Plant–plant interactions and local patterns of diversity from semi-arid to subalpine Mediterranean plant communities

An understanding of the diversity spatial organization in plant communities provides essential information for management and conservation planning. In this study we investigated, using a multi-species approach, how plant–plant interactions determine the local structure and composition of diversity in a set of Mediterranean plant communities, ranging from semi-arid to subalpine habitats. Specifically, we evaluated the spatial pattern of diversity (i.e., diversity aggregation or segregation) in the local neighborhood of perennial plant species using the ISAR (individual species–area relationship) method. We also assessed the local pattern of beta-diversity (i.e., the spatial heterogeneity in species composition among local assemblages), including the contribution of species turnover (i.e., species replacement) and nestedness (i.e., differences in species richness) to the overall local beta-diversity. Our results showed that local diversity segregation decreased in the less productive plant communities. Also, we found that graminoids largely acted as diversity segregators, while forbs showed more diverse neighborhoods than expected in less productive study sites. Interestingly, not all shrub and dwarf shrub species aggregated diversity in their surroundings. Finally, an increase in nestedness was associated with less segregated diversity patterns in the local neighborhood of shrub species, underlining their role in creating diversity islands in less productive environmental conditions. Our results provide further insights into the effect of plant–plant interactions in shaping the structure and composition of diversity in Mediterranean plant communities, and highlight the species and groups of species that management and conservation strategies should focus on in order to prevent a loss of biodiversity.

     

Comparing the conservatism of ecological interactions in plant–pollinator and plant–herbivore networks

Conservatism in species interaction, meaning that related species tend to interact with similar partners, is an important feature of ecological interactions. Studies at community scale highlight variations in conservatism strength depending on the characteristics of the ecological interaction studied. However, the heterogeneity of datasets and methods used prevent to compare results between mutualistic and antagonistic networks. Here we perform such a comparison by taking plant–insect communities as a study case, with data on plant–herbivore and plant–pollinator networks. Our analysis reveals that plants acting as resources for herbivores exhibit the strongest conservatism in species interaction among the four interacting groups. Conservatism levels are similar for insect pollinators, insect herbivores and plants as interacting partners of pollinators, although insect pollinators tend to have a slightly higher conservatism than the two others. Our results thus clearly support the current view that within antagonistic networks, conservatism is stronger for species as resources than for species as consumer. Although the pattern tends to be opposite for plant–pollinator networks, our results suggest that asymmetry in conservatism is much less pronounced between the pollinators and the plant they interact with. We discuss these differences in conservatism strength in relation with the processes structuring plant–insect communities.     

Genotype–environment interactions affect flower and fruit herbivory and plant chemistry of Arabidopsis thaliana in a transplant experiment

Large differences exist in flower and fruit herbivory between dune and inland populations of plants of Arabidopsis thaliana (Brassicaceae). Two specialist weevils Ceutorhynchus atomus and C. contractus (Curculionidae) and their larvae are responsible for this pattern in herbivory. We test, by means of a reciprocal transplant experiment, whether these differences reflect environmental influences or genetic variation in plant defense level. All plants suffered more damage after being transplanted to the dune site than after being transplanted to the inland site. Plants of inland origin suffered more flower and fruit herbivory than plants of dune origin when grown at the dune transplant site, but differences were much smaller at the inland site. Both flower damage by adult weevils and fruit damage by their larvae were subject to significant genotype × environment interactions. The observed pattern in herbivory is a strong indication for local adaption of plant defense to the level of herbivory by Ceutorhynchus. In order to identify the mechanism of defense, a quantitative analysis of glucosinolates was performed on the seeds with HPLC. Highly significant differences were found in glucosinolate types and total concentration. These patterns were mainly determined by the origin of the plants (dune or inland) and by a genotype × environment interaction. Herbivory was not significantly correlated to the concentration of glucosinolates in seeds. We therefore analyzed the total metabolic composition of seeds, using NMR spectroscopy and multivariate data analysis. Major differences in chemical composition were found in the water–methanol fractions: more glucosinolate and sucrose in the dune and more fatty acids, lipids and sinapoylmalate in the inland populations. We discuss which of these chemical factors could explain the marked differences in damage between populations.     

