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Plants have evolved adaptations to environmental factors, including UV-B present in solar radiation. Deployment of specific adaptive phenotypes to avoid or repair UV-B damage requires physiological and developmental acclimation to variable UV-B fluence. To gain a better understanding of the events in UV-B acclimation, we have analyzed a 5min to 6h time course of transcriptome and metabolome responses in irradiated and shielded leaves and in immature maize ears to unravel the systemic physiological and developmental responses in exposed and shielded organs. Within 10 min of UV-B exposure, transcripts are changed not only in irradiated leaves, but also in shielded tissues. The number of UV-B-regulated transcripts rapidly increases with exposure length. Interestingly, after 10 min of exposure, the overlap in transcriptome changes in irradiated and shielded organs is significant; while, after 6h of UV-B, most transcripts are specific for each tissue under study. We suggest that early events in all tissues may be elicited by common signaling pathways, while at longer exposure times responses become more organ-specific. Our working hypothesis is that mobile signaling molecules are generated in irradiated organs to elicit the initial responses. We found several metabolites that rapidly change after different treatments during the timecourse; myoinositol is one candidate metabolite based on its rapid modulation in all organs. There is also support from RNA profiling: after 1h UV-B, transcripts for myoinositol-1-phosphate synthase are decreased in both irradiated and shielded leaves suggesting downregulation of biogenesis.

UV-B radiation from normal solar fluence elicits physiological and developmental changes in plants under fluctuating environmental conditions. Most UV photobiology studies in plants utilize controlled greenhouse and growth chamber environments in which few conditions vary except the brief presence of UV-B radiation. Our purpose was to compare responses to UV-B in irradiated and shielded maize organs in field (natural solar plus 2x solar supplementation for defined periods) and greenhouse (2x solar supplementation only) conditions during a 4 hour exposure. Three parameters were assessed -- transcripts, proteins, and metabolites -- to determine the degree of overlap in maize responses in field and greenhouse conditions. We assessed irradiated leaves, and both shielded leaves and immature ears. After comparing transcriptome, proteome and metabolome profiles, we find there are more differences than similarities between field and greenhouse responses.

Ribosomal protein L10 (RPL10) is an ubiquitous protein that participates in joining the 40S and 60S ribosomal subunits into a functional 80S ribosome; however, increasing evidences indicate that RPL10 from various organisms has multiple extra ribosomal functions, besides being a constituent of ribosome and its role in translation. Arabidopsis thalianacontains in its genome three genes encoding RPL10,named RPL10A, RPL10Band RPL10C. Previously, we found that in maize and inA. thaliana, UV-B induces a reduction in protein biosynthesis, probably as a consequence of ribosomal damage; however, cellular recovery occurs in the absence of UV-B. Here, we show that RPL10s are differentially regulated by UV-B in a dosage and time dependent manner: RPL10Cis induced, RPL10B is down regulated at high UV-B intensity, and RPL10Ais not UV-B regulated. In addition, by coimmunoprecipitation studies using RPL10 antibodies and proteins from control and UV-B irradiated Arabidopsis plants, we demonstrate that RPL10associates with different proteins under the two different conditions, including nuclear proteins, suggesting that at least one isoform may have extra-ribosomal roles.

Spontaneous silencing of MuDR/Mu transposons occurs in ~10–100% of the progeny of an active plant, and once silenced reactivation is very rare. To date, only radiation treatments have reactivated silenced Mu; for example UV-B radiation reactivated Mutator activities. Here we have investigated possible mechanisms by which UV-B could reactivate Mu transposons by monitoring transcript abundance, epigenetic DNA marks, and chromatin factors associated with these elements. We demonstrate that both mudrA and B transcripts are expressed at higher levels after an 8 h-UV-B treatment, in both active Mutator and silencing plants, and that different chromatin remodeling events occur in the promoter regions of MuDR than in non-autonomous Mu1 elements. Increased transcript abundance is accompanied by an increase in histone H3 acetylation and by decreased DNA and H3K9me2 methylation. No changes in siRNA levels were detected. In contrast, the decrease in H3K9me2 present at Mu elements after UV-B is significant in silencing plants, suggesting that early changes in H3 methylation in K9, chromatin remodeling, and transcription factor binding contribute directly to transposon reactivation by UV-B in maize.

