UV-B Tolerance Research Articles

Amplification of abiotic stress tolerance potential in rice seedlings with a low dose of UV-B seed priming.

UV-B radiation is a major abiotic stress factor that adversely affects the growth and productivity of crop plants including rice (Oryza sativa L.). However, on the other hand, lower doses of UV-B radiation applied to seeds can have a priming effect on plants emerging from it. In this study, seeds of O. sativa var. kanchana were primed with UV-B radiation (6 kJ m-2) and were further subjected to NaCl, polyethylene glycol 6000 (PEG) and UV-B stress. The effects of UV-B priming in imparting NaCl, PEG and UV-B stress tolerance to rice seedlings were analysed through various photosynthetic features and antioxidative mechanisms. PSI and PSII activity levels as well as chl a fluorescence were found to be significantly higher in the UV-B primed and unstressed seedlings. When stress (NaCl, PEG and high UV-B) was imposed, increased PSI and PSII activity levels, chl a fluorescence and metabolite accumulation (proline, total phenolics and sugar) as well as nonenzymatic (ascorbate and glutathione) and enzymatic (superoxide dismutase, catalase, ascorbate peroxidase) antioxidants were recorded in UV-B primed and NaCl-stressed plants followed by UV-B primed and UV-B-stressed plants, and primed and PEG-stressed, compared with unprimed and stressed conditions. The results indicate that UV-B priming in rice seedlings effectively enhances the NaCl stress tolerance potential in rice to a greater extent than UV-B and PEG stress tolerance potential. The cost-effectiveness of UV-B seed priming is predominantly clear from the differing tolerance responses of rice seedlings exposed to different stress conditions.

Reprint of Efficient fungal UV-screening provides a remarkably high UV-B tolerance of photosystem II in lichen photobionts

Lichen photobionts in situ have an extremely UV-B tolerant photosystem II efficiency (Fv/Fm). We have quantified the UV-B-screening offered by the mycobiont and the photobiont separately. The foliose lichens Nephroma arcticum and Umbilicaria spodochroa with 1: intact or 2: removed cortices were exposed to 0.7 Wm-2 UV-BBE for 4 h. Intact thalli experienced no reduction in Fv/Fm, whereas cortex removal lowered Fv/Fm in exposed photobiont layers by 22% for U. spodochroa and by 14% for N. arcticum. We also gave this UV-B dose to algal cultures of Coccomyxa and Trebouxia, the photobiont genera of N. arcticum and U. spodochroa, respectively. UV-B caused a 56% reduction in Fv/Fm for Coccomyxa, and as much as 98% in Trebouxia. The fluorescence excitation ratio (FER) technique comparing the fluorescence from UV-B or UV-A-excitation light with blue green excitation light using a Xe-PAM fluorometer showed that these photobiont genera did not screen any UV-B or UV-A The FER technique with a Multiplex fluorometer estimated the UV-A screening of isolated algae to be 13–16%, whereas intact lichens screened 92–95% of the UV-A. In conclusion, the cortex of N. arcticum and U. spodochroa transmitted no UV-B and little UV-A to the photobiont layer beneath. Thereby, the upper lichen cortex forms an efficient fungal solar radiation screen providing a high UV-B tolerance for studied photobionts in situ. By contrast, isolated photobionts have no UV-B screening and thus depend on their fungal partners in nature.

Efficient fungal UV-screening provides a remarkably high UV-B tolerance of photosystem II in lichen photobionts

Lichen photobionts in situ have an extremely UV-B tolerant photosystem II efficiency (Fv/Fm). We have quantified the UV-B-screening offered by the mycobiont and the photobiont separately. The foliose lichens Nephroma arcticum and Umbilicaria spodochroa with 1: intact or 2: removed cortices were exposed to 0.7 Wm-2 UV-BBE for 4 h. Intact thalli experienced no reduction in Fv/Fm, whereas cortex removal lowered Fv/Fm in exposed photobiont layers by 22% for U. spodochroa and by 14% for N. arcticum. We also gave this UV-B dose to algal cultures of Coccomyxa and Trebouxia, the photobiont genera of N. arcticum and U. spodochroa, respectively. UV-B caused a 56% reduction in Fv/Fm for Coccomyxa, and as much as 98% in Trebouxia. The fluorescence excitation ratio (FER) technique comparing the fluorescence from UV-B or UV-A-excitation light with blue green excitation light using a Xe-PAM fluorometer showed that these photobiont genera did not screen any UV-B or UV-A The FER technique with a Multiplex fluorometer estimated the UV-A screening of isolated algae to be 13–16%, whereas intact lichens screened 92–95% of the UV-A. In conclusion, the cortex of N. arcticum and U. spodochroa transmitted no UV-B and little UV-A to the photobiont layer beneath. Thereby, the upper lichen cortex forms an efficient fungal solar radiation screen providing a high UV-B tolerance for studied photobionts in situ. By contrast, isolated photobionts have no UV-B screening and thus depend on their fungal partners in nature.

