(1→3)-β-D-Glucan (callose) is a probable intermediate in biosynthesis of cellulose of cotton fibres

Genome sequence of Gossypium anomalum facilitates interspecific introgression breeding

Crop wild relatives are an important reservoir of natural biodiversity. However, incorporating wild genetic diversity into breeding programs is often hampered by reproductive barriers and a lack of accurate genomic information. We assembled a high-quality, accurately centromere-anchored genome of Gossypium anomalum, a stress-tolerant wild cotton species. We provided a strategy to discover and transfer agronomically valuable genes from wild diploid species to tetraploid cotton cultivars. With a (Gossypium hirsutum × G. anomalum)2 hexaploid as a bridge parent, we developed a set of 74 diploid chromosome segment substitution lines (CSSLs) of the wild cotton species G. anomalum in the G. hirsutum background. This set of CSSLs included 70 homozygous substitutions and four heterozygous substitutions, and it collectively contained about 72.22% of the G. anomalum genome. Twenty-four quantitative trait loci associated with plant height, yield, and fiber qualities were detected on 15 substitution segments. Integrating the reference genome with agronomic trait evaluation of the CSSLs enabled location and cloning of two G. anomalum genes that encode peroxiredoxin and putative callose synthase 8, respectively, conferring drought tolerance and improving fiber strength. We have demonstrated the power of a high-quality wild-species reference genome for identifying agronomically valuable alleles to facilitate interspecific introgression breeding in crops.

Tannin-Based Copolymer Resins: Synthesis and Characterization by Solid State 13C NMR and FT-IR Spectroscopy

In recent years, the interest for bio-sources is rising exponentially and tannins extracts are one of the most interesting, easily-available, phenolic building blocks. The condensed tannins or proanthocyanidins are already known for their polymerization chemistry, which is the basis for several natural-based materials (e.g., adhesives, foams). In the present work we aim to observe the behavior of the extract of Acacia Mimosa (Acacia mearnsii) when reacted with several possible co-monomers at different relative amount, pH and temperature conditions. The more insoluble copolymers obtained with formaldehyde, hexamine, glyoxal, maleic anhydride, furfural and furfuryl alcohol were analyzed through solid state 13C NMR (Nuclear magnetic resonance) and FT-IR (Fourier Transform-Infrared) spectroscopy. The 13C NMR afforded the opportunity to detect: (i) aromatic substitutions and consequent poly-condensations for the majority of the hardeners studied; (ii) acylation for the maleic anhydride and also some; (iii) Diels⁻Alder arrangements for the furanic co-monomers; the FT-IR spectroscopy suggested that the formaldehyde and hexamine copolymers present a higher cross-linking degree.

ANK, a host cytoplasmic receptor for the Tobacco mosaic virus cell-to-cell movement protein, facilitates intercellular transport through plasmodesmata

Plasmodesma (PD) is a channel structure that spans the cell wall and provides symplastic connection between adjacent cells. Various macromolecules are known to be transported through PD in a highly regulated manner, and plant viruses utilize their movement proteins (MPs) to gate the PD to spread cell-to-cell. The mechanism by which MP modifies PD to enable intercelluar traffic remains obscure, due to the lack of knowledge about the host factors that mediate the process. Here, we describe the functional interaction between Tobacco mosaic virus (TMV) MP and a plant factor, an ankyrin repeat containing protein (ANK), during the viral cell-to-cell movement. We utilized a reverse genetics approach to gain insight into the possible involvement of ANK in viral movement. To this end, ANK overexpressor and suppressor lines were generated, and the movement of MP was tested. MP movement was facilitated in the ANK-overexpressing plants, and reduced in the ANK-suppressing plants, demonstrating that ANK is a host factor that facilitates MP cell-to-cell movement. Also, the TMV local infection was largely delayed in the ANK-suppressing lines, while enhanced in the ANK-overexpressing lines, showing that ANK is crucially involved in the infection process. Importantly, MP interacted with ANK at PD. Finally, simultaneous expression of MP and ANK markedly decreased the PD levels of callose, β-1,3-glucan, which is known to act as a molecular sphincter for PD. Thus, the MP-ANK interaction results in the downregulation of callose and increased cell-to-cell movement of the viral protein. These findings suggest that ANK represents a host cellular receptor exploited by MP to aid viral movement by gating PD through relaxation of their callose sphincters.

