A large English population of the temperate tuberous Greater Butterfly-orchid,
Platanthera chlorantha
, was monitored through a 16-year period. Each June the number of flowering plants was counted ...and 60 flowering plants were measured
in situ
for four morphological traits, selected for both ease of measurement and their contrasting contributions to the life history of the species. Trait data were tested annually in pairwise combinations for individual plants, before mean values throughout the study period were regressed and cross-correlated against each other and against local data for four meteorological parameters. Labellar spur length proved to be more constrained than either flower number or stem height, and rarely yielded statistically significant correlations with other traits, whereas the three remaining traits reliably showed modest but significant correlations. Mean values and coefficients of variation differed only modestly among years and showed few of any meaningful trends. Spring rainfall and insolation had no detectable effect on traits of plants flowering that June; instead, they impacted on trait expression during the following year, presumably as a result of differential resourcing of replacement tubers formed during the previous year. High spring rainfall in year t–1 increased leaf area and stem height in year t, whereas the widely fluctuating number of flowering plants was highest in years immediately following those characterised by relatively dry and/or sunny springs. The “decision” to flower is taken during the previous summer, though it may be modified through winter/spring abortion of above-ground organs. The proportion of the population electing to flower is the only measured parameter that impacts significantly on annual reproductive output, emphasising the under-rated difficulty of evolving through directional selection. Any attempt to predict the behaviour of plant species in response to climate change must integrate information on demography with that on life history, habitat preference and intimate symbioses.
Histone H1 and HMGB1 (high-mobility group protein B1) are the most abundant chromosomal proteins apart from the core histones (on average, one copy per nucleosome and per ten nucleosomes ...respectively). They are both highly mobile in the cell nucleus, with high on/off rates for binding. In vivo and in vitro evidence shows that both are able to organize chromatin structure, with H1 binding resulting in a more stable structure and HMGB1 binding in a less stable structure. The binding sites for H1 and HMGB1 in chromatin are partially overlapping, and replacement of H1 by HMGB1 through the highly dynamic nature of their binding, possibly facilitated by interaction between them, could result in switching of chromatin states. Binding of HMGB1 to DNA or chromatin is regulated by its long and highly acidic tail, which is also involved in H1 binding. The present article focuses mainly on HMGB1 and its interaction with chromatin and H1, as well as its chaperone role in the binding of certain transcription factors (e.g. p53) to their cognate DNA.
Hemicellulose polysaccharides influence assembly and properties of the plant primary cell wall (PCW), perhaps by interacting with cellulose to affect the deposition and bundling of cellulose fibrils. ...However, the functional differences between plant cell wall hemicelluloses such as glucomannan, xylan, and xyloglucan (XyG) remain unclear. As the most abundant hemicellulose, XyG is considered important in eudicot PCWs, but plants devoid of XyG show relatively mild phenotypes. We report here that a patterned β-galactoglucomannan (β-GGM) is widespread in eudicot PCWs and shows remarkable similarities to XyG. The sugar linkages forming the backbone and side chains of β-GGM are analogous to those that make up XyG, and moreover, these linkages are formed by glycosyltransferases from the same CAZy families. Solid-state nuclear magnetic resonance indicated that β-GGM shows low mobility in the cell wall, consistent with interaction with cellulose. Although Arabidopsis β-GGM synthesis mutants show no obvious growth defects, genetic crosses between β-GGM and XyG mutants produce exacerbated phenotypes compared with XyG mutants. These findings demonstrate a related role of these two similar but distinct classes of hemicelluloses in PCWs. This work opens avenues to study the roles of β-GGM and XyG in PCWs.
The major nutrients available to human colonic Bacteroides species are glycans, exemplified by pectins, a network of covalently linked plant cell wall polysaccharides containing galacturonic acid ...(GalA). Metabolism of complex carbohydrates by the Bacteroides genus is orchestrated by polysaccharide utilization loci (PULs). In Bacteroides thetaiotaomicron, a human colonic bacterium, the PULs activated by different pectin domains have been identified; however, the mechanism by which these loci contribute to the degradation of these GalA-containing polysaccharides is poorly understood. Here we show that each PUL orchestrates the metabolism of specific pectin molecules, recruiting enzymes from two previously unknown glycoside hydrolase families. The apparatus that depolymerizes the backbone of rhamnogalacturonan-I is particularly complex. This system contains several glycoside hydrolases that trim the remnants of other pectin domains attached to rhamnogalacturonan-I, and nine enzymes that contribute to the degradation of the backbone that makes up a rhamnose-GalA repeating unit. The catalytic properties of the pectin-degrading enzymes are optimized to protect the glycan cues that activate the specific PULs ensuring a continuous supply of inducing molecules throughout growth. The contribution of Bacteroides spp. to metabolism of the pectic network is illustrated by cross-feeding between organisms.
