UV-B Induces Chloroplast Movements in a Phototropin-Dependent Manner

We examined the impact of UV-B irradiation on chloroplast movements in Arabidopsis leaves. Directional chloroplast movements induced by blue light have been described in multiple plant species. In weak light, chloroplasts accumulate at periclinal cell walls to increase light capture. In strong light, chloroplasts exhibit the avoidance response, as they move towards anticlinal walls to protect the photosynthetic apparatus from light-induced damage. In Arabidopsis, chloroplast movements are triggered by phototropins, phot1 and phot2, which are known as blue/UV-A photoreceptors. We found that irradiation with UV-B of 3.3 µmol·m−2·s−1 induced chloroplast accumulation in wild-type plants. UV-B-triggered accumulation was dependent on the presence of phototropins, especially phot1, but not on UVR8 (the canonical UV-B photoreceptor). Irradiation with strong UV-B of 20 µmol·m−2·s−1 did not induce substantial chloroplast relocations in wild-type leaves. However, in the jac1 mutant, which is defective in chloroplast accumulation, strong UV-B elicited chloroplast avoidance. This indicated that UV-B can also activate signaling to the avoidance response. To assess the possibility of indirect effects of UV-B on chloroplast movements, we examined the impact of UV-B on the actin cytoskeleton, which serves as the motile system for chloroplast movements. While irradiation with UV-B of 3.3 µmol·m−2·s−1 did not affect the actin cytoskeleton, strong UV-B disrupted its structure as shown using an Arabidopsis line expressing Lifeact-green fluorescent protein (GFP). In wild-type plants, pretreatment with strong UV-B attenuated chloroplast responses triggered by subsequent blue light irradiation, further indicating that this UV-B intensity also indirectly affects chloroplast movements. Taken together, our results suggest that the effect of UV-B on chloroplast movement is twofold: it directly induces phototropin-mediated movements; however, at higher intensities, it attenuates the movements in a nonspecific manner

6,4–PP Photolyase Encoded by AtUVR3 is Localized in Nuclei, Chloroplasts and Mitochondria and its Expression is Down-Regulated by Light in a Photosynthesis-Dependent Manner

search input Abstract Pyrimidine dimers are the most important DNA lesions induced by UVB irradiation. They can be repaired directly by photoreactivation or indirectly by the excision repair pathways. Photoreactivation is carried out by photolyases, enzymes which bind to the dimers and use the energy of blue light or UVA to split bonds between adjacent pyrimidines. Arabidopsis thaliana has three known photolyases: AtPHR1, AtCRY3 and AtUVR3. Little is known about the cellular localization and regulation of AtUVR3 expression. We have found that its transcript level is down-regulated by light (red, blue or white) in a photosynthesis-dependent manner. The down-regulatory effect of red light is absent in mature leaves of the phyB mutant, but present in leaves of phyAphyB. UVB irradiation does not increase AtUVR3 expression in leaves. Transiently expressed AtUVR3–green fluorescent protein (GFP) is found in the nuclei, chloroplasts and mitochondria of Nicotiana benthamiana epidermal cells. In the nucleoplasm, AtUVR3–GFP is distributed uniformly, while in the nucleolus it forms speckles. Truncated AtUVR3 and muteins were used to identify the sequences responsible for its subcellular localization. Mitochondrial and chloroplast localization of AtUVR3 is independent of its N-terminal sequence. Amino acids located at the C-terminal loop of the protein are involved in its transport into chloroplasts and its retention inside the nucleolus

DNA structures decorated with cathepsin G/secretory leukocyte proteinase inhibitor stimulate IFNI production by plasmacytoid dendritic cells

Plasmacytoid dendritic cells (pDCs) and neutrophils are detected in psoriatic skin lesions and implicated in the pathogenesis of psoriasis. pDCs specialize in the production of type I interferon (IFNI), a cytokine that plays an important role in chronic autoimmune-like inflammation, including psoriasis. Here, we demonstrate that IFNI production in pDCs is stimulated by DNA structures containing the neutrophil serine protease cathepsin G (CatG) and the secretory leukocyte protease inhibitor (SLPI), which is a controlling inhibitor of serine proteases. We also demonstrate the presence of neutrophil-derived DNA structures containing CatG and SLPI in lesional skin samples from psoriasis patients. These findings suggest a previously unappreciated role for CatG in psoriasis by linking CatG and its inhibitor SLPI to the IFNI-dependent regulation of immune responses by pDCs in psoriatic skin

