Effect of Light and Dark on the Phenolic Compound Accumulation in Tartary Buckwheat Hairy Roots Overexpressing ZmLC.

Fagopyrum tataricum 'Hokkai T10' is a buckwheat cultivar capable of producing large amounts of phenolic compounds, including flavonoids (anthocyanins), phenolic acids, and catechin, which have antioxidant, anticancer, and anti-inflammatory properties. In the present study, we revealed that the maize transcription factor Lc increased the accumulation of phenolic compounds, including sinapic acid, 4-hydroxybenzonate, t-cinnamic acid, and rutin, in Hokkai T10 hairy roots cultured under long-photoperiod (16 h light and 8 h dark) conditions. The transcription factor upregulated phenylpropanoid and flavonoid biosynthesis pathway genes, yielding total phenolic contents reaching 27.0 ± 3.30 mg g-1 dry weight, 163% greater than the total flavonoid content produced by a GUS-overexpressing line (control). In contrast, when cultured under continuous darkness, the phenolic accumulation was not significantly different between the ZmLC-overexpressing hairy roots and the control. These findings suggest that the transcription factor (ZmLC) activity may be light-responsive in the ZmLC-overexpressing hairy roots of F. tataricum, triggering activation of the phenylpropanoid and flavonoid biosynthesis pathways. Further studies are required on the optimization of light intensity in ZmLC-overexpressing hairy roots of F. tataricum to enhance the production of phenolic compounds.

Novel Transcriptome Study and Detection of Metabolic Variations in UV-B-Treated Date Palm (Phoenix dactylifera cv. Khalas).

Date palm (Phoenix dactylifera) is one of the most widespread fruit crop species and can tolerate drastic environmental conditions that may not be suitable for other fruit species. Excess UV-B stress is one of the greatest concerns for date palm trees and can cause genotoxic effects. Date palm responds to UV-B irradiation through increased DEG expression levels and elaborates upon regulatory metabolic mechanisms that assist the plants in adjusting to this exertion. Sixty-day-old Khalas date palm seedlings (first true-leaf stage) were treated with UV-B (wavelength, 253.7 nm; intensity, 75 µW cm-2 for 72 h (16 h of UV light and 8 h of darkness). Transcriptome analysis revealed 10,249 and 12,426 genes whose expressions were upregulated and downregulated, respectively, compared to the genes in the control. Furthermore, the differentially expressed genes included transcription factor-encoding genes and chloroplast- and photosystem-related genes. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) was used to detect metabolite variations. Fifty metabolites, including amino acids and flavonoids, showed changes in levels after UV-B excess. Amino acid metabolism was changed by UV-B irradiation, and some amino acids interacted with precursors of different pathways that were used to synthesize secondary metabolites, i.e., flavonoids and phenylpropanoids. The metabolite content response to UV-B irradiation according to hierarchical clustering analysis showed changes in amino acids and flavonoids compared with those of the control. Amino acids might increase the function of scavengers of reactive oxygen species by synthesizing flavonoids that increase in response to UV-B treatment. This study enriches the annotated date palm unigene sequences and enhances the understanding of the mechanisms underlying UV-B stress through genetic manipulation. Moreover, this study provides a sequence resource for genetic, genomic and metabolic studies of date palm.

Comparative transcriptome analysis of Haematococcus pluvialis on astaxanthin biosynthesis in response to irradiation with red or blue LED wavelength.

The unicellular green microalga Haematococcus pluvialis has the highest content of the natural antioxidant, astaxanthin. Previously, it was determined that astaxanthin accumulation in H. pluvialis could be induced by blue-wavelength irradiation; however, the molecular mechanism remains unknown. The present study aimed to compare the transcriptome of H. pluvialis, with respect to astaxanthin biosynthesis, under the monochromatic red (660 nm) or blue (450 nm) light-emitting diode (LED) irradiation. Among a total of 165,372 transcripts, we identified 67,703 unigenes, of which 2245 and 171 were identified as differentially expressed genes (DEGs) in response to blue and red irradiation, respectively. Interestingly, expressional changes of blue light receptor cryptochromes were detected in response to blue and/or red LED irradiation in H. pluvialis, which may directly and indirectly regulate astaxanthin biosynthesis. In accordance with this observation, expression of the BKT and CHY genes, which are part of the downstream section of the astaxanthin biosynthetic pathway, was significantly upregulated by blue LED irradiation compared with their expression under control white irradiation. Contrastingly, they were downregulated by red LED irradiation. Our transcriptome study provided molecular insights that highlighted the different of responses of H. pluvialis to red and blue irradiation, especially for astaxanthin biosynthesis.

