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Transcriptome in Arabidopsis yellow variegated 2 (var2)

ABSTRACT: 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.

ORGANISM(S): Arabidopsis thaliana

PROVIDER: GSE18646 | GEO | 2010/03/31

SECONDARY ACCESSION(S): PRJNA121581

REPOSITORIES: GEO

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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.

Project description:Regulation of expression of genes encoding chloroplast components is critical to the autotrophic plant and never more so than in the cotyledons of the de-etiolating seedling. Many chloroplast proteins are nuclear-encoded and a retrograde signal from the chloroplasts (the Plastid Signal) modulates nuclear transcription. However, not all chloroplast-targeted genes are subject to this control and not all plastid-dependent nuclear genes are chloroplast-targeted. We therefore aim to provide the most comprehensive screen yet of which genes are affected by plastid-signalling. To specifically knock-out positive plastid signalling in light-grown cotyledons, the herbicide Norflurazon (NF) is supplied in the growth medium, causing a carotenoid deficiency that leaves the chloroplasts vulnerable to photobleaching. This blocks the expression of a subset of nuclear genes, such as Lhcb and HEMA1. Two pairs of RNAs will directly compare the transcription in seedlings grown under continuous white light with and without NF. A third RNA will also be compared from a mutant that shows a degree of constitutive positive plastid signalling. These two mutants act synergistically to counteract the effect of NF on nuclear transcription. The gun1,gun5 double mutant maintains a significantly higher level of Lhcb and HEMA1 expression in the presence of photobeached chloroplasts than the NF-treated wild-type. This transcriptome set will therefore complement RNA1 (wild-type+NF) and indicate which of the genes identified from the RNA1/RNA2 comparison are subject to the particular gun1/gun5 plastid signalling pathway(s). The growth of conditions of the seedlings (namely on MS medium supplemented with 1.5% sucrose, for 3 days under continuous WL following 2 days germination in darkness) has been chosen from the results of our own recent studies using Northern blotting techniques that show these conditions to maximise the respective NF and gun mutant effects on Lhcb and HEMA1 gene expression. This experiment is part one of a two-part study to compare the transcriptional output of this NF-affected pathway with that of a newly discovered FR-mediated pathway. A subsequent array experiment will assess the nuclear response as affected by this FR/ phyA-input pathway and the two sets of array data will be compared and contrasted. Note: Col-0 wild-type (NASC code N1092). gun1,gun5 double mutant(obtained from Enriquez Lopez-Juez, Royal Holloway, University of London.(Mochizuki et al. 2001 PNAS 98: 2053-2058). This line cannot be donated by us as it is the IP of Joanne Chory (SALK Institute, USA). Treatment = a herbicide (Norflurazon) application which leads to chloroplast photobleaching and hence down regulation of nuclear genes dependent on plastid signalling from intact chloroplasts.

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Transcriptome in Arabidopsis yellow variegated 2 (var2)

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