Plants exhibit a robust transcriptional response to gamma radiation which includes the induction of transcripts required for homologous recombination and the suppression of transcripts that promote cell cycle progression. Various DNA damaging agents induce different spectra of DNA damage as well as collateral damage to other cellular components and therefore are not expected to provoke identical responses by the cell. Here we study the effects of two different types of ionizing radiation (IR) treatment HZE (1 GeV Fe26+ high mass high charge and high energy relativistic particles) and gamma photons on the transcriptome of Arabidopsis thaliana seedlings. Both types of IR induce small clusters of radicals that can result in the formation of double strand breaks (DSBs) but HZE also produces linear arrays of extremely clustered damage. We performed these experiments across a range of time points (1.5-24 h after irradiation) in both wild-type plants and in mutants defective in the DSB-sensing protein kinase ATM. The two types of IR exhibit a shared double strand break-repair-related damage response although they differ slightly in the timing degree and ATM-dependence of the response. The ATM-dependent DNA metabolism-related transcripts of the xd2DSB response xd3 were also induced by other DNA damaging agents but were not induced by conventional stresses. Both Gamma and HZE irradiation induced at 24 h post-irradiation ATM-dependent transcripts associated with a variety of conventional stresses; these were overrepresented for pathogen response rather than DNA metabolism. In contrast only HZE-irradiated plants at 1.5 h after irradiation exhibited an additional and very extensive transcriptional response shared with plants experiencing extended night. This response was not apparent in gamma-irradiated plants. We treated 5-day-old WT and atm-1 seedlings of Arabidopsis thaliana with 100 Gy of Gamma radiation (over a span of 15 minutes) or 30 Gy of HZE (over a span of approximately 12 minutes). Gamma irradiations were completed at 8:40 am while HZE irradiations were conducted in two runs (due to space limitations) which were completed at 1:09 and 1:28pm respectively. Gamma treated seedlings were sampled at 10:10 am 11:40 am 2:55 pm 8:40 pm and 8:40 am. HZE treated seedlings were sampled at 2:39 pm 4:09 pm 7:24 pm 1:09 am and 1:09 pm. Un-irradiated WT and atm-1 control seedlings were sampled at 10:45 am on Day #1 and 9:15 am on Day #2. There are a total of 22 experimental or control conditions with two replicates per condition yielding 44 samples overall.

Plants exhibit a robust transcriptional response to gamma radiation which includes the induction of transcripts required for homologous recombination and the suppression of transcripts that promote cell cycle progression. Various DNA damaging agents induce different spectra of DNA damage as well as collateral damage to other cellular components and therefore are not expected to provoke identical responses by the cell. Here we study the effects of two different types of ionizing radiation (IR) treatment HZE (1 GeV Fe26+ high mass high charge and high energy relativistic particles) and gamma photons on the transcriptome of Arabidopsis thaliana seedlings. Both types of IR induce small clusters of radicals that can result in the formation of double strand breaks (DSBs) but HZE also produces linear arrays of extremely clustered damage. We performed these experiments across a range of time points (1.5-24 h after irradiation) in both wild-type plants and in mutants defective in the DSB-sensing protein kinase ATM. The two types of IR exhibit a shared double strand break-repair-related damage response although they differ slightly in the timing degree and ATM-dependence of the response. The ATM-dependent DNA metabolism-related transcripts of the DSB response were also induced by other DNA damaging agents but were not induced by conventional stresses. Both Gamma and HZE irradiation induced at 24 h post-irradiation ATM-dependent transcripts associated with a variety of conventional stresses; these were overrepresented for pathogen response rather than DNA metabolism. In contrast only HZE-irradiated plants at 1.5 h after irradiation exhibited an additional and very extensive transcriptional response shared with plants experiencing extended night. This response was not apparent in gamma-irradiated plants.

