The Arabidopsis metal tolerance protein AtMTP3 maintains metal homeostasis by mediating Zn exclusion from the shoot under Fe deficiency and Zn oversupply

Zinc ions are required to maintain the biological activity of numerous proteins. However, when mislocalized or accumulated in excess, Zn(2+) ions are toxic because of adventitious binding to proteins and displacement of other metal ions, among them Fe(2+), from their binding sites. Heterologous expression of a previously uncharacterized Arabidopsis thaliana metal tolerance protein, MTP3, in the zrc1 cot1 mutant of budding yeast restores tolerance to, and cellular accumulation of, zinc and cobalt. An MTP3-GFP fusion protein localizes to the vacuolar membrane when expressed in Arabidopsis. Ectopic over-expression of MTP3 increases Zn accumulation in both roots and rosette leaves of A. thaliana, and enhances Zn tolerance. Exposure of wild-type plants to high but non-toxic concentrations of Zn or Co, or Fe deficiency, strongly induce MTP3 expression specifically in epidermal and cortex cells of the root hair zone. Silencing of MTP3 by RNA interference causes Zn hypersensitivity and enhances Zn accumulation in above-ground organs of soil-grown plants and of seedlings exposed to excess Zn or to Fe deficiency. Our data indicate that, in wild-type A. thaliana, the AtMTP3 protein contributes to basic cellular Zn tolerance and controls Zn partitioning, particularly under conditions of high rates of Zn influx into the root symplasm.     

黄瓜MTP基因家族分析及重金属胁迫下表达特征

该研究以模式物种(拟南芥、水稻、玉米)的MTP序列作为种子序列,对黄瓜MTP基因家族(CsMTP)成员进行了系统鉴定和分析;并以Zn2、Cd2+、Mn2+、Cu2+、Fe2+和Mo2+处理后的黄瓜叶片和根系为材料,对CsMTP响应金属离子的表达模式进行了研究,为探究该基因家族对黄瓜重金属胁迫调控机制提供理论依据.结果 ...     

PARL partitions the lipid transfer protein STARD7 between the cytosol and mitochondria

Intramembrane‐cleaving peptidases of the rhomboid family regulate diverse cellular processes that are critical for development and cell survival. The function of the rhomboid protease PARL in the mitochondrial inner membrane has been linked to mitophagy and apoptosis, but other regulatory functions are likely to exist. Here, we identify the START domain‐containing protein STARD7 as an intramitochondrial lipid transfer protein for phosphatidylcholine. We demonstrate that PARL‐mediated cleavage during mitochondrial import partitions STARD7 to the cytosol and the mitochondrial intermembrane space. Negatively charged amino acids in STARD7 serve as a sorting signal allowing mitochondrial release of mature STARD7 upon cleavage by PARL. On the other hand, membrane insertion of STARD7 mediated by the TIM23 complex promotes mitochondrial localization of mature STARD7. Mitochondrial STARD7 is necessary and sufficient for the accumulation of phosphatidylcholine in the inner membrane and for the maintenance of respiration and cristae morphogenesis. Thus, PARL preserves mitochondrial membrane homeostasis via STARD7 processing and is emerging as a critical regulator of protein localization between mitochondria and the cytosol.     

超富集植物对重金属耐受和富集机制的研究进展

超富集植物对重金属耐受和富集机制的研究成为近年来植物逆境生理研究的热点,在简要总结细胞壁沉淀、重金属螯合效应、酶活性机制和细胞区室化作用的基础上,概述了超富集植物对重金属的耐受机制,讨论了重金属跨根细胞质膜运输,共质体内运输、木质部运输和跨叶细胞膜运输的富集过程。     

Potential of efficient and resistant plant growth‐promoting rhizobacteria in lead uptake and plant defence stimulation in Lathyrus sativus under lead stress

• The ability of plant growth‐promoting rhizobacteria (PGPR) to enhance Lathyrus sativus tolerance to lead (Pb) stress was investigated.
• Ten consortia formed by mixing four efficient and Pb‐resistant PGPR strains were assessed for their beneficial effect in improving Pb (0.5 mM) uptake and in inducing the host defence system of L. sativus under hydroponic conditions based on various physiological and biochemical parameters.
• Lead stress significantly decreased shoot (SDW) and root (RDW) dry weight, but PGPR inoculation improved both dry weights, with highest increases in SDW and RDW of plants inoculated with I5 (R. leguminosarum (M5) + P. fluorescens (K23) + Luteibacter sp. + Variovorax sp.) and I9 (R. leguminosarum (M5) + Variovorax sp. + Luteibacter sp. + S. meliloti) by 151% and 94%, respectively. Additionally, inoculation significantly enhanced both chlorophyll and soluble sugar content, mainly in I5 inoculated leaves by 238% and 71%, respectively, despite the fact that Pb decreased these parameters. We also found that PGPR inoculation helps to reduce oxidative damage and enhances antioxidant enzyme activity, phenolic compound biosynthesis, carotenoids and proline content. PGPR inoculation increased Pb uptake in L. sativus, with highest increase in shoots of plants inoculated with I5 and I7, and in roots and nodules of plants inoculated with I1. Moreover, PGPR inoculation enhanced mineral homeostasis for Ca, Cu and Zn under Pb stress, mainly in plants inoculated with I1, I5, I7 and I9.
• Results of our study suggest the potential of efficient and Pb‐resistant PGPR in alleviating harmful effects of metal stress via activation of various defence mechanisms and enhancing Pb uptake that promotes tolerance of L. sativus to Pb stress.