UVR8-mediated induction of flavonoid biosynthesis for UVB tolerance is conserved between the liverwort Marchantia polymorpha and flowering plants.

Damaging UVB radiation is a major abiotic stress facing land plants. In angiosperms the UV RESISTANCE LOCUS8 (UVR8) photoreceptor coordinates UVB responses, including inducing biosynthesis of protective flavonoids. We characterised the UVB responses of Marchantia polymorpha (marchantia), the model species for the liverwort group of basal plants. Physiological, chemical and transcriptomic analyses were conducted on wild-type marchantia exposed to three different UVB regimes. CRISPR/Cas9 was used to obtain plant lines with mutations for components of the UVB signal pathway or the flavonoid biosynthetic pathway, and transgenics overexpressing the marchantia UVR8 sequence were generated. The mutant and transgenic lines were analysed for changes in flavonoid content, their response to UVB exposure, and transcript abundance of a set of 48 genes that included components of the UVB response pathway characterised for angiosperms. The marchantia UVB response included many components in common with Arabidopsis, including production of UVB-absorbing flavonoids, the central activator role of ELONGATED HYPOCOTYL5 (HY5), and negative feedback regulation by REPRESSOR OF UV-B PHOTOMORPHOGENESIS1 (RUP1). Notable differences included the greater importance of CHALCONE ISOMERASE-LIKE (CHIL). Mutants disrupted in the response pathway (hy5) or flavonoid production (chalcone isomerase, chil) were more easily damaged by UVB. Mutants (rup1) or transgenics (35S:MpMYB14) with increased flavonoid content had increased UVB tolerance. The results suggest that UVR8-mediated flavonoid induction is a UVB tolerance character conserved across land plants and may have been an early adaptation to life on land.

Abstract 4020: Hyaluronan fragments as inflammation mediators in the early stages of melanomagenesis

Abstract UV light exposure is the main risk factor for melanoma development. Skin is constantly exposed to UV light, which induces the formation of reactive oxygen species (ROS). ROS are able to degrade hyaluronan (HA), the main extracellular matrix component of the skin epidermis. HA participates in several biological and pathological processes like in inflammation and cancer. It is postulated that in skin an intact HA coat around the cells has a protective effect against UV-radiation, while HA fragments derived from HA degradation are biologically active and may have tumor promoting effects. The aim of the present work was to study the role of HA fragments in melanomagenesis. Does pericellular hyaluronan or its degradation products affect UVB tolerance, melanocyte viability, intracellular signaling and the expression of proinflammatory cytokines? In our experimental model, primary human melanocytes were pretreated with Streptomyces hyaluronidase (Strept. Hyal) for 10 min to degrade the pericellular HA coat and thereafter exposed to UVB (30 mJ/cm2). After the UVB exposure Strept. Hyal was added again to accelerate HA degradation and HA fragment accumulation. The expression levels of proinflammatory cytokines were determined using qRT-PCR. Signaling pathways activated after UVB exposure were studied by western blotting. Cell viability was examined and the influences of UVB and HA coat degradation on cell cycle and apoptosis were analyzed with FACS. In this study, we show that UVB induces the expression of the proinflammatory cytokines IL-1β and IL6 and the chemoattractant cytokines IL8 and CXCL-10. This induction was strongly elevated by the Strept. Hyal treatment suggesting that HA fragments produced by HA degradation are responsible for upregulation of these genes. The inhibition of p38 and NFkβ reversed the effect of UVB + Strept. Hyal treatment on IL6 and IL8 expression indicating that this signaling pathway is responsible for the upregulation of these genes. Moreover, silencing of hyaluronan synthase 2 (Has2) was also able to block the effect of UVB + Strept. Hyal on the studied genes suggesting that the fragmentation of endogenously produced HA generates biologically active, proinflammatory signals. Interestingly, blocking CD44, the main hyaluronan receptor, expression with siRNA was ineffective, suggesting that other upstream effectors than CD44 are involved. Regarding cell viability and apoptosis the Strept. Hyal –treatment showed only a slight difference compared to the UVB –treated melanocytes. Taken together, our results demonstrate that HA fragments strengthen the inflammatory response induced by UVB exposure. UVB + Strept. Hyal activated the p38-NFkβ signaling pathway causing the upregulation of proinflammatory cytokines. The present data suggest that HA fragments mediate sustained inflammation, which may be a trigger for tumor formation. Citation Format: Piia Takabe, Leena Rauhala, Markku Tammi, Raija Tammi, Sanna Pasonen-Seppänen. Hyaluronan fragments as inflammation mediators in the early stages of melanomagenesis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4020.