Ocena częstości występowania hipoglikemii w zależności od aktywności fizycznej

  Aim. Assessment of the effect of the physical activity level in diabetic patients on the occurrence of hypo­glycaemia. Material and methods. The survey was conducted in a group of 422 diabetic patients: 209 patients with type 1 diabetes mellitus (129 women, 80 men, mean age 30 ± 11 years, mean duration of diabetes 12 ± 8 years, HbA1c: 7.5 ± 1.4%) and 213 patients with type 2 diabetes mellitus (119 women, 94 men, mean age 60 ± 12 years, mean duration of diabetes 10 ± 9 years, HbA1c: 8 ± 1.5%). Patients filled in the questionnaire covering data on diabetes control and physical activity (based on the International Physical Activity Question­naire — IPAQ). Results. Overall the number of patients with hypogly­cemia was significantly higher in patients with high physical activity (65%) when compared to low activity (43%; p &lt; 0.01). Patients with moderate activity did not differ from remaining groups. In type 1 diabetes mellitus number of episodes was significantly lower in low activity group (4%) when compared to high activity (61%; p &lt; 0.001) and moderate activity (17%; p &lt; 0.001). Also significant difference was found be­tween high and moderate activity (p &lt; 0.001). In type 2 diabetes mellitus the relation was similar. 23% patients with hypoglycemia in high activity; 11% in moder­ate activity (p &lt; 0.005) and 5% in low activity group (p &lt; 0.001 vs. high and moderate activity respectively). Conclusions. The incidence of hypoglycaemia increases along with increasing physical activity. This indicates the necessity of an increased education in patients planning physical activity.   Cel. Ocena wpływu poziomu aktywności fizycznej u chorych na cukrzycę na występowanie hipoglikemii. Materiał i metody. Badanie zostało przeprowadzone w grupie 422 pacjentów chorych na cukrzycę: 209 chorych na cukrzycę typu 1 (129 kobiet, 80 mężczyzn, średni wiek: 30 ± 11 lat, średni czas trwania cukrzy­cy: 12 ± 8 lat, HbA1c: 7,5 ± 1,4%) oraz 213 chorych na cukrzycę typu 2 (119 kobiet, 94 mężczyzn, średni wiek: 60 ± 12 lat, średni czas trwania cukrzycy: 10 ± 9 lat, HbA1c: 8 ± 1,5%). Pacjenci uzupełnili ankietę obejmującą dane dotyczące wyrównania cukrzycy oraz aktywności fizycznej (wg Międzynarodowego Kwestio­nariusza Aktywności Fizycznej — IPAQ). Wyniki. Ogółem liczba pacjentów z hipoglikemią była istotnie wyższa u pacjentów cechujących się wysoką aktywnością fizyczną (65%) w porównaniu z niską aktywnością (43%, p < 0,01). Pacjenci z umiarkowa­ną aktywnością nie różnili się od pozostałych grup. W przypadku cukrzycy typu 1 liczba epizodów była istotnie niższa w grupie o niskiej aktywności (4%) w porównaniu z wysoką aktywnością (61%, p < 0,001) i umiarkowaną aktywnością (17%, p < 0,001). Stwierdzono również istotną różnicę pomiędzy wysoką i umiarkowaną aktywnością (p < 0,001). U chorych na cukrzycę typu 2 relacja była podobna: 23% pacjentów z hipoglikemią w przypadku wysokiej aktywności, 11% — w umiarkowanej (p < 0,005) i 5% w grupie o niskiej aktywności (odpowiednio p < 0,001 vs. wy­soka i umiarkowana aktywność). Wnioski. Częstość występowania hipoglikemii zwiększa się wraz ze wzrostem aktywności fizycznej. Wskazuje to na konieczność zwiększenia edukacji pacjentów planujących aktywność fizyczną

Fine tuning chloroplast movements through physical interactions between phototropins

