Pectic polysaccharides are attacked by hydroxyl radicals in ripening fruit: evidence from a fluorescent fingerprinting method

Background and aims Many fruits soften during ripening, which is important commercially and in rendering the fruit attractive to seed-dispersing animals. Cell-wall polysaccharide hydrolases may contribute to softening, but sometimes appear to be absent. An alternative hypothesis is that hydroxyl radicals (^•OH) non-enzymically cleave wall polysaccharides. We evaluated this hypothesis by using a new fluorescent labelling procedure to ‘fingerprint’ ^•OH-attacked polysaccharides.Methods We tagged fruit polysaccharides with 2-(isopropylamino)-acridone (pAMAC) groups to detect (a) any mid-chain glycosulose residues formed in vivo during ^•OH action and (b) the conventional reducing termini. The pAMAC-labelled pectins were digested with Driselase, and the products resolved by high-voltage electrophoresis and high-pressure liquid chromatography.Key Results Strawberry, pear, mango, banana, apple, avocado, Arbutus unedo, plum and nectarine pectins all yielded several pAMAC-labelled products. GalA–pAMAC (monomeric galacturonate, labelled with pAMAC at carbon-1) was produced in all species, usually increasing during fruit softening. The six true fruits also gave pAMAC·UA-GalA disaccharides (where pAMAC·UA is an unspecified uronate, labelled at a position other than carbon-1), with yields increasing during softening. Among false fruits, apple and strawberry gave little pAMAC·UA-GalA; pear produced it transiently.Conclusions GalA–pAMAC arises from pectic reducing termini, formed by any of three proposed chain-cleaving agents (^•OH, endopolygalacturonase and pectate lyase), any of which could cause its ripening-related increase. In contrast, pAMAC·UA-GalA conjugates are diagnostic of mid-chain oxidation of pectins by ^•OH. The evidence shows that ^•OH radicals do indeed attack fruit cell wall polysaccharides non-enzymically during softening in vivo. This applies much more prominently to drupes and berries (true fruits) than to false fruits (swollen receptacles). ^•OH radical attack on polysaccharides is thus predominantly a feature of ovary-wall tissue.     

Solution NMR characterization of apical membrane antigen 1 and small molecule interactions as a basis for designing new antimalarials

Plasmodium falciparum apical membrane antigen 1 (PfAMA1) plays an important role in the invasion by merozoites of human red blood cells during a malaria infection. A key region of PfAMA1 is a conserved hydrophobic cleft formed by 12 hydrophobic residues. As anti‐apical membrane antigen 1 antibodies and other inhibitory molecules that target this hydrophobic cleft are able to block the invasion process, PfAMA1 is an attractive target for the development of strain‐transcending antimalarial agents. As solution nuclear magnetic resonance spectroscopy is a valuable technique for the rapid characterization of protein–ligand interactions, we have determined the sequence‐specific backbone assignments for PfAMA1 from two P. falciparum strains, FVO and 3D7. Both selective labelling and unlabelling strategies were used to complement triple‐resonance experiments in order to facilitate the assignment process. We have then used these assignments for mapping the binding sites for small molecules, including benzimidazoles, pyrazoles and 2‐aminothiazoles, which were selected on the basis of their affinities measured from surface plasmon resonance binding experiments. Among the compounds tested, benzimidazoles showed binding to a similar region on both FVO and 3D7 PfAMA1, suggesting that these compounds are promising scaffolds for the development of novel PfAMA1 inhibitors. Copyright © 2016 John Wiley & Sons, Ltd.     

Growing rice in controlled environments

Rice (Oryza sativa) is less frequently used in basic research than Arabidopsis, although rice is a valuable model system for many monocot crops and possesses a high genetic variability in physiologically as well as agriculturally relevant features such as abiotic stress tolerance, nutrient efficiency and flower time control. A reason is the seemingly difficult cultivation of rice outside the rice production area. This review aims to assist newcomers to the field to develop cultivation protocols for their local controlled environment. The main challenges are high light demands, photoperiodicity and low micronutrient efficiency. The nutrient efficiency problem can be overcome by adding micronutrient fertiliser to potting substrates and keeping the soil waterlogged to increase micronutrient availability and mobility. Cultivation of rice on adjusted hydroponic solutions with high iron concentration provides the basis for successful heavy isotope labelling. Many rice cultivars need high light intensities in combination with short‐day conditions to complete their life cycle. However, some photoperiod‐insensitive cultivars will flower even under relatively low light intensities. In highly photoperiod‐sensitive cultivars, like Nipponbare, flowering can be induced by a limited period of short‐day treatment in the sensitive period, after which the cultivation can be continued in long‐day conditions. The life cycle of many cultivars is completed in 90 to 120 days, its length being thus comparable to Arabidopsis and shorter than in other cereals. In conclusion, with the right cultivation technique, rice is an amiable model species for researchers beyond the rice area too.     

Chirality and biosynthesis of lilac compounds in Actinidia arguta flowers

Biosynthesis of lilac compounds in ‘Hortgem Tahi’ kiwifruit (Actinidia arguta) flowers was investigated by treating inflorescences with d₅-linalool. The incorporation of the deuterium label into 8-hydroxylinalool, 8-oxolinalool, the lilac aldehydes, alcohols, and alcohol epoxides was followed by GC-MS and enantioselective GC-MS. Both (R)- and (S)-linalool were produced naturally by the flowers, but 8-hydroxylinalool, 8-oxolinalool, and the lilac aldehydes and alcohols occurred predominantly as the (S) and 5′(S)-diastereoisomers, respectively. The enantioselective step in the biosynthesis of the lilac aldehydes and alcohols was concluded to be the oxidation of linalool to (S)-8-hydroxylinalool. In contrast, the lilac alcohol epoxides had a 5′(R):(S) ratio, the same as for linalool, which suggests that either these compounds are not synthesised from the 5′(S)-configured lilac aldehydes and alcohols, or that if indeed they are, then it is by an enantioselective step that favours utilisation of the 5′(R)-configured compounds.     