RNAi knockdown lines targeting two putative chromatin factors (a methyl-CpG-binding domain protein MBD101 and a chromatin remodeling complex protein CHC101) exhibit identical phenotypic consequences after UV-B exposure including necrosis in adult leaves and seedling death. Here we report that these RNAi lines exhibit substantially different transcriptome changes assessed on a 44K Agilent oligonucleotide array platform compared to each other and to UV-B tolerant non-transgenic siblings both before and after 8 h of UV-B exposure. Adult maize leaves express ~26,000 transcript types under greenhouse growth conditions; after 8 h of UV-B exposure 267 transcripts exhibit an expression change in the B73 control line. Most of these transcript abundance changes in B73 after UV-B treatment are not found in the two RNAi knockdown lines: 119 up-regulated transcript types and 128 down-regulated types are uniquely modulated in B73. The mbd101 RNAi line shows many more line-specific transcript changes (897 up, 68 down) than either B73 or the chc101 line (72 up, 103 down). By functional analysis, the largest category of genes with predicted functions affected by UV-B is the DNA/chromatin binding group. Differential activation of suites of transcription factors in the control and transgenic lines are the likely explanation for the divergent transcriptome profiles.

Non-phosphorylating glyceraldehyde- 3-phosphate dehydrogenase (NP-GAPDH) is a conserved cytosolic protein found in higher plants. In photosynthetic cells, the enzyme is involved in a shuttle transfer mechanism to export NADPH from the chloroplast to the cytosol. To investigate the role of this enzyme in plant tissues, we characterized a mutant from Arabidopsis thalianahaving an insertion at the NP-GAPDHgene locus. The homozygous mutant was determined to be null respect to NP-GAPDH, as it exhibited undetectable levels of both transcription of NP-GAPDHmRNA, protein expression and enzyme activity. Transcriptome analysis demonstrated that the insertion mutant plant shows altered expression of several enzymes involved in carbohydrate metabolism. Significantly, cytosolic phosphorylating (NAD-dependent) glyceraldehyde-3-phosphate dehydrogenase mRNA levels are induced in the mutant, which correlates with an increase in enzyme activity. mRNA levels and enzymatic activity of glucose-6-phosphate dehydrogenase were also elevated, correlating with an increase in NADPH concentration. Moreover, increased ROS levels were measured in the mutant plants. Down-regulation of several glycolytic and photosynthetic genes suggests that NP-GAPDH is important for the efficiency of both metabolic processes. The results presented demonstrate that NP-GAPDH has a relevant role in plant growth and development.Non-phosphorylating glyceraldehyde- 3-phosphate dehydrogenase (NP-GAPDH) is a conserved cytosolic protein found in higher plants. In photosynthetic cells, the enzyme is involved in a shuttle transfer mechanism to export NADPH from the chloroplast to the cytosol. To investigate the role of this enzyme in plant tissues, we characterized a mutant from Arabidopsis thalianahaving an insertion at the NP-GAPDHgene locus. The homozygous mutant was determined to be null respect to NP-GAPDH, as it exhibited undetectable levels of both transcription of NP-GAPDHmRNA, protein expression and enzyme activity. Transcriptome analysis demonstrated that the insertion mutant plant shows altered expression of several enzymes involved in carbohydrate metabolism. Significantly, cytosolic phosphorylating (NAD-dependent) glyceraldehyde-3-phosphate dehydrogenase mRNA levels are induced in the mutant, which correlates with an increase in enzyme activity. mRNA levels and enzymatic activity of glucose-6-phosphate dehydrogenase were also elevated, correlating with an increase in NADPH concentration. Moreover, increased ROS levels were measured in the mutant plants. Down-regulation of several glycolytic and photosynthetic genes suggests that NP-GAPDH is important for the efficiency of both metabolic processes. The results presented demonstrate that NP-GAPDH has a relevant role in plant growth and development.