Comparison of UV-B tolerance between wild-type and albino Japanese flounder Paralichthys olivaceus juveniles

Comparison of UV-B tolerance between wild-type and albino Japanese flounder Paralichthys olivaceus juveniles

Riboflavin induces Metarhizium spp. to produce conidia with elevated tolerance to UV-B, and upregulates photolyases, laccases and polyketide synthases genes.

The effect of nutritional supplementation of two Metarhizium species with riboflavin (Rb) during production of conidia was evaluated on (i)conidial tolerance (based on germination) to UV-B radiation and on (ii)conidial expression following UV-B irradiation, of enzymes known to be active in photoreactivation, viz., photolyase (Phr), laccase (Lac) and polyketide synthase (Pks). Metarhizium acridum (ARSEF 324) and Metarhizium robertsii (ARSEF 2575) were grown either on (i) potato dextrose agar medium (PDA), (ii) PDA supplemented with 1% yeast extract (PDAY), (iii) PDA supplemented with Rb (PDA+Rb), or (iv) PDAY supplemented with Rb (PDAY+Rb). Resulting conidia were exposed to 866·7mWm-2 of UV-B Quaite-weighted irradiance to total doses of 3·9 or 6·24kJm-2 . Some conidia also were exposed to 16klux of white light (WL) after being irradiated, or not, with UV-B to investigate the role of possible photoreactivation. Relative germination of conidia produced on PDA+Rb (regardless Rb concentration) or on PDAY and exposed to UV-B was higher compared to conidia cultivated on PDA without Rb supplement, or to conidia suspended in Rb solution immediately prior to UV-B exposure. The expression of MaLac3 and MaPks2 for M. acridum, as well as MrPhr2, MrLac1, MrLac2 and MrLac3 for M.robertsii was higher when the isolates were cultivated on PDA+Rb and exposed to UV-B followed by exposure to WL, or exposed to WL only. Rb in culture medium increases the UV-B tolerance of M.robertsii and M. acridum conidia, and which may be related to increased expression of Phr, Lac and Pks genes in these conidia. The enhanced UV-B tolerance of Metarhizium spp. conidia produced on Rb-enriched media may improve the effectiveness of these fungi in biological control programs.

Effects of long-term UV-exposure and plant sex on the leaf phenoloxidase activities and phenolic concentrations of Salix myrsinifolia (Salisb.)

The accumulation of flavonoids on the leaf surface is a well-characterized protective mechanism against UV-B radiation. Other protective mechanisms, such as the induction of antioxidative enzymes and peroxidase-mediated lignification may also be important. The effects of UV-B radiation have mainly been considered in short-term studies, whereas ecologically more relevant long-term field studies are still rare. Here we examined the effects of long-term exposure to enhanced UV-B radiation on the activities of two antioxidative enzymes, polyphenol oxidase (PPO; EC 1.10.2.2 and EC 1.14.18.1) and guaiacol peroxidase (POD; EC 1.11.1.7), as well as the phenolic concentrations in two sexes of the dioecious species, Salix myrsinifolia. After three consecutive growth seasons with enhanced UV-B radiation, we found that PPO activity was decreased by UV radiation in male plants, which might explain their lower UV-B tolerance when compared to female plants. In addition, male plants had higher specific activity than did female plants under ambient conditions, supporting the idea that males of S. myrsinifolia are generally more growth-oriented than females. By contrast, neither UV treatment nor sex had significant effects on the POD activities of willows. Gender differences in the concentrations of phenolic compounds are in line with the general concept that males are less well defended than females. We suggest that the inability to increase PPO and POD activity, along with lower accumulation of UV-B absorbing compounds under UV-B exposure, might be one of the reasons why males had thinner leaves and were less tolerant of UV-B than were females.