Arabidopsis thaliana thymidine kinase 1a is ubiquitously expressed during development and contributes to confer tolerance to genotoxic stress.

Thymidine kinase catalyzes the first step in the nucleotide salvage pathway by transferring a phosphate group to a thymidine molecule. In mammals thymidine kinase supplies deoxyribonucleotides for DNA replication and DNA repair, and the expression of the gene is tightly regulated during the cell cycle. Although this gene is phylogenetically conserved in many taxa, its physiological function in plants remains unknown. The genome of the model plant Arabidopsis thaliana has two thymidine kinase genes (AtTK1a and AtTK1b) and microarray data suggest they might have redundant roles. In this study we analyzed the TK1a function by evaluating its expression pattern during development and in response to genotoxic stress. We also studied its role in DNA repair by the characterization of a mutant that contained the T-DNA insertion in the promoter region of the TK1a gene. We found that TK1a is expressed in most tissues during plant development and it was differentially induced by ultraviolet-C radiation because TK1b expression was unaffected. In the mutant, the T-DNA insertion caused a 40 % rise in transcript levels and enzyme activity in Arabidopsis seedlings compared to wild-type plants. This elevation was enough to confer tolerance to ultraviolet-C irradiation in dark conditions, as determined by root growth, and meristem length and structure. TK1a overexpression also provided tolerance to genotoxins that induce double-strand break. Our results suggest that thymidine kinase contributes to several DNA repair pathways by providing deoxythymidine triphosphate that serve as precursors for DNA repair and to balance deoxyribonucleotides pools.

Expression of the high light-inducible Dunaliella LIP promoter in Chlamydomonas reinhardtii.

The development of highly inducible promoters is critical for designing effective transformation systems for transgenic analyses. In this study, we investigated the promoter of the light-inducible protein gene (LIP) of the marine alga Dunaliella sp. LIPs are homologs of the early light-induced proteins (ELIPs) of Arabidopsis thaliana. DNA sequence analysis revealed that the LIP promoter contains several light-responsive motifs. Constructs containing progressive truncations of the LIP promoter fused with a Renilla luciferase gene were introduced into Chlamydomonas reinhardtii to identify the light-responsive region in the promoter. Transcription from the LIP promoter was stimulated by high light (HL) in a light intensity-dependent manner. In contrast, oxidative stress induced by chemicals had little effect on the LIP promoter, which implies that the LIP promoter is exclusively induced by high light. Truncation of the promoter to a -100 base pair (bp) region abrogated light inducibility, which suggests the presence of a negative cis-regulatory element upstream of the -100 bp fragment. The LIP promoter can be utilized in transgenic research to specifically select and propagate transgenic microalgae under high-light conditions.

Canopy light cues affect emission of constitutive and methyl jasmonate-induced volatile organic compounds in Arabidopsis thaliana.

The effects of plant competition for light on the emission of plant volatile organic compounds (VOCs) were studied by investigating how different light qualities that occur in dense vegetation affect the emission of constitutive and methyl-jasmonate-induced VOCs. Arabidopsis thaliana Columbia (Col-0) plants and Pieris brassicae caterpillars were used as a biological system to study the effects of light quality manipulations on VOC emissions and attraction of herbivores. VOCs were analysed using gas chromatography-mass spectrometry and the effects of light quality, notably the red : far red light ratio (R : FR), on expression of genes associated with VOC production were studied using reverse transcriptase-quantitative PCR. The emissions of both constitutive and methyl-jasmonate-induced green leaf volatiles and terpenoids were partially suppressed under low R : FR and severe shading conditions. Accordingly, the VOC-based preference of neonates of the specialist lepidopteran herbivore P. brassicae was significantly affected by the R : FR ratio. We conclude that VOC-mediated interactions among plants and between plants and organisms at higher trophic levels probably depend on light alterations caused by nearby vegetation. Studies on plant-plant and plant-insect interactions through VOCs should take into account the light quality within dense stands when extrapolating to natural and agricultural field conditions.