Phototropins are plant photoreceptors which regulate numerous responses to blue light, including chloroplast relocation. Weak blue light induces chloroplast accumulation, whereas strong light leads to an avoidance response. Two Arabidopsis phototropins are characterized by different light sensitivities. Under continuous light, both can elicit chloroplast accumulation, but the avoidance response is controlled solely by phot2. As well as continuous light, brief light pulses also induce chloroplast displacements. Pulses of 0.1s and 0.2s of fluence rate saturating the avoidance response lead to transient chloroplast accumulation. Longer pulses (up to 20s) trigger a biphasic response, namely transient avoidance followed by transient accumulation. This work presents a detailed study of transient chloroplast responses in Arabidopsis. Phototropin mutants display altered chloroplast movements as compared with the wild type: phot1 is characterized by weaker responses, while phot2 exhibits enhanced chloroplast accumulation, especially after 0.1s and 0.2s pulses. To determine the cause of these differences, the abundance and phosphorylation levels of both phototropins, as well as the interactions between phototropin molecules are examined. The formation of phototropin homo- and heterocomplexes is the most plausible explanation of the observed phenomena. The physiological consequences of this interplay are discussed, suggesting the universal character of this mechanism that fine-tunes plant reactions to blue light. Additionally, responses in mutants of different protein phosphatase 2A subunits are examined to assess the role of protein phosphorylation in signaling of chloroplast movements

Phototropin2 3’UTR overlaps with the AT5G58150 gene encoding an inactive RLK kinase

ackground This study examines the biological implications of an overlap between two sequences in the Arabidop�sis genome, the 3’UTR of the PHOT2 gene and a putative AT5G58150 gene, encoded on the complementary strand. AT5G58150 is a probably inactive protein kinase that belongs to the transmembrane, leucine-rich repeat receptor-like kinase family. Phot2 is a membrane-bound UV/blue light photoreceptor kinase. Thus, both proteins share their cellular localization, on top of the proximity of their loci. Results The extent of the overlap between 3’UTR regions of AT5G58150 and PHOT2 was found to be 66 bp, using RACE PCR. Both the at5g58150 T-DNA SALK_093781C (with insertion in the promoter region) and 35S::AT5G58150�GFP lines overexpress the AT5G58150 gene. A detailed analysis did not reveal any substantial impact of PHOT2 or AT5G58150 on their mutual expression levels in diferent light and osmotic stress conditions. AT5G58150 is a plasma membrane protein, with no apparent kinase activity, as tested on several potential substrates. It appears not to form homodimers and it does not interact with PHOT2. Lines that overexpress AT5G58150 exhibit a greater reduction in lat‑ eral root density due to salt and osmotic stress than wild-type plants, which suggests that AT5G58150 may partici‑ pate in root elongation and formation of lateral roots. In line with this, mass spectrometry analysis identifed proteins with ATPase activity, which are involved in proton transport and cell elongation, as putative interactors of AT5G58150. Membrane kinases, including other members of the LRR RLK family and BSK kinases (positive regulators of brassinos‑ teroid signalling), can also act as partners for AT5G58150. Conclusions AT5G58150 is a membrane protein that does not exhibit measurable kinase activity, but is involved in signalling through interactions with other proteins. Based on the interactome and root architecture analysis, AT5G58150 may be involved in plant response to salt and osmotic stress and the formation of roots in Arabidopsis

Phototropin interactions with SUMO proteins

The disruption of the sumoylation pathway affects processes controlled by the two phototropins (phots) of Arabidopsis thaliana, phot1 and phot2. Phots, plant UVA/blue light photoreceptors, regulate growth responses and fast movements aimed at optimizing photosynthesis, such as phototropism, chloroplast relocations and stomatal opening. Sumoylation is a posttranslational modification, consisting of the addition of a SUMO (SMALL UBIQUITIN-RELATED MODIFIER) protein to a lysine residue in the target protein. In addition to affecting the stability of proteins, it regulates their activity, interactions and subcellular localization. We examined physiological responses controlled by phots, phototropism and chloroplast movements, in sumoylation pathway mutants. Chloroplast accumulation in response to both continuous and pulse light was enhanced in the E3 ligase siz1 mutant, in a manner dependent on phot2. A significant decrease in phot2 protein abundance was observed in this mutant after blue light treatment both in seedlings and mature leaves. Using plant transient expression and yeast two-hybrid assays, we found that phots interacted with SUMO proteins mainly through their N-terminal parts, which contain the photosensory LOV domains. The covalent modification in phots by SUMO was verified using an Arabidopsis sumoylation system reconstituted in bacteria followed by the mass spectrometry analysis. Lys 297 was identified as the main target of SUMO3 in the phot2 molecule. Finally, sumoylation of phot2 was detected in Arabidopsis mature leaves upon light or heat stress treatment