Abstract: Egeria densa, a submersed aquatic species, was exposed to different treatments under UV-B radiation, and the response of phosphoenolpyruvate carboxylase (PEPC) and NADP-malic enzyme (NADP-ME) was determined. Exposure to UV-B radiation for 4 h per day over 7–16 days caused an increase in both enzymes, together with an increase in the activity of some isoforms of several enzymes involved in the antioxidant metabolism, such as superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT) and peroxidase (POD). The content of chlorophylls and carotenoids was considerably decreased, suggesting that degradation or repression of the synthesis of these molecules may be occurring after UV-B exposure. Reactive oxygen species (ROS) were also required for UV-B induction of PEPC and NADP-ME, as the addition of ascorbic acid before UV-B treatment prevented the induction of these enzymes, while salicylic acid was not effective in inducing NADP-ME but increased the expression of the lower molecular mass isoform of PEPC. On the other hand, damage to the photosynthetic machinery may be occurring after exposure to UV-B radiation for 8 per day over 1–2 days, as indicated by a decrease in the levels of Rubisco, PEPC and NADP-ME. Some of the enzymes involved in the antioxidant metabolism, such as CAT and APX, were also sensitive to continuous exposure, evidenced by a decrease in their activity. In this way, in E. densa, several enzymes involved in different metabolic pathways showed a distinct response, depending on the UV-B treatment.

NADP‐malic enzyme (NADP‐ME) is a widely distributed enzyme that catalyzes the oxidative decarboxylation of L‐malate. Photosynthetic NADP‐MEs are found in C4bundle sheath chloroplasts and in the cytosol of CAM plants, while non‐photosynthetic NADP‐MEs are either plastidic or cytosolic in various plants. We propose a classification of plant NADP‐MEs based on their physiological function and localization and we describe recent advances in the characterization of each isoform. Based on the alignment of amino acid sequences of plant NADP‐MEs, we identify putative binding sites for the substrates and analyze the phylogenetic origin of each isoform, revealing several features of the molecular evolution of this ubiquitous enzyme.

NADP-malic enzyme (NADP-ME) is a widely distributed enzyme that catalyzes the oxidative decarboxylation of L-malate. Photosynthetic NADP-MEs are found in C 4bundle sheath chloroplasts and in the cytosol of CAM plants, while non-photosynthetic NADP-MEs are either plastidic or cytosolic in various plants. We propose a classification of plant NADP-MEs based on their physiological function and localization and we describe recent advances in the characterization of each isoform. Based on the alignment of amino acid sequences of plant NADP-MEs, we identify putative binding sites for the substrates and analyze the phylogenetic origin of each isoform, revealing several features of the molecular evolution of this ubiquitous enzyme.

Malate is involved in various metabolic pathways, and there are several enzymes that metabolize it. One important malate metabolizing enzyme is NADP-malic enzyme (NADP-ME). NADP-ME functions in many different pathways in plants, having an important role in C4photosynthesis where it releases the CO2to be used in carbon fixation by Rubisco. Apart from this specialized role, NADP-ME is thought to fulfill diverse housekeeping functions because of its universal presence in different plant tissues. NADP-ME is induced after wounding or exposure to UV-B radiation. In this way, the enzyme is implicated in defense-related deposition of lignin by providing NADPH for the two NADPH-dependent reductive steps in monolignol biosynthesis. On the other hand, it can supply NADPH for flavonoid biosynthesis as many steps in the flavonoid biosynthesis pathway require reductive power. Pyruvate, another product of NADP-ME reaction, can be used for obtaining ATP through respiration in the mitochondria; and may serve as a precursor for synthesis of phosphoenolpyruvate (PEP). PEP is utilized in the shikimate pathway, leading to the synthesis of aromatic amino acids including phenylalanine, the common substrate for lignin and flavonoid synthesis. Moreover, NADP-ME can be involved in mechanisms producing NADPH for synthesis of activated oxygen species that are produced in order to kill or damage pathogens. In conclusion, an increase in the levels of NADP-ME could provide building blocks and energy for biosynthesis of defense compounds, suggesting a role of malate metabolism in plant defense.

ABSTRACTIn this work, we investigated the role of an Arabidopsis protein, AtPDCD5, during senescence after a 24h-dark period. Previously, we demonstrated that AtPDCD5 participates in programmed cell death (PCD) after UV-B exposure and in age-induced senescence. The results presented here, together with previous data, demonstrate that AtPDCD5 not only plays an important role during DNA damage responses induced by UV-B radiation, but also takes part in PCD programs such as dark-induced senescence in Arabidopsis.

UV-B radiation elicits physiological and developmental changes in plants. In this work, to characterize the mechanisms of gene regulation by UV-B radiation, the global miRNA expression profiles in juvenile maize leaves were compared under control conditions in the absence of UV-B and after an 8 h-UV-B treatment similar to ambient UV-B levels using small RNA microarrays. Seventeen miRNAs were identified that were differentially expressed in response to UV-B. In parallel, the expression of putative mRNA targets was examined in mRNA microarrays using the same RNA samples used for the small RNA analysis. In general, there is a strong negative correlation to the miRNA expression. Thus, post-transcriptional regulation is an important step in gene expression by UV-B radiation in maize.