Molecular nature of mutations induced by high-LET irradiation with argon and carbon ions in Arabidopsis thaliana.

Linear energy transfer (LET) is an important parameter to be considered in heavy-ion mutagenesis. However, in plants, no quantitative data are available on the molecular nature of the mutations induced with high-LET radiation above 101-124keVµm(-1). In this study, we irradiated dry seeds of Arabidopsis thaliana with Ar and C ions with an LET of 290keVµm(-1). We analyzed the DNA alterations caused by the higher-LET radiation. Mutants were identified from the M(2) pools. In total, 14 and 13 mutated genes, including bin2, egy1, gl1, gl2, hy1, hy3-5, ttg1, and var2, were identified in the plants derived from Ar- and C-ions irradiation, respectively. In the mutants from both irradiations, deletion was the most frequent type of mutation; 13 of the 14 mutated genes from the Ar ion-irradiated plants and 11 of the 13 mutated genes from the C ion-irradiated plants harbored deletions. Analysis of junction regions generated by the 2 types of irradiation suggested that alternative non-homologous end-joining was the predominant pathway of repair of break points. Among the deletions, the proportion of large deletions (>100bp) was about 54% for Ar-ion irradiation and about 64% for C-ion irradiation. Both current results and previously reported data revealed that the proportions of the large deletions induced by 290-keVµm(-1) radiations were higher than those of the large deletions induced by lower-LET radiations (6% for 22.5-30.0keVµm(-1) and 27% for 101-124keVµm(-1)). Therefore, the 290keVµm(-1) heavy-ion beams can effectively induce large deletions and will prove useful as novel mutagens for plant breeding and analysis of gene functions, particularly tandemly arrayed genes.

Expression of OsSPY and 14-3-3 genes involved in plant height variations of ion-beam-induced KDML 105 rice mutants.

The culm length of two semidwarf rice mutants (PKOS1, HyKOS1) obtained from low-energy N-ion beam bombardments of dehusked Thai jasmine rice (Oryza sativa L. cv. KDML 105) seeds showed 25.7% and 21.5% height reductions and one spindly rice mutant (TKOS4) showed 21.4% increase in comparison with that of the KDML 105 control. A cDNA-RAPD analysis identified differential gene expression in internode tissues of the rice mutants. Two genes identified from the cDNA-RAPD were OsSPY and 14-3-3, possibly associated with stem height variations of the semidwarf and spindly mutants, respectively. The OsSPY gene encoded the SPY protein which is considered to be a negative regulator of gibberellin (GA). On the other hand, the 14-3-3 encoded a signaling protein which can bind and prevent the RSG (repression of shoot growth) protein function as a transcriptional repressor of the kaurene oxidase (KO) gene in the GA biosynthetic pathway. Expression analysis of OsSPY, 14-3-3, RSG, KO, and SLR1 was confirmed in rice internode tissues during the reproductive stage of the plants by semi-quantitative RT-PCR technique. The expression analysis showed a clear increase of the levels of OsSPY transcripts in PKOS1 and HyKOS1 tissue samples compared to that of the KDML 105 and TKOS4 samples at the age of 50-60 days which were at the ages of internode elongation. The 14-3-3 expression had the highest increase in the TKOS4 samples compared to those in KDML 105, PKOS1 and HyKOS1 samples. The expression analysis of RSG and KO showed an increase in TKOS4 samples compared to that of the KDML 105 and that of the two semidwarf mutants. These results indicate that changes of OsSPY and 14-3-3 expression could affect internode elongation and cause the phenotypic changes of semidwarf and spindly rice mutants, respectively.