Response of the enzymes to nitrogen applications in cotton fiber (Gossypium hirsutum L.) and their relationships with fiber strength

To investigate the response of key enzymes to nitrogen (N) rates in cotton fiber and its relationship with fiber strength, experiments were conducted in 2005 and 2006 with cotton cultivars in Nanjing. Three N rates 0, 240 and 480 kgN/hm(2), signifying optimum and excessive nitrogen application levels were applied. The activities and the gene expressions of the key enzymes were affected by N, and the characteristics of cellulose accumulation and fiber strength changed as the N rate varied. Beta-1,3-glucanase activity in cotton fiber declined from 9 DPA till boll opening, and the beta-1, 3-glucanase coding gene expression also followed a unimodal curve in 12-24 DPA. In 240 kgN/hm(2) condition, the characteristics of enzyme activity and gene expression manner for sucrose synthase and beta-1,3-glucanase in developing cotton fiber were more favorable for forming a longer and more steady cellulose accumulation process, and for high strength fiber development.

Cellulose microfibrils in plants: biosynthesis, deposition, and integration into the cell wall

Cellulose occurs in all higher plants and some algae, fungi, bacteria, and animals. It forms microfibrils containing the crystalline allomorphs, cellulose I alpha and I beta. Cellulose molecules are 500-15,000 glucose units long. What controls molecular size is unknown. Microfibrils are elongated by particle rosettes in the plasma membrane (cellulose synthase complexes). The precursor, UDP-glucose, may be generated from sucrose at the site of synthesis. The biosynthetic mechanism may involve lipid-linked intermediates. Cellulose synthase has been purified from bacteria, but not from plants. In plants, disrupted cellulose synthase may form callose. Cellulose synthase genes have been isolated from bacteria and plants. Cellulose-deficient mutants have been characterised. The deduced amino acid sequence suggests possible catalytic mechanisms. It is not known whether synthesis occurs at the reducing or nonreducing end. Endoglucanase may play a role in synthesis. Nascent cellulose molecules associate by Van der Waals and hydrogen bonds to form microfibrils. Cortical microtubules control microfibril orientation, thus determining the direction of cell growth. Self-assembly mechanisms may operate. Microfibril integration into the wall occurs by interactions with matrix polymers during microfibril formation.

Movement of plant viruses is delayed in a beta-1,3-glucanase-deficient mutant showing a reduced plasmodesmatal size exclusion limit and enhanced callose deposition

Susceptibility to virus infection is decreased in a class I beta-1,3-glucanase (GLU I)-deficient mutant (TAG4.4) of tobacco generated by antisense transformation. TAG4.4 exhibited delayed intercellular trafficking via plasmodesmata of a tobamovirus (tobacco mosaic virus), of a potexvirus (recombinant potato virus X expressing GFP), and of the movement protein (MP) 3a of a cucumovirus (cucumber mosaic virus). Monitoring the cell-to-cell movement of dextrans and peptides by a novel biolistic method revealed that the plasmodesmatal size exclusion limit (SEL) of TAG4.4 was also reduced from 1.0 to 0.85 nm. Therefore, GLU I-deficiency has a broad effect on plasmodesmatal movement, which is not limited to a particular virus type. Deposition of callose, a substrate for beta-1,3-glucanases, was increased in TAG4.4 in response to 32 degrees C treatment, treatment with the fungal elicitor xylanase, and wounding, suggesting that GLU I has an important function in regulating callose metabolism. Callose turnover is thought to regulate plasmodesmatal SEL. We propose that GLU I induction in response to infection may help promote MP-driven virus spread by degrading callose.