     

Heavy metal (Pb) accumulation in metallophytes as influenced by the variations in rhizospheric and non-rhizospheric soils physico-chemical characteristics

Activities at root-soil interface determine the solubility and uptake of metals by plants. Metal accumulation in plant species (Imperata cylindrical, Cynodon dactylon, Eleucine indica, Gomphrena celosoides, Sporobolus pyramidalis, Chromolaena odorata and Rhynchospora corymbosa) growing on Pb contaminated site as influenced by variations in physico-chemical characteristics, dissolved organic matter (DOM), Pb fractionation and different functional groups (using Fourier Transmittance Infra-red) of rhizospheric and non-rhizospheric soils was assessed. The electrical conductivity (2660–5520 µs) and Pb concentrations (51390.0–64080.0 mg/kg) were more in non-rhizospheric than rhizospheric soils having 276 µs to 3160 µs EC and 3289.0 to 44850.0 mg/kg Pb. More nutrients, DOM and carbohydrates functional groups (C-O; 1100 -1000 and O-H; 3700–3600) were found in rhizospheric compared to non-rhizospheric soils. The pH was slightly acidic (5.0–5.54) and E. indica with the lowest pH (5.0) accumulated highest Pb concentrations in shoot (8030 mg/kg) and root (16380 mg/kg) while C. odorata with highest values of pH, P, Ca and Mg in rhizospheric soil accumulated the least (root; 331.6 and shoot: 209.0 mg/kg). Pb was more in organic and residual fractions of rhizospheric and non-rhizospheric soils respectively. Reduction in pH, EC coupled with nutrients and DOM availability increased Pb uptake by plants.     

重金属胁迫对毛竹种子萌发及其富集效应的影响

以毛竹种子为供试材料,研究4种重金属(Pb2+、Zn2+、Cu2+、Cd2+)胁迫对毛竹种子萌发的影响,并考察重金属在毛竹幼苗各组织部分的富集情况。结果表明:(1)Pb2+和Cd2+对毛竹种子的发芽率、发芽势、发芽指数及活力指数有抑制作用,低浓度下Cu2+和Zn2+对毛竹种子的发芽势、发芽率、发芽指数等指标有促进作用,高浓度则显著抑制;当浓度达到1600μmol/L时Cd2+对种子萌发的抑制效果明显强于其他3种元素;(2)选取根尖数、根表面积、根体积、根系总长4个根系形态指标发现,低浓度处理下Pb2+、Zn2+对根系生长有促进作用,而Cu2+和Cd2+起到明显的抑制作用;(3)处理10d后,种子萌发幼苗地上部对Pb2+、Zn2+、Cu2+、Cd2+的含量最高可达6810.51、1387.77、951.77、429.33 mg/kg,转移系数Zn2+Cd2+Pb2+Cu2+。综上,系统揭示了毛竹种子在重金属胁迫下的萌发和富集情况,为今后的土培、大田试验提供了有益的参考,也为将毛竹作为植物修复材料加以研究开启了新的研究视角,具有重要的研究价值。     

Salt tolerance and polyphyly in the cyanobacterium Chroococcidiopsis (Pleurocapsales)

Chroococcidiopsis Geitler (Geitler 1933) is a genus of cyanobacteria containing desiccation and radiation resistant strains. Members of the genus live in habitats ranging from hot and cold deserts to fresh and saltwater environments. Morphology and cell division pattern have historically been used to define the genus. To better understand the evolution and ability of the Chroococcidiopsis genus to survive in diverse environments we investigated how salt tolerance varies among 15 strains previously isolated from different locations, and if salt tolerant strains are monophyletic to those isolated from freshwater and land environments. Four markers were sequenced from these 15 strains, the 16S rRNA, rbcL, desC1, and gltX genes. Phylogenetic trees were generated which identified a distinct clade of salt‐tolerant strains. This study demonstrates that the genus is polyphyletic based on saltwater and freshwater phenotypes. To understand the resistance to salt in more details, the strains were grown on a range of sea salt concentrations which demonstrated that the freshwater strains were salt‐intolerant whilst the saltwater strains required salt for growth. This study shows an increased resolution of the phylogeny of Chroococcidiopsis and provides further evidence that the genus is polyphyletic and should be reclassified to improve clarity in the literature.     