Differential gene expression in pepper (Capsicum annuum) exposed to UV-B.

In the present paper, complementary DNA-amplified fragment length polymorphism (cDNA-AFLP) was used to examine and identify differentially expressed genes in Capsicum annuum exposed to UV-B irradiation. Around 4000 transcript derived fragments (TDFs) were visualized and in total 183 TDFs were isolated, sequenced and analyzed by Blast 2 go. Among these TDFs, 84 of them showed homology to known genes. There were 43 TDFs showing up-regulated expression, 24 TDFs showing down-regulated expression and 29 TDFs showing both up-regulated and down-regulated expression, respectively. Some of these TDFs were found to be in response/related to UV-B stress, including carbonic anhydrase, calcium-dependent protein, thionin-like protein, bzip protein and so on. In particular, chlorophyll a/b binding protein (Capcab) responding to UV-B stress was cloned. It was concluded that Capcab could play a protective role in plant anti-UV-B and maintaining photosynthetic rate under UV-B stress.

Transcriptome sequencing revealed the influence of blue light on the expression levels of light-stress response genes in Centella asiatica.

Centella asiatica is rich in medical and cosmetic properties. While physiological responses of C. asiatica to light have been widely reported, the knowledge of the effects of light on its gene expression is sparse. In this study, we used RNA sequencing (RNA-seq) to investigate the expression of the C. asiatica genes in response to monochromatic red and blue light. Most of the differentially expressed genes (DEGs) under blue light were up-regulated but those under red light were down-regulated. The DEGs encoded for CRY-DASH and UVR3 were among up-regulated genes that play significant roles in responses under blue light. The DEGs involved in the response to photosystem II photodamages and in the biosynthesis of photoprotective xanthophylls were also up-regulated. The expression of flavonoid biosynthetic DEGs under blue light was up-regulated but that under red light was down-regulated. Correspondingly, total flavonoid content under blue light was higher than that under red light. The ABI5, MYB4, and HYH transcription factors appeared as hub nodes in the protein-protein interaction network of the DEGs under blue light while ERF38 was a hub node among the DEGs under red light. In summary, stress-responsive genes were predominantly up-regulated under blue light to respond to stresses that could be induced under high energy light. The information obtained from this study can be useful to better understand the responses of C. asiatica to different light qualities.

Genetic polymorphisms in mutagenesis progeny of Arabidopsis thaliana irradiated by carbon-ion beams and γ-rays irradiations.

Purpose: Heavy-ion beams and γ-rays are popular physical mutagenesis to generate mutations in higher plants. It has been found that they show different mutation frequencies and spectrums of phenotype induction, however, the characteristics of heavy-ion beams on genetic polymorphism have not been clarified by comparing with γ-rays.Materials and methods: In the present study, seeds of Arabidopsis thaliana were exposed to carbon-ion beams (with linear energy transfer (LET) of 50 keV/µm) and γ-rays (with average LET of 0.2 keV/µm) irradiation. By using inter-simple sequence repeat (ISSR) and random amplified polymorphic DNA (RAPD) analysis, the genetic polymorphism of both M1 and M3 plants were investigated, respectively.Results: Carbon-ion beams induced relatively higher polymorphism rate in both M1 and M3 generation than γ-rays: the polymorphism rates of M1 plants derived from carbon-ion beams irradiation are 12.87% (ISSR-C) and 9.01% (RAPD-C), while are 7.67% (ISSR-γ) and 1.45% (RAPD-γ) of plants derived from γ-rays. In M3 generation, the polymorphism rates of ISSR-C, RAPD-C, ISSR-γ, and RAPD-γ are 17.64%, 22.79%, 12.10%, and 2.82%, respectively.Conclusions: In summary, the exposure to carbon-ion beams and γ-rays lead to the change of genomic DNA of A. thaliana, which could be tested in M1 plants and M3 plants by ISSR and RAPD technology. So, both carbon-ion beams and γ-rays can induce variations of genetic polymorphisms in M1 plants and M3 plants. The genetic polymorphisms of M1 plants and M3 plants induced by carbon-ion beams are higher than γ-rays, indicating that heavy-ion beams irradiations mutation breeding is more advantageous than conventional ionizing radiations. Average molecular polymorphism of M1 plants is lower than M3 mutants, by nearly 4.77% (ISSR-C), 13.78% (RAPD-C), 4.43% (ISSR-γ), and 1.37% (RAPD-γ). We hope our study will provide basic information for understanding the effects of carbon-ion beams and γ-rays for plant mutation breeding.