Background Depletion of stratospheric ozone has raised terrestrial levels of ultraviolet-B radiation (UV-B), an environmental change linked to an increased risk of skin cancer and with potentially deleterious consequences for plants. To better understand the processes of UV-B acclimation that result in altered plant morphology and physiology, we investigated gene expression in different organs of maize at several UV-B fluence rates and exposure times.Results Microarray hybridization was used to assess UV-B responses in directly exposed maize organs and organs shielded by a plastic that absorbs UV-B. After 8 hours of high UV-B, the abundance of 347 transcripts was altered: 285 were increased significantly in at least one organ and 80 were downregulated. More transcript changes occurred in directly exposed than in shielded organs, and the levels of more transcripts were changed in adult compared to seedling tissues. The time course of transcript abundance changes indicated that the response kinetics to UV-B is very rapid, as some transcript levels were altered within 1 hour of exposure.Conclusions Most of the UV-B regulated genes are organ-specific. Because shielded tissues, including roots, immature ears, and leaves, displayed altered transcriptome profiles after exposure of the plant to UV-B, some signal(s) must be transmitted from irradiated to shielded tissues. These results indicate that there are integrated responses to UV-B radiation above normal levels. As the same total UV-B irradiation dose applied at three intensities elicited different transcript profiles, the transcriptome changes exhibit threshold effects rather than a reciprocal dose-effect response. Transcriptome profiling highlights possible signaling pathways and molecules for future research.

Background: Depletion of stratospheric ozone has raised terrestrial levels of ultraviolet-B radiation (UV-B), an environmental change linked to an increased risk of skin cancer and with potentially deleterious consequences for plants. To better understand the processes of UV-B acclimation that result in altered plant morphology and physiology, we investigated gene expression in different organs of maize at several UV-B fluence rates and exposure times. Results: Microarray hybridization was used to assess UV-B responses in directly exposed maize organs and organs shielded by a plastic that absorbs UV-B. After 8 hours of high UV-B, the abundance of 347 transcripts was altered: 285 were increased significantly in at least one organ and 80 were downregulated. More transcript changes occurred in directly exposed than in shielded organs, and the levels of more transcripts were changed in adult compared to seedling tissues. The time course of transcript abundance changes indicated that the response kinetics to UV-B is very rapid, as some transcript levels were altered within 1 hour of exposure. Conclusions: Most of the UV-B regulated genes are organ-specific. Because shielded tissues, including roots, immature ears, and leaves, displayed altered transcriptome profiles after exposure of the plant to UV-B, some signal(s) must be transmitted from irradiated to shielded tissues. These results indicate that there are integrated responses to UV-B radiation above normal levels. As the same total UV-B irradiation dose applied at three intensities elicited different transcript profiles, the transcriptome changes exhibit threshold effects rather than a reciprocal dose-effect response. Transcriptome profiling highlights possible signaling pathways and molecules for future research.

The induction of NADP-malic enzyme (NADP-ME) in maize (Zea mays) etiolated seedlings as a function of intensity and duration of exposure to UV-B radiation was investigated by measuring changes in activity and protein, as well as by levels of NADP-ME gene transcripts. Exposures to UV radiation from 2 to 60 min including photon flux densities of UV-B of 0.5–2 mmol quanta m-2 s-1 which are well below levels which occur naturally under full sunlight, caused an increase in Me gene mRNA and NADP-ME protein, as well as in NADP-ME activity. A similar dosage of UV-A radiation was ineffective. A low level of red light (10 µmol quanta m-2 s-1) for only 5 min was also effective in inducing increases in NADP-ME activity equivalent to that with UV-B radiation. A 5 min exposure to far red light (100 µmol quanta m-2 s-1) following UV-B or red light treatment largely reversed the induction of NADP-ME, and this effect of far-red could be eliminated by further treatment with UV-B or red light. These results indicate that physiological levels of UV-B radiation have a positive effect on induction of the synthesis of a photosynthetic enzyme which is involved in C4 photosynthesis. Keywords: C4 photosynthesis, NADP-malic enzyme, UV-B radiation.