Participation of chromatin-remodeling proteins in the repair of ultraviolet-B-damaged DNA.

The genome of plants is organized into chromatin, affecting the rates of transcription, DNA recombination, and repair. In this work, we have investigated the consequences of reduced expression of some chromatin-remodeling factors and histone acetylation in maize (Zea mays) and Arabidopsis (Arabidopsis thaliana) in their participation in DNA repair after ultraviolet (UV)-B irradiation. Plants deficient in NFC102/NFC4 or SDG102/SDG26 showed more damaged DNA than wild-type plants; however, the Arabidopsis chc1 mutant showed similar accumulation of cyclobutane pyrimidine dimers as wild-type plants, in contrast to the increased DNA damage measured in the maize chc101 RNA interference line. In Arabidopsis, plants deficient in chromatin remodeling are also affected in the accumulation of pigments by UV-B. Plants treated with an inhibitor of histone acetyltransferases, curcumin, previous to the UV-B treatment show deficiencies in DNA repair; in addition, the chromatin remodeling-deficient plants have altered levels of acetylated histones after the UV-B treatment, demonstrating that histone acetylation is important during DNA repair in these two plant species. Arabidopsis mutants ham1 and ham2 also showed increased DNA damage after UV-B, suggesting that the role of these proteins in DNA damage repair has been conserved through evolution. However, cyclobutane pyrimidine dimer accumulation was higher in ham1 than in ham2; suggesting that HAM1 has a major role in DNA repair after UV-B. In summary, in this work, we have demonstrated that chromatin remodeling, and histone acetylation in particular, is important during DNA repair by UV-B, demonstrating that both genetic and epigenetic effects control DNA repair in plants.

Transcriptomic, proteomic and metabolomic analysis of UV-B signaling in maize.

BACKGROUND: Under normal solar fluence, UV-B damages macromolecules, but it also elicits physiological acclimation and developmental changes in plants. Excess UV-B decreases crop yield. Using a treatment twice solar fluence, we focus on discovering signals produced in UV-B-irradiated maize leaves that translate to systemic changes in shielded leaves and immature ears. RESULTS: Using transcriptome and proteomic profiling, we tracked the kinetics of transcript and protein alterations in exposed and shielded organs over 6 h. In parallel, metabolic profiling identified candidate signaling molecules based on rapid increase in irradiated leaves and increased levels in shielded organs; pathways associated with the synthesis, sequestration, or degradation of some of these potential signal molecules were UV-B-responsive. Exposure of just the top leaf substantially alters the transcriptomes of both irradiated and shielded organs, with greater changes as additional leaves are irradiated. Some phenylpropanoid pathway genes are expressed only in irradiated leaves, reflected in accumulation of pathway sunscreen molecules. Most protein changes detected occur quickly: approximately 92% of the proteins in leaves and 73% in immature ears changed after 4 h UV-B were altered by a 1 h UV-B treatment. CONCLUSIONS: There were significant transcriptome, proteomic, and metabolomic changes under all conditions studied in both shielded and irradiated organs. A dramatic decrease in transcript diversity in irradiated and shielded leaves occurs between 0 h and 1 h, demonstrating the susceptibility of plants to short term UV-B spikes as during ozone depletion. Immature maize ears are highly responsive to canopy leaf exposure to UV-B.

The sunflower TLDc-containing protein HaOXR2 confers tolerance to oxidative stress and waterlogging when expressed in maize plants.

The sunflower (Helianthus annuus L.) genome encodes six proteins containing a TLDc domain, typical of the eukaryotic OXidation Resistance (OXR) protein family. Expression of sunflower HaOXR2 in Arabidopsis generated plants with increased rosette diameter, higher number of leaves and increased seed production. Maize inbred lines expressing HaOXR2 also showed increased total leaf area per plant. In addition, heterologous expression of HaOXR2 induced an increase in the oxidative stress tolerance in Arabidopsis and maize. Maize transgenic plants expressing HaOXR2 experienced less oxidative damage and exhibited increased photosynthetic performance and efficiency than non-transgenic segregant plants after treatment of leaves with the reactive oxygen species generating compound Paraquat. Expression of HaOXR2 in maize also improved tolerance to waterlogging. The number of expanded leaves, aerial biomass, and stem height and cross-section area were less affected by waterlogging in HaOXR2 expressing plants, which also displayed less aerial tissue damage under these conditions. Transgenic plants also showed an increased production of roots, a typical adaptive stress response. The results show the existence of functional conservation of OXR proteins in dicot and monocot plants and indicate that HaOXR2 could be useful to improve plant performance under conditions that increase oxidative stress.

Maize expressing the sunflower transcription factor HaHB11 has improved productivity in controlled and field conditions.

HaHB11 is a sunflower transcription factor from the homeodomain-leucine zipper I family. Transgenic Arabidopsis plants expressing HaHB11 had larger rosettes and improved seed yield. In this work maize plants from hybrid HiII were transformed with 35S:HaHB11, ZmUBI:HaHB11 and ProHaHB11:HaHB11 and then backcrossed to B73 to obtain a more homozygous inbred phenotype. Transgene expression levels were stable at least during three generations. Greenhouse-grown HaHB11 transgenic lines had larger leaf area and delayed senescence than controls, together with increased total biomass (up to 25%) and seed yield (up to 28%). Field trials conducted with T2 and T4 generations indicated that enhanced leaf area (up to 18%), stem diameter (up to 28%) and total biomass (up to 40%) as well as delayed leaf senescence were maintained among transgenic individuals when upscaling from pots in the greenhouse to communal plants in the field. The T4 field-grown transgenic generation had increased light interception and radiation use efficiency as well as seed yield (43-47% for events driven by the 35S promoter). Results suggest that HaHB11 is a promising tool for crop improvement because differential traits observed in the Arabidopsis model plant were preserved in a crop like maize independently of growth conditions and backcross level.

Transcriptomic, proteomic and metabolomic analysis of maize responses to UV-B: comparison of greenhouse and field growth conditions.

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.

Histone acetylation and chromatin remodeling are required for UV-B-dependent transcriptional activation of regulated genes in maize.

The nuclear proteomes of maize (Zea mays) lines that differ in UV-B tolerance were compared by two-dimensional gel electrophoresis after UV light treatment. Differential accumulation of chromatin proteins, particularly histones, constituted the largest class identified by mass spectrometry. UV-B-tolerant landraces and the B73 inbred line show twice as many protein changes as the UV-B-sensitive b, pl W23 inbred line and transgenic maize expressing RNA interference constructs directed against chromatin factors. Mass spectrometic analysis of posttranslational modifications on histone proteins demonstrates that UV-B-tolerant lines exhibit greater acetylation on N-terminal tails of histones H3 and H4 after irradiation. These acetylated histones are enriched in the promoter and transcribed regions of the two UV-B-upregulated genes examined; radiation-sensitive lines lack this enrichment. DNase I and micrococcal nuclease hypersensitivity assays indicate that chromatin adopts looser structures around the selected genes in the UV-B-tolerant samples. Chromatin immunoprecipitation experiments identified additional chromatin factor changes associated with the nfc102 test gene after UV-B treatment in radiation-tolerant lines. Chromatin remodeling is thus shown to be a key process in acclimation to UV-B, and lines deficient in this process are more sensitive to UV-B.