A UV-B-responsive glycosyltransferase, OsUGT706C2, modulates flavonoid metabolism in rice.

Although natural variations in rice flavonoids exist, and biochemical characterization of a few flavonoid glycosyltransferases has been reported, few studies focused on natural variations in tricin-lignan-glycosides and their underlying genetic basis. In this study, we carried out metabolic profiling of tricin-lignan-glycosides and identified a major quantitative gene annotated as a UDP-dependent glycosyltransferase OsUGT706C2 by metabolite-based genome-wide association analysis. The putative flavonoid glycosyltransferase OsUGT706C2 was characterized as a flavonoid 7-O-glycosyltransferas in vitro and in vivo. Although the in vitro enzyme activity of OsUGT706C2 was similar to that of OsUGT706D1, the expression pattern and induced expression profile of OsUGT706C2 were very different from those of OsUGT706D1. Besides, OsUGT706C2 was specifically induced by UV-B. Constitutive expression of OsUGT706C2 in rice may modulate phenylpropanoid metabolism at both the transcript and metabolite levels. Furthermore, overexpressing OsUGT706C2 can enhance UV-B tolerance by promoting ROS scavenging in rice. Our findings might make it possible to use the glycosyltransferase OsUGT706C2 for crop improvement with respect to UV-B adaptation and/or flavonoid accumulation, which may contribute to stable yield.

Signalling cascades integrating light-enhanced nitrate metabolism.

In higher plants, light is crucial for regulation of nitrate uptake, translocation and assimilation into organic compounds. Part of this metabolism is tightly coupled to photosynthesis because the enzymes involved, nitrite reductase and glutamate synthase, are localized to the chloroplasts and receive reducing power from photosynthetic electron transport. However, important enzymes in nitrate acquisition and reduction are localized to cellular compartments other than chloroplasts and are also up-regulated by light, i.e. transporters in cell and organellar membranes and nitrate reductase in the cytosol. This review describes the different light-dependent signalling cascades regulating nitrate metabolism at the transcriptional as well as post-transcriptional level, and how reactions in different compartments of the cell are co-ordinated. Essential players in this network are phytochrome and HY5 (long hypocotyls 5)/HYH (HY5 homologue)-dependent signalling pathways, the energy-related AMPK (AMP-activated protein kinase) protein kinase homologue SNRK1 (sucrose non-fermenting kinase 1-related kinase), chloroplastic thioredoxins and the prokaryotically originated PII protein. A complex light-dependent network of regulation emerges, which appears to be necessary for optimal nitrogen assimilation and for avoiding the accumulation of toxic intermediates and side products, such as nitrite and reactive oxygen compounds.

The response profile to chronic radiation exposure based on the transcriptome analysis of Scots pine from Chernobyl affected zone.

Radioactive contamination of the natural areas is one of the most long-lasting anthropogenic impacts on the environment. Scots pine (Pinus sylvestris L.) is a promising organism for radiation-related research because of its high radiosensitivity, but the genome size of Pinacea species has imposed obstacles for high-throughput studies so far. In this work, we conducted the analysis of the de novo assembled transcriptome of Scots pine populations growing in the Chernobyl-affected zone, which is still today contaminated with radionuclides because of the accident at the nuclear power plant in 1986. The transcriptome profiles indicate a clear pattern of adaptive stress response, which seems to be dose-dependent. The transcriptional response indicates a continuous modulation of the cellular redox system, enhanced expression of chaperones and histones, along with the control of ions balance. Interestingly, the activity of transposable element families is inversely correlated to the exposure levels to radiation. These adaptive responses, which are triggered by radiation doses 30 times lower than the one accepted as a safe for biota species by international regulations, suggest that the environmental management in radiation protection should be reviewed.