UV-B induced biosynthesis of a novel sunscreen compound in solar radiation and desiccation tolerant cyanobacteria.

The small-molecule sunscreen compounds, mycosporine-like amino acids (MAAs), have strong ultraviolet (UV) absorption and can protect cyanobacteria against UV-B damage. However, the molecular mechanism underlying UV-B signaling and MAA chemical diversity remain largely unclear. Here, we identified a five-gene cluster for MAA biosynthesis in the solar radiation and desiccation tolerant cyanobacterium Nostoc flagelliforme. A LuxR family protein OrrA was identified as a positive UV-B responsive regulator binding to the promoter region of this gene cluster. OrrA functions as an activator mediating the UV-B induced MAA biosynthesis. Overexpression of orrA strengthened its UV-B tolerance during desiccation, and enhanced the photosynthetic recovery upon rehydration. Heterologous expression of this gene cluster in Anabaena PCC 7120 produces the same MAA as that in field samples of N. flagelliforme. The MAA structure is assigned as mycosporine-2-(4-deoxygadusolyl-ornithine) with a molecular weight of 756 Da, the structurally unique MAA compound reported to date. This MAA was catalyzed by mysD-mysC2-mysC1 encoding proteins from 4-deoxygadusol, which was synthesized through the catalysis of mysA-mysB products. Thus, we elucidated the transcriptional mechanism for a novel type MAA biosynthesis in solar radiation and desiccation tolerant cyanobacteria, which shed light on the identification of other components for UV-B signaling in cyanobacteria.

The imprints of the high light and UV-B stresses in Oryza sativa L. ‘Kanchana’ seedlings are differentially modulated

High light and ultraviolet-B radiation (UV-B) are generally considered to have negative impact on photosynthesis and plant growth. The present study evaluates the tolerance potential of three cultivars of Oryza sativa L. (Kanchana, Mattatriveni and Harsha) seedlings towards high light and UV-B stress on the basis of photosynthetic pigment degradation, chlorophyll a fluorescence parameters and rate of lipid peroxidation, expressed by malondialdehyde content. Surprisingly, it was revealed that Kanchana was the most sensitive cultivar towards high light and at the same time it was the most tolerant cultivar towards UV-B stress. This contrasting feature of Kanchana towards high light and UV-B tolerance was further studied by analyzing photosystem (PS) I and II activity, mitochondrial activity, chlorophyll a fluorescence transient, enzymatic and non-enzymatic antioxidant defense system. Due to the occurrence of more PS I and PSII damages, the inhibition of photochemical efficiency and emission of dissipated energy as heat or fluorescence per PSII reaction center was higher upon high light exposure than UV-B treatments in rice seedlings of Kanchana. The mitochondrial activity was also found to be drastically altered upon high light as compared to UV-B treatments. The UV-B induced accumulation of non-enzymatic antioxidants (proline, total phenolics, sugar and ascorbate) and enzymatic antioxidants (ascorbate peroxidase, guaiacol peroxidase, superoxide dismutase and glutathione reductase) in rice seedlings than those subjected to high light exposure afforded more efficient protection against UV-B radiation in rice seedlings. Our results proved that high tolerance of Kanchana towards UV-B than high light treatments, correlated linearly with the protected photosynthetic and mitochondrial machinery which was provided by upregulation of antioxidants particularly by total phenolics, ascorbate and ascorbate peroxidase in rice seedlings. Data presented in this study conclusively proved that rice cultivar Kanchana respond to different environmental signals independently and tolerance mechanisms to individual stress factors was also varied.

Differentially evolved glucosyltransferases determine natural variation of rice flavone accumulation and UV-tolerance

Decoration of phytochemicals contributes to the majority of metabolic diversity in nature, whereas how this process alters the biological functions of their precursor molecules remains to be investigated. Flavones, an important yet overlooked subclass of flavonoids, are most commonly conjugated with sugar moieties by UDP-dependent glycosyltransferases (UGTs). Here, we report that the natural variation of rice flavones is mainly determined by OsUGT706D1 (flavone 7-O-glucosyltransferase) and OsUGT707A2 (flavone 5-O-glucosyltransferase). UV-B exposure and transgenic evaluation demonstrate that their allelic variation contributes to UV-B tolerance in nature. Biochemical characterization of over 40 flavonoid UGTs reveals their differential evolution in angiosperms. These combined data provide biochemical insight and genetic regulation into flavone biosynthesis and additionally suggest that adoption of the positive alleles of these genes into breeding programs will likely represent a potential strategy aimed at producing stress-tolerant plants.