Investigation of the genetic diversity of Phytophthora capsici in China using a universal fluorescent labelling method

Phytophthora capsici is an important oomycete pathogen threatening the vegetable production in China, but very little is known about its population structure. The objective of the present study was to evaluate the genetic diversity of 49 P. capsici isolates obtained from 2007 to 2014 at nine provincial locations in China. Isolates were assessed for mating type, metalaxyl resistance and simple sequence repeat (SSR) genotype. Mating‐type analyses of the isolates showed that both mating types were present in all of the sampled production regions, and the mating‐type frequency in the total Chinese population did not deviate significantly from a 1:1 ratio. Responses of isolates to the fungicide metalaxyl indicated the presence of intermediate resistance to metalaxyl among the field population. A universal fluorescent labelling method was adapted in this study to improve the efficiency of SSR genotyping. Microsatellite genotyping of the isolates using seven SSR markers revealed 44 unique multilocus genotypes. Genetic analyses indicated the existence of two genetic clusters within Chinese P. capsici collection. Clonal reproduction may play a more prominent role in Yunnan Province, but non‐existence of repeated genotypes and existence of both mating types throughout all regions suggest outcrossing and sexual recombination likely play an important role in the overall epidemiology in China. Future studies would include expanded scale sampling at single regions over multiple years to better define the genetic diversity of P. capsici in China.     

O-GlcNAcylation promotes fatty acid synthase activity under nutritional stress as a pro-survival mechanism in cancer cells

Protein O-GlcNAcylation is a specific form of protein glycosylation that targets a wide range of proteins with important functions. O-GlcNAcylation is known to be deregulated in cancer and has been linked to multiple aspects of cancer pathology. Despite its ubiquity and importance, the current understanding of the role of O-GlcNAcylation in the stress response remains limited. In this study, we performed a quantitative chemical proteomics-based open study of the O-GlcNAcome in HeLa cells, and identified 163 differentially-glycosylated proteins under starvation, involving multiple metabolic pathways. Among them, fatty acid metabolism was found to be targeted and subsequent analysis confirmed that fatty acid synthase (FASN) is O-GlcNAcylated. O-GlcNAcylation led to enhanced de novo fatty acid synthesis (FAS) activity, and fatty acids contributed to the cytoprotective effects of O-GlcNAcylation under starvation. Moreover, dual inhibition of O-GlcNAcylation and FASN displayed a strong synergistic effect in vitro in inducing cell death in cancer cells. Together, the results from this study provide novel insights into the role of O-GlcNAcylation in the nutritional stress response and suggest the potential of combining inhibition of O-GlcNAcylation and FAS in cancer therapy.     

Tn5Map, a transposon for the rapid mapping of restriction sites in plasmids

Abstract A transposon was constructed allowing the rapid restriction mapping of plasmids. This transporon, Tn5Map, contains a cleavage site for the I- Sce I endonuclease which recognizes an 18-mer. After iivo transposition of Tn5Map into the plasmid of interest, the plasmid is isolated and linearized with I- Sce I. Splinkers labelled with digoxygenin and complementary to the left and right end of the linearized molecule are added and ligated. After partial digestion of the splinkered molecules with the restriction enzyme of interest, separation of the cleavage products in an agarose gel, and Southern transfer, the labelled fragments are visualized by the addition of the chemiluminescent substrate AMPPD and alkaline phosphatase. The restriction map can be directly read from the bottom to the top of the gel.     

玉米两个RFLP标记的原位单杂交与共杂交定位的比较

ＲＦＬＰ标记ｂｎ１８．２３和 ｕｍｃ１１１位于玉米遗传日第 ４连锁群近端,彼此密切连锁但次序尚未确定。用生物素标记对它们进行了原位单杂交和共杂交的比较定位。在植物中,这类原位共杂交的研究为首次报道。在单一探针的原位杂交中 ｕｍｃ１１１被定位在第 １、 ４和９染色体长上,与着丝粒的百分距离分别是７．３６±２．６５、６３．６７±１．０７、４７．８７±２．９０。ｂｎ１８．２３被定位在第４和８染色体长臂上,与着丝粒的百分距离分别是８７．４２±２．４５和２７．６０±１．７５,清楚地表明了这两个标记在第４染色体上的次序。ｂｎ１８．２３和ｕｍｃ１１１分别与编码过氧化氢酶的ｃａｔ３基因和编码丝氨酸／苏氨酸蛋白激酶的ｃｄｅ２Ａ基因紧密连锁。根据供试ＲＦＬＰ标记检出位点推断了基因ｃｄｃ２Ａ和ｃａｔ３的物理位置。原位共杂交在第 ４染色体长臂上同时显示出了ｕｍｃ１１１和ｂｎ１８．２３两个标记的杂交信号,它们的位置分别与单一探针原位杂交的位置基本吻合。这为低拷贝或单一拷贝等小片段ＤＮＡ物理定位的可靠性以及它们共杂交的可行性提供了令人信服的证据。