Reduction of geomagnetic field (GMF) to near null magnetic field (NNMF) affects some Arabidopsis thaliana clock genes amplitude in a light independent manner.

Plant endogenous clock consists of self-sustained interlocked transcriptional/translational feedback loops whose oscillation regulates many circadian processes, including gene expression. Its free running rhythm can be entrained by external cues, which can influence all clock parameters. Among external cues, the geomagnetic field (GMF) has been demonstrated to influence plant growth and development. We evaluated the quantitative expression (qRT-PCR) of three clock genes (LHY, GI and PRR7) in time-course experiments under either continuous darkness (CD) or long days (LD) conditions in Arabidopsis thaliana seedlings exposed to GMF (∼40 µT) and Near Null Magnetic Field (NNMF; ∼40 nT) conditions. Under both LD and CD conditions, reduction of GMF to NNMF prompted a significant increase of the gene expression of LHY and PRR7, whereas an opposite trend was found for GI gene expression. Exposure of Arabidopsis to NNMF altered clock gene amplitude, regardless the presence of light, by reinforcing the morning loop. Our data are consistent with the existence of a plant magnetoreceptor that affects the Arabidopsis endogenous clock.

Characterization of cis-acting elements in light regulation of the nuclear gene encoding the A subunit of chloroplast isozymes of glyceraldehyde-3-phosphate dehydrogenase from Arabidopsis thaliana.

We have characterized cis-acting elements involved in light regulation of the nuclear gene (GapA) encoding the A subunit of chloroplast glyceraldehyde-3-phosphate dehydrogenase (GAPDH) in Arabidopsis thaliana. Our results show that a 1.1-kb promoter fragment of the GapA gene is sufficient to confer light inducibility and organ specificity in transgenic Nicotiana tabacum (tobacco) plants, using the beta-glucuronidase gene of Escherichia coli as the reporter gene. Deletion analysis indicates that the -359 to -110 bp region of the GapA gene is necessary for light responsiveness. Within this region there are three copies of a decamer repeat (termed the Gap box) having the consensus sequence 5'-CAAATGAA(A/G)A-3', which has not been characterized in the promoter regions of other light-regulated genes. A deletion (to -247) producing loss of one copy of these elements from the GapA promoter reduces light induction by two- to threefold compared with a promoter deletion (to -359) with all three Gap boxes present, while deletion of all three Gap boxes (to -110) abolishes light induction completely. Gel mobility shift experiments using tobacco nuclei as the source of nuclear proteins show that GapA promoter fragments that contain these repeats bind strongly to a factor in the nuclear extract and that binding can be abolished by synthetic competitors consisting only of a monomer or dimer of the Gap box. Furthermore, a trimer, dimer, and monomer of the Gap box show binding activity and, like the authentic GapA promoter-derived probes, show binding activities that are correlated with Gap box copy number. These results strongly suggest that these repeats play important roles in light regulation of the GapA gene of A. thaliana.

Knockout of glutelin genes which form a tandem array with a high level of homology in rice by gamma irradiation.

In the course of evolution, a gene is often duplicated in tandem, resulting in a functional redundancy. The analysis of function of these genes by raising double mutant might be difficult because they are very tightly linked. We described here a mutant of such a tandem duplicated gene. glu1 is a gamma-ray-induced rice mutant, which lacks an acidic subunit of glutelin, a major seed storage protein. We found that glu1 harbors a 129.7-kb deletion involving two highly similar and tandem repeated glutelin genes, GluB5 and GluB4. The deletion eliminated the entire GluB5 and GluB4 gene except half of the first exon of GluB5. GluB5 and GluB4 have the same amino acid sequence in the acidic subunit, suggesting that only the mutation involving both GluB5 and GluB4 results in the lack of the glutelin acidic subunit deleted in glu1. Our finding suggests that gamma-ray can be an effective mutagen to analyze tandem repeated and functionally redundant genes.

