Molecular cloning of Arabidopsis photolyase gene (PHR1) and characterization of its promoter region

det1-1-induced UV-C hyposensitivity through UVR3 and PHR1 photolyase gene over-expression

Obligate photoautotrophs such as plants must capture energy from sunlight and are therefore exposed to the damaging collateral effects of ultraviolet (UV) irradiation, especially on DNA. Here we investigated the interconnection between light signaling and DNA repair, two concomitant pathways during photomorphogenesis, the developmental transition associated with the first light exposure. It is shown that combination of an enhanced sunscreen effect and photoreactivation confers a greater level of tolerance to damaging UV-C doses in the constitutive photomorphogenic de-etiolated1-1 (det1--1) Arabidopsis mutant. In darkness, expression of the PHR1 and UVR3 photolyase genes, responsible for photoreactivation, is maintained at a basal level through the positive action of HY5 and HYH photomorphogenesis-promoting transcription factors and the repressive effects of DET1 and COP1. Upon light exposure, HY5 and HYH activate PHR1 gene expression while the constitutively expressed nuclear-localized DET1 protein exerts a strong inhibitory effect. Altogether, the data presented indicate a dual role for DET1 in controlling expression of light-responsive and DNA repair genes, and describe more precisely the contribution of photomorphogenic regulators in the control of light-dependent DNA repair.

An unidentified ultraviolet-B-specific photoreceptor mediates transcriptional activation of the cyclobutane pyrimidine dimer photolyase gene in plants

Cyclobutane pyrimidine dimers (CPDs) constitute a majority of DNA lesions caused by ultraviolet-B (UVB). CPD photolyase, which rapidly repairs CPDs, is essential for plant survival under sunlight containing UVB. Our earlier results that the transcription of the cucumber CPD photolyase gene (CsPHR) was activated by light have prompted us to propose that this light-driven transcriptional activation would allow plants to meet the need of the photolyase activity upon challenges of UVB from sunlight. However, molecular mechanisms underlying the light-dependent transcriptional activation of CsPHR were unknown. In order to understand spectroscopic aspects of the plant response, we investigated the wavelength-dependence (action spectra) of the light-dependent transcriptional activation of CsPHR. In both cucumber seedlings and transgenic Arabidopsis seedlings expressing reporter genes under the control of the CsPHR promoter, the action spectra exhibited the most predominant peak in the long-wavelength UVB waveband (around 310 nm). In addition, a 95-bp cis-acting region in the CsPHR promoter was identified to be essential for the UVB-driven transcriptional activation of CsPHR. Thus, we concluded that the photoperception of long-wavelength UVB by UVB photoreceptor(s) led to the induction of the CsPHR transcription via a conserved cis-acting element.

ROLLED LEAF 9, encoding a GARP protein, regulates the leaf abaxial cell fate in rice

Leaves, the collective organ produced by the shoot apical meristem (SAM), are polarized along their adaxial-abaxial axis. In this study, we characterized two rice (Oryza sativa) allelic rolled-leaf mutants, rolled leaf 9-1 (rl9-1) and rl9-2, which display very similar phenotypes with completely adaxialized leaves and malformed spikelets. We cloned the RL9 gene by way of a map-based cloning strategy. Molecular studies have revealed that RL9 encodes a GARP protein, an orthologue of Arabidopsis KANADIs. RL9 is mainly expressed in roots, leaves, and flowers. The transient expression of a RL9-GFP (green fluorescent protein) fusion protein has indicated that RL9 protein is localized in the nucleus, suggesting that RL9 acts as a putative transcription factor.

CPD photolyase gene from Spinacia oleracea: repair of UV-damaged DNA and expression in plant organs

The UV-B radiation contained in solar radiation has deleterious effects on plant growth, development and physiology. Specific damage to DNA caused by UV radiation involves the cyclobutyl pyrimidine dimers (CPD) and the pyrimidine (6-4) pyrimidone photoproducts. CPDs are repaired by CPD photolyase via a UV-A/blue light-dependent mechanism. The gene for the class II CPD photolyase has been cloned from higher plants such as Arabidopsis, cucumbers and rice. We isolated and characterized the cDNA and a genomic clone encoding the spinach class II CPD photolyase. The gene consisted of 3777 bases and 9 exons. The sequence of amino acids predicted from the nucleotide sequence of the cDNA of the gene was highly homologous to that of the higher plants listed above. When a photolyase-deficient Escherichia coli strain was transformed with the cDNA, photoreactivation activity was partially restored, by the illumination with photoreactivating light, resulting in an increased survival and decreased content of CPDs in the Escherichia coli genome. In both the male and female plants, the gene was highly expressed in leaves and flowers under the condition of 14-h light and 10-h dark cycle. The expression in the roots was quite low compared with the other organs.