Influence of Sugars on Blue Light-Induced Chloroplast Relocations

The aim of this study was to investigate the influence of sugars on blue light-induced chloroplast movements. Sucrose and glucose inhibited chloroplast responses in the detached leaves of Arabidopsis thaliana and in Lemna trisulca fronds in a concentration and time-dependent manner. The prolonged exposure necessary for inhibition indicates that sugars may act via altered gene expression. Overexpression of phototropin2, a photoreceptor responsible for the strong blue light response of chloroplasts, counteracted the sugar effect. This may suggest that sugars modify some component(s) of the phototropin2-mediated signal transduction pathway. The expression of PHOT2 was not suppressed by sugars in wild type plants, it was even upregulated by glucose. Impaired chloroplast movements were observed only in mature Arabidopsis plants. The mRNA of SAG12, a late senescence marker, was not detectable in the sugar-incubated leaves. The SAG13 mRNA level and its regulation by sugars were similar in wild type and PHOT2 overexpressor. Thus, the sugar insensitivity of 35S:PHOT2 chloroplast responses was not due to delayed senescence. The sugar-induced transduction pathway involved remains unclear. 3-O-methylglucose did not affect chloroplast movements suggesting the participation of a hexokinase-dependent pathway. Only the amplitude of avoidance response was reduced in gin2-1, a hexokinase1 null mutant. Probably other hexokinases, or glycolysis-associated signals play a role in the suppression of chloroplast responses

All You Need Is Light. Photorepair of UV-Induced Pyrimidine Dimers

Although solar light is indispensable for the functioning of plants, this environmental factor may also cause damage to living cells. Apart from the visible range, including wavelengths used in photosynthesis, the ultraviolet (UV) light present in solar irradiation reaches the Earth&rsquo;s surface. The high energy of UV causes damage to many cellular components, with DNA as one of the targets. Putting together the puzzle-like elements responsible for the repair of UV-induced DNA damage is of special importance in understanding how plants ensure the stability of their genomes between generations. In this review, we have presented the information on DNA damage produced under UV with a special focus on the pyrimidine dimers formed between the neighboring pyrimidines in a DNA strand. These dimers are highly mutagenic and cytotoxic, thus their repair is essential for the maintenance of suitable genetic information. In prokaryotic and eukaryotic cells, with the exception of placental mammals, this is achieved by means of highly efficient photorepair, dependent on blue/UVA light, which is performed by specialized enzymes known as photolyases. Photolyase properties, as well as their structure, specificity and action mechanism, have been briefly discussed in this paper. Additionally, the main gaps in our knowledge on the functioning of light repair in plant organelles, its regulation and its interaction between different DNA repair systems in plants have been highlighted

The Dark Side of UV-Induced DNA Lesion Repair

In their life cycle, plants are exposed to various unfavorable environmental factors including ultraviolet (UV) radiation emitted by the Sun. UV-A and UV-B, which are partially absorbed by the ozone layer, reach the surface of the Earth causing harmful effects among the others on plant genetic material. The energy of UV light is sufficient to induce mutations in DNA. Some examples of DNA damage induced by UV are pyrimidine dimers, oxidized nucleotides as well as single and double-strand breaks. When exposed to light, plants can repair major UV-induced DNA lesions, i.e., pyrimidine dimers using photoreactivation. However, this highly efficient light-dependent DNA repair system is ineffective in dim light or at night. Moreover, it is helpless when it comes to the repair of DNA lesions other than pyrimidine dimers. In this review, we have focused on how plants cope with deleterious DNA damage that cannot be repaired by photoreactivation. The current understanding of light-independent mechanisms, classified as dark DNA repair, indispensable for the maintenance of plant genetic material integrity has been presented