The function of vacuolar beta-1,3-glucanase investigated by antisense transformation. Susceptibility of transgenic Nicotiana sylvestris plants to Cercospora nicotianae infection

Vacuolar class I beta-1,3-glucanases (EC 3.2.1.39) are believed to be important in the induced defense reaction of plants to fungal infection. We used antisense transformation to test this hypothesis and to identify other possible physiological functions of this enzyme. Nicotiana sylvestris plants were transformed with antisense constructions containing the region from position 27 to 608 of the coding sequence of the basic, vacuolar beta-1,3-glucanase gene GLA of tobacco regulated by cauliflower mosaic virus 35S RNA expression signals. Plants homozygous for this transgene showed a marked, ca. 20-fold reduction in the constitutive expression of class I beta-1,3-glucanase antigen in their leaves. RNA blot analysis indicated that the antisense plants expressed low levels of the sense transcript of the host beta-1,3-glucanase gene and the antisense transcript of the transgene. Immune blot analysis of plant extracts indicated that only expression of the N. sylvestris homologue of class I tobacco beta-1,3-glucanase and not the acidic, class II isoforms of the enzyme was blocked in the antisense plants. Class I isoforms of beta-1,3-glucanase and chitinase were coordinately induced in leaves of untransformed and empty-vector-transformed N. sylvestris plants treated with ethylene or infected with the fungal leaf pathogen Cercospora nicotianae. In antisense plants, chitinase but not beta-1,3-glucanase was induced under these conditions indicating that antisense transformation effectively blocks constitutive as well as induced expression of class I beta-1,3-glucanase. Under greenhouse conditions, antisense plants developed normally and were fertile. The plants did not exhibit increased susceptibility to C. nicotianae infection. These results suggest that expression of the beta-1,3-glucanase isoform blocked by antisense transformation is not necessary for 'housekeeping' functions of N. sylvestris nor defense against the fungal pathogen tested.

Developmental and hormonal regulation of β-1,3-glucanase in tobacco

A highly sensitive and specific "rocket" immunoassay was used to measure the content of an endo-type β-1,3-glucanase (EC 3.2.1.39) in tissues of Nicotiana tabacum L. cv. Havana 425. We show that the accumulation of β-1,3-glucanase in cultured pith-parenchyma tissue is blocked by combinations of the auxin, α-naphthaleneacetic acid (NAA), and the cytokinin, kinetin. When tissues pre-incubated for 7 d on complete medium containing 2.0 mg·l(-1) NAA and 0.3 mg·l(-1) kinetin are transferred onto medium without hormones or with either hormone added separately, the β-1,3-glucanase content expressed per mg soluble protein increases approx. ten fold over a 7-d period. Under these inductive conditions, up to approx. 5% of the soluble protein is β-1,3-glucanase. The induction is inhibited by >90% when tissues are cultured over the same period on medium containing both hormones. This β-1,3-glucanase is developmentally regulated in the intact plant. It is a major component of the soluble protien in the lower leaves and roots but is not detectable in leaves near the top of the plant.

β-Glucanases in developing cotton (Gossypium hirsutum L.) fibres

Cotton fibres possess several β-glucanase activities which appear to be associated with the cell wall, but which can be partially solubilised in buffers. The main activity detected was that of an exo-(1→3)-β-D-glucanase (EC 3.2.1.58) but which also had the characteristics of a β-glucosidase (EC 3.2.1.21). Endo-(1→3)-β-D-glucanase activity (EC 3.2.1.39) and much lower levels of (1→4)-β-D-glucanase activity were also detected. The exo-(1→3)-β-glucanase showed a maximum late on (40 days post-anthesis) in the development of the fibres, whereas the endo-(1→3)-β-glucanase activity remained constant throughout fibre development. The β-glucanase complex associated with the cotton-fibre cell wall also functions as a transglucosylase introducing, inter alia, (1→6)-β-glucosyl linkages into the disaccharide cellobiose to give the trisaccharide 4-O-β-gentiobiosylglucose.