A gene for a Class II DNA photolyase from Oryza sativa: cloning of the cDNA by dilution-amplification

Ultraviolet radiation induces the formation of two classes of photoproducts in DNA-the cyclobutane pyrimidine dimer (CPD) and the pyrimidine [6-4] pyrimidone photoproduct (6-4 product). Many organisms produce enzymes, termed photolyases, which specifically bind to these lesions and split them via a UV-A/blue light-dependent mechanism, thereby reversing the damage. These photolyases are specific for either CPDs or 6-4 products. Two classes of photolyases (class I and class II) repair CPDs. A gene that encodes a protein with class II CPD photolyase activity in vitro has been cloned from several plants including Arabidopsis thaliana, Cucumis sativus and Chlamydomonas reinhardtii. We report here the isolation of a homolog of this gene from rice (Oryza sativa), which was cloned on the basis of sequence similarity and PCR-based dilution-amplification. The cDNA comprises a very GC-rich (75%) 5; region, while the 3; portion has a GC content of 50%. This gene encodes a protein with CPD photolyase activity when expressed in E. coli. The CPD photolyase gene encodes at least two types of mRNA, formed by alternative splicing of exon 5. One of the mRNAs encodes an ORF for 506 amino acid residues, while the other is predicted to code for 364 amino acid residues. The two RNAs occur in about equal amounts in O. sativa cells.

Genomic Structure of the Cucumber CPD Photolyase Gene

Light-dependent transcriptional activation of the photolyase gene imparts UVB tolerance to a plant. In the present study, the cucumber CPD photolyase gene (CsPHR) was isolated from a genomic DNA library and its genomic structure was scrutinized. As a result, putative light-responsive cis-acting elements were found in the CsPHR promoter.

An ultraviolet-B-resistant mutant with enhanced DNA repair in Arabidopsis

An ultraviolet-B (UV-B)-resistant mutant, uvi1 (UV-B insensitive 1), of Arabidopsis was isolated from 1,280 M(1) seeds that had been exposed to ion beam irradiation. The fresh weight of uvi1 under high-UV-B exposure was more than twice that of the wild type. A root-bending assay indicated that root growth was less inhibited by UV-B exposure in uvi1 than in the wild type. When the seedlings were grown under white light, the UV-B dose required for 50% inhibition was about 6 kJ m(-2) for the wild type and 9 kJ m(-2) for uvi1. When the seedlings were irradiated with UV-B in darkness, the dose required for 50% inhibition was about 1.5 kJ m(-2) for the wild type and 4 kJ m(-2) for uvi1. An enzyme-linked immunosorbent assay showed that the reduction in levels of cyclobutane pyrimidine dimers (CPDs) under white light and of (6-4) photoproducts in darkness occurred faster in uvi1 than in the wild type. These results indicate that uvi1 had increased photoreactivation of CPDs and dark repair of (6-4) photoproducts, leading to strong UV-B resistance. Furthermore, the transcript levels of PHR1 (CPD photolyase gene) were much higher in uvi1 than in the wild type both under white light and after UV-B exposure. Placing the plants in the dark before UV-B exposure decreases the early reduction of CPDs in the wild type but not in uvi1. Our results suggest that UVI1 is a negative regulator of two independent DNA repair systems.

A comparison of the effects of DNA-damaging agents and biotic elicitors on the induction of plant defense genes, nuclear distortion, and cell death

Pea (Pisum sativum L. cv Alcan) endocarp tissue challenged with an incompatible fungal pathogen, Fusarium solani f. sp. phaseoli or fungal elicitors results in the induction of pathogenesis-related (PR) genes and the accumulation of pisatin, a phytoalexin. Essentially the same response occurs in pea tissue exposed to DNA-specific agents that crosslink or intercalate DNA. In this study, the effects of DNA-damaging agents were assessed relative to the inducible expression of several pea PR genes: phenylalanine ammonia lyase, chalcone synthase, and DRR206. Mitomycin C and actinomycin D mimicked the biotic elicitors in enhancing the expression of all three PR genes. The activities of these PR gene promoters, isolated from different plants, were evaluated heterologously in transgenic tobacco. It is remarkable that beta-glucuronidase expression was induced when plants containing the heterologous phenylalanine ammonia lyase, chalcone synthase, and DRR206 promoter-beta-glucuronidase chimeric reporter genes were treated by DNA-damaging agents. Finally, cytological analyses indicated that many of these agents caused nuclear distortion and collapse of the treated pea cells. Yet we observed that cell death is not necessary for the induction of the PR gene promoters assessed in this study. Based on these observations and previously published results, we propose that DNA damage or the associated alteration of chromatin can signal the transcriptional activation of plant defense genes.