Using functional–structural plant models to study, understand and integrate plant development and ecophysiology

Functional–structural plant models (FSPMs) explore and integrate relationships between a plant’s structure and processes that underlie its growth and development. In recent years, the range of topics being addressed by scientists interested in functional–structural plant modelling has expanded greatly. FSPM techniques are now being used to dynamically simulate growth and development occurring at the microscopic scale involving cell division in plant meristems to the macroscopic scales of whole plants and plant communities. The plant types studied also cover a broad spectrum from algae to trees. FSPM is highly interdisciplinary and involves scientists with backgrounds in plant physiology, plant anatomy, plant morphology, mathematics, computer science, cellular biology, ecology and agronomy. This special issue of Annals of Botany features selected papers that provide examples of comprehensive functional–structural models, models of key processes such as partitioning of resources, software for modelling plants and plant environments, data acquisition and processing techniques and applications of functional–structural plant models for agronomic purposes.     

Additive effects of exotic plant abundance and land-use intensity on plant–pollinator interactions

The continuing spread of exotic plants and increasing human land-use are two major drivers of global change threatening ecosystems, species and their interactions. Separate effects of these two drivers on plant–pollinator interactions have been thoroughly studied, but we still lack an understanding of combined and potential interactive effects. In a subtropical South African landscape, we studied 17 plant–pollinator networks along two gradients of relative abundance of exotics and land-use intensity. In general, pollinator visitation rates were lower on exotic plants than on native ones. Surprisingly, while visitation rates on native plants increased with relative abundance of exotics and land-use intensity, pollinator visitation on exotic plants decreased along the same gradients. There was a decrease in the specialization of plants on pollinators and vice versa with both drivers, regardless of plant origin. Decreases in pollinator specialization thereby seemed to be mediated by a species turnover towards habitat generalists. However, contrary to expectations, we detected no interactive effects between the two drivers. Our results suggest that exotic plants and land-use promote generalist plants and pollinators, while negatively affecting specialized plant–pollinator interactions. Weak integration and high specialization of exotic plants may have prevented interactive effects between exotic plants and land-use. Still, the additive effects of exotic plants and land-use on specialized plant–pollinator interactions would have been overlooked in a single-factor study. We therefore highlight the need to consider multiple drivers of global change in ecological research and conservation management.     

Recent applications of biotechnological approaches to elucidate the biology of plant–nematode interactions

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Plant–microbiome interactions and their impacts on plant adaptation to climate change

Plants have co-evolved with a wide range of microbial communities over hundreds of millions of years, this has drastically influenced their adaptation to biotic and abiotic stress. The rapid development of multi-omics approaches has greatly improved our understanding of the diversity, composition, and functions of plant microbiomes, but how global climate change affects the assembly of plant microbiomes and their roles in regulating host plant adaptation to changing environmental conditions is not fully known. In this review, we summarize recent advancements in the community assembly of plant microbiomes, and their responses to climate change factors such as elevated CO₂ levels, warming, and drought. We further delineate the research trends and hotspots in plant–microbiome interactions in the context of climate change, and summarize the key mechanisms by which plant microbiomes influence plant adaptation to the changing climate. We propose that future research is urgently needed to unravel the impact of key plant genes and signal molecules modulated by climate change on microbial communities, to elucidate the evolutionary response of plant–microbe interactions at the community level, and to engineer synthetic microbial communities to mitigate the effects of climate change on plant fitness.     