Influence of external factors on callose and cellulose synthesis during incubation in vitro of intact cotton fibres with [(14)C]sucrose

Seed clusters, with adhering fibres, from individual locules of 36-d-old fruit capsules of Gossypium arboreum L. were fed with [(14)C]sucrose in vitro. The fibres synthesised, under standard conditions, (1→3)-β-D-glucan (callose) and (1→4)-β-D-glucan (cellulose) in the ratio of approx. 2:1. Under a great variety of different conditions this product ratio remained more or less constant, even when total glucan synthesis was strongly inhibited with 2,4-dinitrophenol or phloretin, or when stimulated with abscisic acid. In attempts to favour cellulose synthesis, no conditions were found where the ratio was substantially reduced. On the other hand, the ratio could be appreciably increased by inhibiting cellulose synthesis, e.g. with 2,6-dichlorobenzonitrile or coumarin, by anionic detergents such as sodium dodecyl sulphate, by low temperatures, or by increasing the osmotic strength of the incubation medium up to conditions causing plasmolysis. Specific degradation of callose, during incubation of the seed clusters, by exogenous exo-(1→3)-β-D-glucanase significantly diminished incorporation of radioactivity into cellulose.

Specific and direct measurement of theβ-1,3-glucan in developing cotton fiber

The reaction of N,N-diethylaziridinium chloride with raw cotton (Gossypium hirsutum L.) seed fibers to introduce N,N-diethylaminoethyl (DEAE) substituents at a low degree of substitution was used for demonstrating the presence of O(4)H, characteristic of a β-1,3-glucan. The derivatized 1,3-glucan/cellulose was hydrolyzed to DEAE-glucoses that were analyzed by gas-liquid chromatography. Capillary columns proved effective for measuring the small amounts of 4-O-DEAE-glucose in the presence of major amounts of 2-O- and 6-O-DEAE-glucoses. Analyses of raw cotton fibers were carried out through fiber development (20, 27, 34, 41 and 48 d post anthesis, DPA) and field exposure (62, 83 and 104 DPA) periods. The yields of 4-O- and other individual DEAE-glucoses and the yield of 4-O-DEAE-glucose in relation to 2-O-DEAE-glucose were particularly informative concenring the role of the β-1,3-glucan in cellulose. The results confirmed the early production and almost immediate decrease of the β-1,3-glucan and demonstrated continued production of accessible cellulose followed by a sharp decrease in accessibility after boll opening. The β-1,3-glucan content of the raw cotton fiber, estimated from the yield of 4-O-DEAE-glucose (representing 1,3-glucan) and the yield of 2-O-DEAE-glucose (approximating 1,3-glucan plus cellulose) was 10%, 4%, 1% and 0.6% at, in the order given, 20, 27, 48, and 104 DPA. These results are in general agreement with other conventional analyses.

Changes in the non-structural carbohydrate content of cotton (Gossypium spp.) fibres at different stages of development

The neutral sugars (glucose, fructose, and sucrose) and the sugar phosphates (glucose 6-phosphate, glucose 1-phosphate and fructose 6-phosphate) soluble in hot aqueous 80% methanol from the fibres of cotton - Gossypium arboreum L., G. barbadense L., and G. hirsutum L. - were determined at various stages of fibre development. In addition, the (1→3)-β-D-glucan content was measured and in the case of G. arboreum the rate of (1→3)-β-D-glucan and cellulose synthesis was determined with [(14)C]sucrose as the precursor. For each of the species a similar chronology was obtained for the changes in content of the various non-structural carbohydrates. At the early stages of secondary wall formation, glucose and fructose exhibited a maximum which was closely followed by a maximum in the (1→3)-β-D-glucan content and in the sugar phosphates. On the other hand, the sucrose content increased regularly until fibre maturity. The rates of synthesis of (1→3)-β-D-glucan and of cellulose were highest following the maximum in the (1→3)-β-D-glucan content, when the latter was being depleted.