rose Bengal (RB) at a concentration of 0.5 µM were chosen because they exhibited different abilities to permeate the plasma membrane and to accumulate in the cell soma or organelles such as chloroplasts. In addition, ACSC were treated with 500 µM H2O2 for comparison. Confocal image analysis of Arabidopsis cells revealed that IC was not retained in cells, whereas MV and RB permeated the plasma membrane and accumulated in the chloroplast envelope and inside chloroplasts, respectively. As a consequence of their different cellular location, the physiological, transcriptional and photosynthetic responses of Arabidopsis cells to singlet oxygen production varied from each other and the activation of programmed cell death (PCD) was observed in ACSC treated with 0.5 µM RB, but not with the other elicitor nor with 500 µM H2O2. The role of chloroplasts in the activation of PCD was further investigated when this physiological response was analyzed in dark-grown cell cultures containing undifferentiated plastids. Interestingly, PCD was only activated in light-grown, but not in dark-grown, Arabidopsis cell cultures, suggesting that singlet oxygen-mediated defence responses were initiated inside chloroplasts. Genome-wide transcriptional profile analyses were performed as well and the results proved that there were only statistically significant changes in the transcript expression of light-grown ACSC treated with 0.5 µM RB and 500 µM H2O2, but not with IC nor with MV. Functional enrichment analyses revealed that GO/Biological process terms associated with defence responses were common in the treatments with 0.5 µM RB and 500 µM H2O2; however, resistance response to pathogen and PCD terms were only significantly over-represented in the RB treatment. Moreover, the analysis of the up-regulated transcripts in ACSC treated with 0.5 µM RB brought out that both specific markers for singlet oxygen from the conditional fluorescence (flu) mutant of Arabidopsis and transcripts with a key role in hormone-activated PCD (i.e. ethylene and jasmonic acid) were present, although there was no evidence for the up-regulation of EDS1 encoding the ENHANCED DISEASE SUSCEPTIBILITY PROTEIN 1. Finally, a co-regulation analysis proved that ACSC treated with 0.5 µM RB exhibited higher correlation with the flu family mutants than with other singlet oxygen producer mutants of Arabidopsis or wild-type plants of Arabidopsis subjected to high light treatments, where singlet oxygen was produced in photosystem II and an acclimatory response was activated instead of PCD.

Project description:Arabidopsis thaliana cell suspension cultures (ACSC) were subjected to 30-min, mild chemical treatments with three different singlet oxygen elicitors at low-medium light conditions (150 µE m–2 s–1) with the aim of getting a better understanding of singlet oxygen-mediated defence responses in plants. The three elicitors Indigo Carmine (IC), Methylene Violet (MV) and Rose Bengal (RB) at a concentration of 0.5 µM were chosen because they exhibited different abilities to permeate the plasma membrane and to accumulate in the cell soma or organelles such as chloroplasts. In addition, ACSC were treated with 500 µM H2O2 for comparison. Confocal image analysis of Arabidopsis cells revealed that IC was not retained in cells, whereas MV and RB permeated the plasma membrane and accumulated in the chloroplast envelope and inside chloroplasts, respectively. As a consequence of their different cellular location, the physiological, transcriptional and photosynthetic responses of Arabidopsis cells to singlet oxygen production varied from each other and the activation of programmed cell death (PCD) was observed in ACSC treated with 0.5 µM RB, but not with the other elicitor nor with 500 µM H2O2. The role of chloroplasts in the activation of PCD was further investigated when this physiological response was analyzed in dark-grown cell cultures containing undifferentiated plastids. Interestingly, PCD was only activated in light-grown, but not in dark-grown, Arabidopsis cell cultures, suggesting that singlet oxygen-mediated defence responses were initiated inside chloroplasts. Genome-wide transcriptional profile analyses were performed as well and the results proved that there were only statistically significant changes in the transcript expression of light-grown ACSC treated with 0.5 µM RB and 500 µM H2O2, but not with IC nor with MV. Functional enrichment analyses revealed that GO/Biological process terms associated with defence responses were common in the treatments with 0.5 µM RB and 500 µM H2O2; however, resistance response to pathogen and PCD terms were only significantly over-represented in the RB treatment. Moreover, the analysis of the up-regulated transcripts in ACSC treated with 0.5 µM RB brought out that both specific markers for singlet oxygen from the conditional fluorescence (flu) mutant of Arabidopsis and transcripts with a key role in hormone-activated PCD (i.e. ethylene and jasmonic acid) were present, although there was no evidence for the up-regulation of EDS1 encoding the ENHANCED DISEASE SUSCEPTIBILITY PROTEIN 1. Finally, a co-regulation analysis proved that ACSC treated with 0.5 µM RB exhibited higher correlation with the flu family mutants than with other singlet oxygen producer mutants of Arabidopsis or wild-type plants of Arabidopsis subjected to high light treatments, where singlet oxygen was produced in photosystem II and an acclimatory response was activated instead of PCD. 18 Samples total. Six Samples are controls, 3 Samples each treated with Rose Bengal, Hydrogen Peroxide, Methyl Violet, and Indigo Carmine.

Project description:The yellow variegated2 (var2) mutant in Arabidopsis thaliana has been studied as a typical leaf-variegated mutant whose defect results from the lack of FtsH2 metalloprotease in chloroplasts. The var2 green sectors suffer from photooxidative stress and accumulate high levels of reactive oxygen species (ROS) because of compromised Photosystem II repair. This study investigated and compared microarray-based expression profiles of green and white sectors of var2 leaves. Results suggest that ROS that accumulate in chloroplasts of var2 green sectors do not cause much significant change of the transcriptional profile related to ROS signaling and scavenging. In contrast, transcriptome in white sectors apparently differs from those in green sectors and wild type. Numerous genes related to photosynthesis and chloroplast functions were repressed in white sectors. Furthermore, many genes related to oxidative stress were up-regulated. Among them, we specifically examined ROS scavenging genes, such as Cu/Zn superoxide dismutase 2 (CSD2), that were apparently up-regulated in white but not in green sectors. Up-regulation of CSD2 appears to be partly attributable to the lack of a microRNA (miR398) in white sectors. Together, we concluded that white sectors exhibit response to oxidative and other stresses, including CSD2 up-regulation, which might be commonly found in tissues with abnormal chloroplast differentiation. Arabidopsis thaliana ecotype Columbia (Col), used as the wild-type, and var2-1 (var2) were grown in MS medium supplemented with Gamborgâ??s vitamins (Sigma-Aldrich). MS medium was supplemented with 1.5% (w/v) sucrose and 0.7% (w/v) agar. Plants were maintained under a 12 h light (70 Î¼molâ?¢m-2â?¢s-1)/12 h dark cycle at 22Â°C. Green and white sectors, surgically separated and collected from 4-week-old true leaves were subjected to total RNA extraction. We also extracted total RNA from Col. Three biological replicates were performed for each sample.

Dataset Information

Gene expression from Arabidopsis under high light conditions

Publications

Early transcriptional defense responses in Arabidopsis cell suspension culture under high-light conditions.

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