植物苯丙烷代谢及其对重金属胁迫的响应研究进展

苯丙烷代谢途径是植物中最重要的次生代谢途径之一,在植物抵抗重金属胁迫中直接或间接发挥了抗氧化作用,并能够提高植物对重金属离子的吸收与胁迫耐性。本文就苯丙烷代谢途径核心反应与关键酶系进行了总结,同时分析了木质素、类黄酮及原花青素等关键代谢产物的生物合成过程及相关机制,并以此为基础探讨了苯丙烷代谢途径关键产物响应重金属胁迫的相关机制。此外,结合当前研究现状,就苯丙烷代谢参与植物防御重金属胁迫的相关研究提出展望,以期为重金属污染环境的植物修复提供理论依据。     

Study of stationary phase metabolism via isotopomer analysis of amino acids from an isolated protein

Microbial production of many commercially important secondary metabolites occurs during stationary phase, and methods to measure metabolic flux during this growth phase would be valuable. Metabolic flux analysis is often based on isotopomer information from proteinogenic amino acids. As such, flux analysis primarily reflects the metabolism pertinent to the growth phase during which most proteins are synthesized. To investigate central metabolism and amino acids synthesis activity during stationary phase, addition of fully ¹³C‐labeled glucose followed by induction of green fluorescent protein (GFP) expression during stationary phase was used. Our results indicate that Escherichia coli was able to produce new proteins (i.e., GFP) in the stationary phase, and the amino acids in GFP were mostly from degraded proteins synthesized during the exponential growth phase. Among amino acid biosynthetic pathways, only those for serine, alanine, glutamate/glutamine, and aspartate/asparagine had significant activity during the stationary phase. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2010     

cDNA cloning and heterologous expression of coniferin β-glucosidase

Coniferin -glucosidase (CBG) catalyzes the hydrolysis of monolignol glucosides to release the cinnamyl alcohols for oxidative polymerization to lignin. Utilizing the N-terminal amino acid sequence of the purified enzyme, the corresponding full-length cDNA sequence was isolated from a Pinus contorta xylem-specific library. The isolated 1909 nucleotide cDNA was confirmed to be that of CBG on the basis of its high homology to family 1 glycosyl hydrolases, the sequence identity with the N-terminal amino acid residues of the purified enzyme, and the coniferin hydrolytic activity and substrate specificity profile displayed by the recombinant protein when expressed in Escherichia coli. The presence of a 23 amino acid N-terminal signal peptide in the deduced 513 amino acid enzyme suggests that CBG is a secretory protein targeted to the ER. The isolation of CBG cDNA will facilitate the evaluation of the importance of this enzyme in the ultimate stages of lignin biosynthesis and could be a valuable tool in manipulating lignin levels in xylem cell walls.     

Regulation of phenylpropanoid metabolism by exogenous precursors in axenic cultures of Sphagnum fallax

Sphagnum plantlets, cultivated in continuous-feed bioreactors, are characterised by high levels of free endogenous phenolics and a pronounced excretion of some phenolics into the effluent culture medium. The transfer of Sphagnum fallax, precultivated in continuous-feed bioreactors, to batch cultures resulted in an increased flux through phenylpropanoid metabolism and an accumulation of p-coumaric acid to 0.1 μM and of trans-sphagnum acid up to 0.5 μM in the external medium [³H]-labelled L-phenylalanine (7.7 GBq mol^?1) was rapidly taken up, resulting in an enhanced synthesis and excretion of p-coumaric and trans-sphagnum acid. Specific activities were 6.9 and 5.4 GBq mol^?1, respectively, for these cinnamic acids excreted into the external medium. Endogenous pools of trans-cinnamic and p-coumaric acid did not increase and no labelling could be detected in these compounds. Cell wall-bound activity amounted to ca 14% of the applied activity after 48 h of incubation, 59% of which was recovered in dioxane/2 M HCl extracts of the cell wall. Exogenously applied trans-cinnamic acid (0.1 mM) was taken up to 46% and resulted in a transient endogenous accumulation of trans-cinnamic acid, the level of free endogenous p-coumaric and trans-sphagnum acid was found to have decreased. The concentrations of p-coumaric and trans-sphagnum acid in the culture medium rose to 17 and 2.4 μM, respectively, after 48 h of incubation in 0.1 mMtrans-cinnamic acid. Exogenously applied p-coumaric acid (0.1 mM) was taken up to 79% from the incubation solution but not stored endogenously, as metabolic products trans-sphagnum acid and an unknown p-coumaric acid-conjugate accumulated in the external medium and endogenously. These results give evidence for the biosynthetical route from phenylalanine to sphagnum acid and a channelling of pathway intermediates by the enzymes L-phenylalanine ammonia-lyase (EC 4.3.1.5) and cinnamic acid 4-hydroxylase (EC 1.14.13.11).     