Temperature × light interaction and tolerance of high water temperature in the planktonic freshwater flagellates Cryptomonas (Cryptophyceae) and Dinobryon (Chrysophyceae)

Using microcosm experiments, we investigated the interactive effects of temperature and light on specific growth rates of three species each of the phytoplanktonic genera Cryptomonas and Dinobryon. Several species of these genera play important roles in the food web of lakes and seem to be sensitive to high water temperature. We measured growth rates at three to four photon flux densities ranging from 10 to 240 μmol photon · m^?2 · s^?1 and at 4–5 temperatures ranging from 10°C to 28°C. The temperature × light interaction was generally strong, species specific, and also genus specific. Five of the six species studied tolerated 25°C when light availability was high; however, low light reduced tolerance of high temperatures. Growth rates of all six species were unaffected by temperature in the 10°C–15°C range at light levels ≤50 μmol photon · m^?2 · s^?1. At high light, growth rates of Cryptomonas spp. increased with temperature until the temperature optimum was reached and then declined. The Dinobryon species were less sensitive than Cryptomonas spp. to photon flux densities of 40 μmol photon · m^?2 · s^?1 and 200 μmol photon · m^?2 · s^?1 over the entire temperature range but did not grow under a combination of very low light (10 μmol photon · m^?2 · s^?1) and high temperature (≥20°C). Among the three Cryptomonas species, cell volume declined with temperature and the maximum temperature tolerated was negatively related to cell size. Since Cryptomonas is important food for microzooplankton, these trends may affect the pelagic carbon flow if lake warming continues.     

Genetic improvement of heavy metal tolerance in plants by transfer of the yeast metallothionein gene (CUP1)

Cauliflower (Brassica oleracea var. botrytis) tolerates treatment with 25 µM CdCl2 for eight days, but is killed by that with a 50 µM concentration. However, even 15 µM CdCl2 is toxic in the presence of 1 mM L-buthionine sulfoximine (BSO), suggesting the presence of a Cd-inducible phytochelatin and its involvement in Cd-tolerance in cauliflower. To develop heavy metal-tolerant transgenic plants, we ligated the structural gene of yeast metallothionein gene (CUP1) downstream of CaMV35S promoter and introduced the fused gene into cauliflower. A Cd-tolerant transgenic cauliflower was selected, which grew well in the presence of 400 µM or less Cd, whereas the non-transformed cauliflower tolerated only up to 25 µM Cd. The transgenic cauliflower accumulated more Cd, especially in the upper leaves, than the non-transformed plant.In conclusion, by transfer of the yeast metallothionein gene into cauliflower increased Cd-tolerance and Cd-accumulating ability can be conferred to the plant.     

Functional characterisation of two phytochelatin synthases in rice (Oryza sativa cv. Milyang 117) that respond to cadmium stress

• Cadmium (Cd) is one of the most toxic heavy metals and a non‐essential element to all organisms, including plants; however, the genes involved in Cd resistance in plants remain poorly characterised.
• To identify Cd resistance genes in rice, we screened a rice cDNA expression library treated with CdCl₂ using a yeast (Saccharomyces cerevisiae) mutant ycf1 strain (DTY167) and isolated two rice phytochelatin synthases (OsPCS5 and OsPCS15).
• The genes were strongly induced by Cd treatment and conferred increased resistance to Cd when expressed in the ycf1 mutant strain. In addition, the Cd concentration was twofold higher in yeast expressing OsPCS5 and OsPCS15 than in vector‐transformed yeast, and OsPCS5 and OsPCS15 localised in the cytoplasm. Arabidopsis thaliana plants overexpressing OsPCS5/‐15 paradoxically exhibited increased sensitivity to Cd, suggesting that overexpression of OsPCS5/‐15 resulted in toxicity due to excess phytochelatin production in A. thaliana.
• These data indicate that OsPCS5 and OsPCS15 are involved in Cd tolerance, which may be related to the relative abundances of phytochelatins synthesised by these phytochelatin synthases.

     

The role of the cell wall in the mechanism of lead and zinc tolerance in Anthoxanthum odoratum L

The respiration rate and viability of cultured cells and protoplasts isolated from two clones of Anthoxanthum odoratum tolerant to both zinc and lead were unaffected by the presence of zinc. Although intact cells were largely unaffected by the presence of lead, protoplasts isolated from cultured cells were susceptible, showing a reduced respiration rate and a high mortality. In contrast cultured cells and protoplasts of non-tolerant clones of A. odoratum were susceptible to both zinc and lead. The results provide direct evidence that in A. odoratum the cell wall is part of the mechanism of tolerance to lead, but not to zinc.     

Staphylococcus aureus giant protein Ebh is involved in tolerance to transient hyperosmotic pressure

Staphylococcus aureus is well known to colonize on human skin where the physiological condition is characterized by hypervariable water activity, i.e., repeated dehydration or rehydration. To determine the facilitating factors for the colonization under hypervariable water activity, we studied the giant protein Ebh (extracellular matrix (ECM)-binding protein homologue). The ebh mutant RAM8 showed invaginated vacuoles along the septum, similar to that found in partial plasmolysis, and the cells burst under osmotic upshift. RAM8 was also relatively susceptible to abrupt hyperosmotic upshift, teicoplanin, and Triton X-100. By using the green fluorescent protein (GFP) as a reporter, Ebh was localized over the entire cell surface. This suggests that Ebh might contribute to structural homeostasis by forming a bridge between the cell-wall and cytoplasmic membrane to avoid plasmolysis under hyperosmotic condition.