Expression of the UVR8 photoreceptor in different tissues reveals tissue-autonomous features of UV-B signalling.

The Arabidopsis UV-B photoreceptor UV RESISTANCE LOCUS 8 (UVR8) orchestrates the expression of hundreds of genes, many of which can be associated with UV-B tolerance. UV-B does not efficiently penetrate into tissues, yet UV-B regulates complex growth and developmental responses. To unravel to what extent and how UVR8 located in different tissues contributes to UV-B-induced responses, we expressed UVR8 fused to the YELLOW FLUORESCENT PROTEIN (YFP) under the control of tissue-specific promoters in a uvr8 null mutant background. We show that (1) UVR8 localized in the epidermis plays a major role in regulating cotyledon expansion, and (2) expression of UVR8 in the mesophyll is important to protect adult plants from the damaging effects of UV-B. We found that UV-B induces transcription of selected genes, including the key transcriptional regulator ELONGATED HYPOCOTYL 5 (HY5), only in tissues that express UVR8. Thus, we suggest that tissue-autonomous and simultaneous UVR8 signalling in different tissues mediates, at least partly, developmental and defence responses to UV-B.

Evaluation of virulence, tolerance to environmental factors and antimicrobial activities of entomopathogenic fungi against two-spotted spider mite, Tetranychus urticae

The two-spotted spider mite, Tetranychus urticae, is an important pest. This mite has recently become a serious problem due to the continuous use of acaricides, resulting in resistance. Thus, there is a need to identify alternative control methods to suppress spider mite populations. We screened pathogenic fungi for the control of spider mites using multiple tools to assess virulence and fitness under various environmental conditions. Twelve selected fungal isolates demonstrated the virulence against mites, and their thermotolerance, UV-B tolerance and cold tolerance varied by isolate. The most optimal fungi to control mites were selected based on results that took various tested environmental factors into consideration. Additionally, the antimicrobial activities of the selected fungi were assessed to explore the potential for the dual control of not only mites but also plant pathogens. Antimicrobial activities against both the bacterium Bacillus cereus and the fungus Botrytis cinerea were observed simultaneously in 8 fungal isolates. These results suggested that the fungal isolates Lecanicillium attenuatum 4-1 and Purpureocillium lilacinum 2R-4-6 can be used in an eco-friendly control program against the two-spotted spider mite and Beauveria bassiana s.l. 2R-4-5 and Metarhizium anisopliae s.l. 4-2 would be powerful candidates for the dual control of pests and diseases.

PH as a key factor defining the niche space of the alpine crustacean species Daphnia tanakai

AbstractUnderstanding the mechanisms of adaptation of alpine aquatic organisms to the alpine environment, one of the ecosystems most vulnerable to climate change, would help us predict how those organisms would respond to the upcoming climate change. Here, we examined how one of Japan's endemic crustaceans, Daphnia tanakai, which has been found only in alpine lakes and pools in high mountain moors, is adapted to the alpine environment and what restricts its distribution only to the alpine environment. Lab experiments on UVB tolerance and growth rate under different pH and temperature based on the field survey for pools in mountain moors revealed that D. tanakai was differentiated from two low‐altitude species (Daphnia dentifera and Daphnia pulicaria) by its tolerance to low pH such as 4.5, which is equal to the mean pH of pools in the high mountain moors occupied by D. tanakai. The growth rate at pH 4.5 was, however, significantly lower than that at higher pH, suggesting that low pH was not necessarily an optimal condition, and that other factors restrict the distribution to alpine lakes. Vulnerability to invertebrate predators such as Chaoborus was suggested as such a factor by additional experiments on swimming activity and predation and the fact that D. tanakai has only been found in pools without Chaoborus. Because it is known that the pH of alpine lakes is tightly linked with temperature, global warming may diminish the advantage of D. tanakai and allow invasion of alpine lakes by unwelcome predators and competitors from lower altitudes.