Plants exhibit a robust transcriptional response to gamma radiation which includes the induction of transcripts required for homologous recombination and the suppression of transcripts that promote cell cycle progression. Various DNA damaging agents induce different spectra of DNA damage as well as collateral damage to other cellular components and therefore are not expected to provoke identical responses by the cell. Here we study the effects of two different types of ionizing radiation (IR) treatment, HZE (1 GeV Fe26+ high mass, high charge, and high energy relativistic particles) and gamma photons, on the transcriptome of Arabidopsis thaliana seedlings. Both types of IR induce small clusters of radicals that can result in the formation of double strand breaks (DSBs), but HZE also produces linear arrays of extremely clustered damage. We performed these experiments across a range of time points (1.5-24 h after irradiation) in both wild-type plants and in mutants defective in the DSB-sensing protein kinase ATM. The two types of IR exhibit a shared double strand break-repair-related damage response, although they differ slightly in the timing, degree, and ATM-dependence of the response. The ATM-dependent, DNA metabolism-related transcripts of the DSB response were also induced by other DNA damaging agents, but were not induced by conventional stresses. Both Gamma and HZE irradiation induced, at 24 h post-irradiation, ATM-dependent transcripts associated with a variety of conventional stresses; these were overrepresented for pathogen response, rather than DNA metabolism. In contrast, only HZE-irradiated plants, at 1.5 h after irradiation, exhibited an additional and very extensive transcriptional response, shared with plants experiencing extended night. This response was not apparent in gamma-irradiated plants. We treated 5-day-old WT and atm-1 seedlings of Arabidopsis thaliana with 100 Gy of Gamma radiation (over a span of 15 minutes) or 30 Gy of HZE (over a span of approximately 12 minutes). Gamma irradiations were completed at 8:40 am, while HZE irradiations were conducted in two runs (due to space limitations) which were completed at 1:09 and 1:28pm respectively. Gamma treated seedlings were sampled at 10:10 am, 11:40 am, 2:55 pm, 8:40 pm, and 8:40 am. HZE treated seedlings were sampled at 2:39 pm, 4:09 pm, 7:24 pm, 1:09 am, and 1:09 pm. Un-irradiated WT and atm-1 control seedlings were sampled at 10:45 am on Day #1 and 9:15 am on Day #2. There are a total of 22 experimental or control conditions, with two replicates per condition, yielding 44 samples overall.

Gene expression profile of two-week-old etiolated Arabidopsis seedlings under microgravity on board space flight BRIC16 were compared with ground grown control in both wild-type and act2-3 mutant plants.

Whole seedlings of wild type (4d) and atm mutants (4d) have been analyzed after a gamma ray irradiation of 0.75h 1.5h 3h & 5h (time course). Roots of wt (4d) atm (3d) and atr (4d) mutants have been analyzed after a 1h irradiation. Ataxia Telangiectasia Mutated (ATM) encodes a large protein with a phosphatidylinositol 3-kinase (PI3K)-like domain at the C terminus (reviewed by Rotman and Shiloh 1998). PI3K-related proteins make up a large family of Ser-Thr protein kinases numerous members of which are involved in the regulation of cell cycle progression responses to DNA damage and the maintenance of genomic stability (Hoekstra 1997). AtATM plays an essential role in meiosis and in the somatic response to DNA damage in plants similar to the function of ATM in mammals and other eukaryotes. Ataxia telangiectasia-mutated and Rad3-related (ATR) plays a central role in cell-cycle regulation transmitting DNA damage signals to downstream effectors of cell-cycle progression.

Gene expression profile of two-week-old etiolated Arabidopsis seedlings under microgravity on board space flight BRIC16 were compared with ground grown control in both wild-type and act2-3 mutant plants.

We address a key baseline question of whether gene expression changes are induced by the orbital environment and then we ask whether undifferentiated cells cells presumably lacking the typical gravity response mechanisms perceive spaceflight. Arabidopsis seedlings and undifferentiated cultured Arabidopsis cells were launched in April 2010 as part of the BRIC-16 flight experiment on STS-131. Biologically replicated DNA microarray and averaged RNA digital transcript profiling revealed several hundred genes in seedlings and cell cultures that were significantly affected by launch and spaceflight. The response was moderate in seedlings; only a few genes were induced by more than 7-fold and the overall intrinsic expression level for most differentially expressed genes was low. In contrast cell cultures displayed a more dramatic response with dozens of genes showing this level of differential expression a list comprised primarily of heat shock-related and stress-related genes. This baseline transcriptome profiling of seedlings and cultured cells confirms the fundamental hypothesis that survival of the spaceflight environment requires adaptive changes that are both governed and displayed by alterations in gene expression. The comparison of intact plants with cultures of undifferentiated cells confirms a second hypothesis: undifferentiated cells can detect spaceflight in the absence of specialized tissue or organized developmental structures known to detect gravity.