Differential expression of 10 sweetpotato peroxidases in response to sulfur dioxide, ozone, and ultraviolet radiation.

Secretory class III plant peroxidase (POD, EC 1.11.1.7) is believed to function in diverse physiological processes, including responses to various environmental stresses. To understand the function of each POD in terms of air pollutants and UV radiation, changes in POD activity and expression of 10 POD genes isolated from cell cultures of sweetpotato (Ipomoea batatas) were investigated in the leaves of sweetpotato after treatment with sulfur dioxide (SO(2) 500ppb, 8h/day for 5 days), ozone (O(3) 200ppb, 8h/day for 6 days), and ultraviolet radiation (UV-B 0.6mWm(-2) for 24h, UV-C 0.16mWm(-2) for 24h). All treatments significantly reduced the PSII photosynthetic efficiency (F(v)/F(m)). POD-specific activities (units/mg protein) were increased in leaves treated with SO(2) and O(3) by 5.2- and 7.1-fold, respectively, compared to control leaves. UV-B and UV-C also increased POD activities by 3.0- and 2.4-fold, respectively. As determined by RT-PCR analysis, 10 POD genes showed differential expression patterns upon treatment with air pollutants and UV radiation. Among the POD genes, swpa1, swpa2, and swpa4 were strongly induced following each of the treatments. Interestingly, basic POD genes (swpb1, swpb2, and swpb3) were highly expressed following SO(2) treatment only, whereas neutral swpn1 was highly induced following O(3) treatment only. These results indicated that some specific POD isoenzymes might be specifically involved in the defense mechanism against oxidative stress induced by air pollutants and UV radiation in sweetpotato plants.

Transcriptome analysis reveals fundamental differences in plant response to acute and chronic exposure to ionizing radiation.

We analyzed the influence of acute and chronic ionizing radiation (IR) on plant genome stability and global genome expression. Plants from the "chronic" group were grown for 21 days on (137)Cs-artificially contaminated soil, and received a cumulative dose of 1Gy. The "acute" plant group was exposed to an equal dose of radiation delivered as a single pulse. Analysis of homologous recombination (HR) events revealed a significantly higher increase in HR frequency (HRF) in the "chronic" group as compared to "acute" group. To understand the observed difference we performed global genome expression analysis. RNA profiling at 2h and 24h after acute irradiation showed two-third of up- and down-regulated genes to be similarly regulated at both time points. In contrast, less than 10% of the genes up- or down-regulated at 2h or 24h post-acute irradiation were similarly changed after chronic exposure. Promoter analysis revealed substantial differences in the specific regulatory elements found in acute and chronic transcriptomes. Further comparison of the data with existing profiles for several stresses, including UVC and heavy metals, showed substantial transcriptome similarities with the acute but not the chronic transcriptome. Plants exposed to chronic but not acute radiation showed early flowering; transcriptome analysis also revealed induction of flowering genes in "chronic" group.

Transmissible and nontransmissible mutations induced by irradiating Arabidopsis thaliana pollen with gamma-rays and carbon ions.

An early genetic study showed that most radiation-induced mutations are not transmitted to progeny. In recent molecular studies in plants, mainly M2 plants or their progeny, which contain only transmissible mutations, have been analyzed, but the early results imply that these studies are insufficient as comprehensive descriptions of radiation-induced mutations. To study radiation-induced mutations caused by low-LET gamma-rays and high-LET carbon ions at the molecular level, we used the pollen-irradiation method and the plant Arabidopsis thaliana to study various mutations, including nontransmissible mutations. This analysis revealed that most mutants induced with irradiation with gamma-rays (150-600 Gy) or carbon ions (40-150 Gy) carried extremely large deletions of up to >6 Mbp, the majority of which were not transmitted to progeny. Mutations containing 1- or 4-bp deletions, which were transmitted normally, were also found. Comparison of the deleted regions in the mutants showing various manners of transmission suggests that the nontransmissibility of the large deletions may be due to the deletion of a particular region that contains a gene or genes required for gamete development or viability.