Relative sensitivity of DNA and photosystem II in Ulva intestinalis (Chlorophyta) under natural solar irradiation

High intensities of sunlight can result in DNA and photosystem II (PSII) damage. However, the relative sensitivity of both these targets under natural sunlight and especially over a long period has not been studied in algae so far. Although DNA damage is highly specifically induced by ultraviolet-B radiation (UVB, 280-315 nm), PSII is inactivated by a broad spectrum. The green macroalga Ulva intestinalis is an appropriate and interesting study organism with which to investigate the relative importance of the 2 different targets of sunlight because this alga contains no UV-screening protective pigments, although it is exposed to strong solar irradiation in its natural habitat. This entails a high risk of DNA damage. Therefore, diel time courses and long-term development of DNA damage and the optimal quantum yield of PSII (F-v/F-m) were studied in situ. F-v/F-m was extremely reduced at noon, but a fast recovery was observed in the afternoon. As dark-adapted basal fluorescence (F-o) of PSII was substantially decreased during the day, non-photochemical quenching is suggested to be a key photoprotective strategy in U. intestinalis. In contrast, even in samples with strongly reduced F-v/F-m, only very low DNA damage was found, irrespective of the accumulated UVB dose. We propose that efficient photoreactivation driven by natural sunlight balances the induction of dimers. This leads to a higher UVB tolerance of DNA than that observed in algae under experimental UVB irradition. In this field study, U. intestinalis suffered more from photoinhibition than from DNA damage.

COP1 is required for UV-B–induced nuclear accumulation of the UVR8 photoreceptor

The UV-B photoreceptor UV RESISTANCE LOCUS 8 (UVR8) promotes UV-B acclimation and tolerance in Arabidopsis thaliana UVR8 localizes to both cytosol and nucleus, but its main activity is assumed to be nuclear. UV-B photoreception stimulates nuclear accumulation of UVR8 in a presently unknown manner. Here, we show that CONSTITUTIVELY PHOTOMORPHOGENIC 1 (COP1) is required for UV-B-induced nuclear accumulation of UVR8, but bypassing the COP1 requirement for UVR8 nuclear accumulation did not rescue the cop1 mutant UV-B phenotype. Using a glucocorticoid receptor (GR)-based fusion protein system to conditionally localize GR-UVR8 to the nucleus, we have demonstrated that both photoactivation and nuclear localization of UVR8 are required for UV-B-induced photomorphogenic responses. In contrast, there was no UV-B response when UV-B-activated UVR8 was artificially retained in the cytosol. In agreement with a predominantly nuclear activity, constitutively active UVR8(W285A) accumulated in the nucleus also in the absence of UV-B. Furthermore, GR-COP1 expression lines suggested that UV-B-activated UVR8 can be coimported into the nucleus by COP1. Our data strongly support localization of UVR8 signaling in the nucleus and a dual role for COP1 in the regulation of UV-B-induced UVR8 nuclear accumulation and in UVR8-mediated UV-B signaling.

The Na+ /H+ antiporter Nhx1 controls vacuolar fusion indispensible for life cycles in vitro and in vivo in a fungal insect pathogen.

The sole Na+ /H+ antiporter Nhx1 has been generally unexplored in filamentous fungi. We characterized Nhx1 in the entomopathogenic fungus Beauveria bassiana. An eGFP-tagged Nhx1 fusion accumulated in small punctuate structures, presumably endosomal and trans-Golgi network compartments, between septum and tubular vacuole of each wild-type cell stained with a vacuole-specific dye. Deletion of nhx1 resulted in significant acidification and severe fusion defect in vacuoles, which were fragmented and distinct from large or tubular wild-type vacuoles. The deletion also caused a drastic reduction in aerial conidiation or submerged blastospore production and more severe defect in vegetative growth than in conidial germination. The Δnhx1 mutant became more sensitive to high osmolarity, heat shock and several metal ions during growth but its conidia showed increased UV-B tolerance. Intriguingly, Δnhx1 was unable to infect a model insect through cuticle penetration or intrahaemocoel injection because it produced much less biomass and cuticle-degrading enzymes in a minimal broth and failed to form blastospores in the insect haemolymph. All changes were completely or largely restored by targeted nhx1 complementation. Our results provide novel insight into an indispensability of Nhx1 for not only vacuolar fusion but also life cycles in vitro and in vivo in B. bassiana.

Ultraviolet-B-induced DNA damage and ultraviolet-B tolerance mechanisms in species with different functional groups coexisting in subalpine moorlands.