Chemical Studies on Heated Starch/Glycine Model Systems

Sixty-three compounds were isolated and identified from heated starch and from heated starch with glycine. Starch or starch with glycine was heated in an Erlenmeyer flask at 290°C under a nitrogen stream. The volatiles formed during heating were entrained on a porous polymer (Porapack Q). Residual charred materials in the flasks were extracted with methylene chloride. The oily dark brown materials recovered from both the Porapack Q traps and the methylene chloride extracts were subjected to gas chromatography and gas chromatography/mass spectrometry. The compounds identified include 3 hydrocarbons, 11 ketones, 3 aldehydes, 24 aromatic compounds, 10 furans and 12 nitrogen-containing compounds. Formation mechanisms of some major products are proposed.     

苯丙烷代谢基因差异表达对宁夏枸杞适应盐胁迫的调控作用

为探究盐胁迫条件下宁夏枸杞苯丙烷代谢相关基因差异表达规律,以不同浓度NaCl(0,100,200,300 mmol/L)处理的水培宁夏枸杞幼苗为研究材料,利用高通量测序技术和qRT-PCR对盐胁迫下宁夏枸杞苯丙烷代谢相关基因差异表达进行分析,同时对该途径中关键酶活性及产物含量进行测定。结果表明,(1)宁夏枸杞在不同浓度NaCl处理下共有58个苯丙烷代谢相关基因差异表达,且随着盐胁迫程度的增加大部分基因表达水平上调或不变;(2)随着NaCl浓度的增加,宁夏枸杞叶片抗氧化酶SOD、POD、CAT的活性均下降,而酚类物质、类黄酮和木质素的含量在100 mmol/L NaCl处理下均显著积累。研究发现,宁夏枸杞可能通过调控苯丙烷代谢相关基因上调表达,增加酚类物质、类黄酮和木质素的合成,来清除过多活性氧和提升细胞壁强度以适应盐胁迫;宁夏枸杞可耐受的NaCl浓度在100~200 mmol/L之间。     

莫西霉素高产菌株的构建

【背景】 莫西霉素(kirromycin)是由山丘链霉菌(Streptomyces collinus) Tü 365产生的一种复杂线性聚酮-非核糖体肽类化合物,可与细菌延伸因子EF-Tu相互作用,阻碍蛋白质合成,具有窄谱抑菌活性。目前莫西霉素作为实验试剂用于核糖体结构和功能研究。近年来有研究报道,莫西霉素及其类似物抗沃尔巴克氏体(Wolbachia)活性优于注册药物多西环素,有望成为治疗丝状线虫感染的新先导化合物。【目的】 运用组合代谢工程方法,构建莫西霉素高产菌株,实现莫西霉素产量的提升。【方法】 基于莫西霉素生物合成基因簇以及生物合成途径分析,利用组成型启动子kasOp^*过表达或组合过表达莫西霉素生物合成基因簇内的巴豆酰辅酶A还原酶编码基因kirN、天冬氨酸- 1-脱羧酶编码基因kirD、磷酸泛酰巯基乙胺转移酶编码基因kirP、转运蛋白超家族外排泵编码基因kirTI和kirTII、天蓝色链霉菌(Streptomyces coelicolor) A3(2)中乙酰辅酶A羧化酶编码基因acc等,实现莫西霉素产量的提升。【结果】 过表达/组合过表达上述基因对莫西霉素产量均有一定提升效果,其中,单独过表达acc及组合过表达kirD、kirN、kirP、kirTI和kirTII的效果更好,莫西霉素产量较野生型菌株分别提高了57.8%和65.6%,达到198.3 mg/L和208.1 mg/L。此外,通过在公开的细菌基因组数据库中搜索莫西霉素生物合成酶的同源蛋白编码基因,发现31个预测可以合成莫西霉素类天然产物的生物合成基因簇。【结论】 本研究运用代谢工程方法有效提升了莫西霉素的产量,为进一步推动莫西霉素的应用开发奠定了基础。