We address a key baseline question of whether gene expression changes are induced by the orbital environment and then we ask whether undifferentiated cells cells presumably lacking the typical gravity response mechanisms perceive spaceflight. Arabidopsis seedlings and undifferentiated cultured Arabidopsis cells were launched in April 2010 as part of the BRIC-16 flight experiment on STS-131. Biologically replicated DNA microarray and averaged RNA digital transcript profiling revealed several hundred genes in seedlings and cell cultures that were significantly affected by launch and spaceflight. The response was moderate in seedlings; only a few genes were induced by more than 7-fold and the overall intrinsic expression level for most differentially expressed genes was low. In contrast cell cultures displayed a more dramatic response with dozens of genes showing this level of differential expression a list comprised primarily of heat shock-related and stress-related genes. This baseline transcriptome profiling of seedlings and cultured cells confirms the fundamental hypothesis that survival of the spaceflight environment requires adaptive changes that are both governed and displayed by alterations in gene expression. The comparison of intact plants with cultures of undifferentiated cells confirms a second hypothesis: undifferentiated cells can detect spaceflight in the absence of specialized tissue or organized developmental structures known to detect gravity.

Martian regolith (unconsolidated surface material) is a potential medium for plant growth in bioregenerative life support systems during manned missions on Mars. However hydrated magnesium sulfate mineral levels in the regolith of Mars can reach as high as 10 wt% and would be expected to be highly inhibitory to plant growth. A global approach was used to identify novel genes with potential to enhance tolerance to high MgSO4 stress. The early Arabidopsis root transcriptome response to elevated concentrations of magnesium sulfate was characterized in col-0 and also between col-0 and the mutant line cax1-1 - a mutant relatively tolerant of high levels of MgSO4-7H2O in soil solution. After 3 weeks of growth under hydroponic conditions Arabidopsis thaliana col-0 roots were exposed to a basic nutrient solution (0.25 g/L MES 1/16x MS pH 5.7) with an additional 2.08 mM magnesium sulfate (total Ca:Mg ratio = 1:15) for 45 min. 90 min. or 180 min. while a col-0 control set was exposed to the basic nutrient solution without additional magnesium sulfate for 45 minutes. Arabidopsis thaliana cax1-1 roots were exposed to the basic nutrient solution with additional magnesium sulfate for 180 min. only. Four replicate containers were harvested for the control and each of the treatment sets resulting in a total of 20 samples. Gene expression of the col-0 sets exposed to magnesium sulfate treatment for 45 min. 90 min. or 180 min. was compared to gene expression of the col-0 control set. Gene expression of the cax1-1 set exposed to magnesium sulfate treatment for 180 min. was compared to gene expression of the col-0 set exposed to magnesium sulfate treatment for 180 minutes.

Martian regolith (unconsolidated surface material) is a potential medium for plant growth in bioregenerative life support systems during manned missions on Mars. However hydrated magnesium sulfate mineral levels in the regolith of Mars can reach as high as 10 wt% and would be expected to be highly inhibitory to plant growth. A global approach was used to identify novel genes with potential to enhance tolerance to high MgSO4 stress. The early Arabidopsis root transcriptome response to elevated concentrations of magnesium sulfate was characterized in col-0 and also between col-0 and the mutant line cax1-1 - a mutant relatively tolerant of high levels of MgSO4-7H2O in soil solution. After 3 weeks of growth under hydroponic conditions Arabidopsis thaliana col-0 roots were exposed to a basic nutrient solution (0.25 g/L MES 1/16x MS pH 5.7) with an additional 2.08 mM magnesium sulfate (total Ca:Mg ratio = 1:15) for 45 min. 90 min. or 180 min. while a col-0 control set was exposed to the basic nutrient solution without additional magnesium sulfate for 45 minutes. Arabidopsis thaliana cax1-1 roots were exposed to the basic nutrient solution with additional magnesium sulfate for 180 min. only. Four replicate containers were harvested for the control and each of the treatment sets resulting in a total of 20 samples. Gene expression of the col-0 sets exposed to magnesium sulfate treatment for 45 min. 90 min. or 180 min. was compared to gene expression of the col-0 control set. Gene expression of the cax1-1 set exposed to magnesium sulfate treatment for 180 min. was compared to gene expression of the col-0 set exposed to magnesium sulfate treatment for 180 minutes.