High doses of ultraviolet-B (UV-B; 280-315 nm) radiation can have detrimental effects on plants, and especially damage their DNA. Plants have DNA repair and protection mechanisms to prevent UV-B damage. However, it remains unclear how DNA damage and tolerance mechanisms vary among field species. We studied DNA damage and tolerance mechanisms in 26 species with different functional groups coexisting in two moorlands at two elevations. We collected current-year leaves in July and August, and determined accumulation of cyclobutane pyrimidine dimer (CPD) as UV-B damage and photorepair activity (PRA) and concentrations of UV-absorbing compounds (UACs) and carotenoids (CARs) as UV-B tolerance mechanisms. DNA damage was greater in dicot than in monocot species, and higher in herbaceous than in woody species. Evergreen species accumulated more CPDs than deciduous species. PRA was higher in Poaceae than in species of other families. UACs were significantly higher in woody than in herbaceous species. The CPD level was not explained by the mechanisms across species, but was significantly related to PRA and UACs when we ignored species with low CPD, PRA and UACs, implying the presence of another effective tolerance mechanism. UACs were correlated negatively with PRA and positively with CARs. Our results revealed that UV-induced DNA damage significantly varies among native species, and this variation is related to functional groups. DNA repair, rather than UV-B protection, dominates in UV-B tolerance in the field. Our findings also suggest that UV-B tolerance mechanisms vary among species under evolutionary trade-off and synergism.

Positional mapping and identification of novel quantitative trait locus responsible for UV-B radiation tolerance in soybean [Glycine max (L.) Merr.

The amount of ultraviolet-B radiation (UV-B: 280–320 nm) reaching Earth’s surface is expected to increase due to stratospheric ozone depletion. This could cause significant biological damage in plants, and serious yield losses in crops. Soybean [Glycine max (L.) Merr.], a major legume crop, is known to be sensitive to UV-B radiation. Thus, developing a UV-B-tolerant soybean is an efficient and economical strategy to avoid putative yield losses through increased UV-B irradiation. The objective of this study is to identify the novel quantitative trait loci (QTLs) for UV-B tolerance in the soybean using high-density genetic linkage mapping. One hundred and fifteen F8-derived F12 recombinant inbred lines developed from a cross between the UV-B susceptible cultivar, Keunol, and a tolerant breeding line, Iksan 10, were used. Three categories of phenotypic traits were scored: degree of leaf color change, degree of leaf shape change and degree of total plant damage. A genome-wide molecular genetic linkage map containing 8691 single nucleotide polymorphism markers was constructed using the recently developed genotyping platform, the 180K Axiom SoyaSNP assay. Using composite interval mapping analysis, one major candidate QTL on chromosome 7 was identified and designated qUVBT1, and is located between two flanking makers, AX-90437826 and AX-90317546, within 1.6 cM, corresponding to a ~24-kb physical region with six annotated gene models. One of them is a homolog of yeast RAD23, which has previously been reported to be a UV excision repair protein. This result could be valuable in breeding new UV-B-tolerant soybean cultivars and elucidating the UV-B response mechanism in soybean plants.

Screening and evaluation of entomopathogenic fungi against the green peach aphid, Myzus persicae, using multiple tools

The green peach aphid, Myzus persicae Sulzer, is an important pest that infests more than 40 families of plant and has become a serious problem due to its high resistance to insecticides. To address this problem, interest in entomopathogenic fungi as biocontrol agents in the context of integrated pest management strategies has increased. In this study, we report the efficient screening of entomopathogenic fungi for control of the green peach aphid through the evaluation of environmental factors as well as virulence. Initial screening based on pathogenicity against the green peach aphid was performed using 342 isolates of entomopathogenic fungi from Korea. Twenty different entomopathogenic fungi were isolated from green peach aphid cadavers supporting fungal conidiation. These isolates were identified by microscopic examination, genetic sequencing of the ITS region, and universally primed PCR (UP-PCR) as follows: 3 isolates of Lecanicillium attenuatum, 9 isolates of Beauveria bassiana, 1 isolate of Metarhizium anisopliae, 1 isolate of Metarhizium flavoviride, 5 isolates of Purpureocillium lilacinum, and 1 isolate of Aspergillus sp. Further virulence and environmental factors such as thermotolerance, UV-B tolerance, and cold activity were evaluated simultaneously to select 20 isolates because the importance of environmental factors in the development of bioinsecticides is greatly increasing. Virulence and environmental factor activities varied based on the fungal isolate. Purpureocillium lilacinum SD17 was selected as the most likely candidate for a biocontrol agent against the green peach aphid based on a relative comparison of its activities, including virulence.