Xylan, a hemicellulosic component of the plant cell wall, is one of the most abundant polysaccharides in nature. In contrast to dicots, xylan in grasses is extensively modified by α-(1,2)– and ...α-(1,3)–linked arabinofuranose. Despite the importance of grass arabinoxylan in human and animal nutrition and for bioenergy, the enzymes adding the arabinosyl substitutions are unknown. Here we demonstrate that knocking-down glycosyltransferase (GT) 61 expression in wheat endosperm strongly decreases α-(1,3)–linked arabinosyl substitution of xylan. Moreover, heterologous expression of wheat and rice GT61s in Arabidopsis leads to arabinosylation of the xylan, and therefore provides gain-of-function evidence for α-(1,3)-arabinosyltransferase activity. Thus, GT61 proteins play a key role in arabinoxylan biosynthesis and therefore in the evolutionary divergence of grass cell walls.
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BFBNIB, NMLJ, NUK, PNG, SAZU, UL, UM, UPUK
The most abundant member of the collagen protein family, collagen I (also known as type I collagen; COL1), is composed of one unique (chain B) and two similar (chain A) polypeptides that ...self-assemble with one amino acid offset into a heterotrimeric triple helix. Given the offset, chain B can occupy either the leading (BAA), middle (ABA) or trailing (AAB) position of the triple helix, yielding three isomeric biomacromolecules with different protein recognition properties. Despite five decades of intensive research, there is no consensus on the position of chain B in COL1. Here, three triple-helical heterotrimers that each contain a putative von Willebrand factor (VWF) and discoidin domain receptor (DDR) recognition sequence from COL1 were designed with chain B permutated in all three positions. AAB demonstrated a strong preference for both VWF and DDR, and also induced higher levels of cellular DDR phosphorylation. Thus, we resolve this long-standing mystery and show that COL1 adopts an AAB register.
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FZAB, GEOZS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Facilitated binding of p53 to DNA by high mobility group B1 (HMGB1) may involve interaction between the N-terminal region of p53 and the high mobility group (HMG) boxes, as well as HMG-induced ...bending of the DNA. Intramolecular shielding of the boxes by the HMGB1 acidic tail results in an unstable complex with p53 until the tail is truncated to half its length, at which point the A box, proposed to be the preferred binding site for p53(1–93), is exposed, leaving the B box to bind and bend DNA. The A box interacts with residues 38–61 (TAD2) of the p53 transactivation domain. Residues 19–26 (TAD1) bind weakly, but only in the context of p53(1–93) and not as a free TAD1 peptide. We have solved the structure of the A-box/p53(1–93) complex by nuclear magnetic resonance spectroscopy. The incipient amphipathic helix in TAD2 recognizes the concave DNA-binding face of the A box and may be acting as a single-stranded DNA mimic.
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► Binding of p53 to its cognate DNA is facilitated by HMGB1 ► The N-terminal region of p53 (residues 38–61; TAD2) interacts with the HMG boxes ► The acidic tail of HMGB1 masks the p53 binding site in the free proteins ► The structure of the A-box/p53(1–93) complex shows that TAD2 acts as an ss-DNA mimic
HMGB1 facilitates binding of p53 to its cognate, DNA, through interaction between the N-terminal region of p53 (p53N) and the HMG boxes. Rowell et al. report a structure of the complex between HMGB1 A-box and p53N, showing that p53N recognizes the DNA-binding face of the A box, potentially acting as an ssDNA mimic.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Plant type II arabinogalactan (AG) polysaccharides are attached to arabinogalactan proteins (AGPs) at hydroxyproline residues, and they are very diverse and heterogeneous structures. The AG consists ...of a β-(1 → 3)-linked galactan backbone with β-(1 → 6)-galactan side chains that are modified mainly with arabinose, but they may also contain glucuronic acid, rhamnose or other sugars. Here, we studied the positions of fucose substitutions in AGPs, and we investigated the functions of this fucosylation. Monosaccharide analysis of Arabidopsis leaf AGP extracts revealed a significant reduction in L-Fucose content in the fut4 mutant, but not in the fut6 mutant. In addition, Fucose was reduced in the fut4 mutant in root AGP extracts and was absent in the fut4/fut6 mutant. Curiously, in all cases reduction of fucose was accompanied with a reduction in xylose levels. The fucosylated AGP structures in leaves and roots in wild type and fut mutant plants were characterised by sequential digestion with AG specific enzymes, analysis by Polysaccharide Analysis using Carbohydrate gel Electrophoresis, and Matrix Assisted Laser Desorption/Ionisation (MALDI)-Time of Flight Mass spectrometry (MS). We found that FUT4 is solely responsible for the fucosylation of AGPs in leaves. The Arabidopsis thaliana FUT4 and FUT6 genes have been previously proposed to be non-redundant AG-specific fucosyltransferases. Unexpectedly, FUT4 and FUT6 enzymes both fucosylate the same AGP structures in roots, suggesting partial redundancy to each other. Detailed structural characterisation of root AGPs with high energy MALDI-Collision Induced Dissociation MS and NMR revealed an abundant unique AG oligosaccharide structure consisting of terminal xylose attached to fucose. The loss of this structure in fut4/fut6 mutants explains the reduction of both fucose and xylose in AGP extracts. Under salt-stress growth conditions the fut4/fut6 mutant lacking AGP fucosylation exhibited a shorter root phenotype than wild type plants, implicating fucosylation of AGPs in maintaining proper cell expansion under these conditions.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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