The cell wall provides external support of the plant cells, while the cytoskeletons including the microtubules and the actin filaments constitute an internal framework. The cytoskeletons contribute to the cell wall biosynthesis by spatially and temporarily regulating the transportation and deposition of cell wall components. This tight control is achieved by the dynamic behavior of the cytoskeletons, but also through the tethering of these structures to the plasma membrane. This tethering may also extend beyond the plasma membrane and impact on the cell wall, possibly in the form of a feedback loop. In this review, we discuss the linking components between the cytoskeletons and the plasma membrane, and/or the cell wall. We also discuss the prospective roles of these components in cell wall biosynthesis and modifications, and aim to provide a platform for further studies in this field.

Liu Z, Persson S, Zhang Y (2015) The connection of cytoskeletal network with plasma membrane and the cell wall. J Integr Plant Biol 57: 330–340 doi: 10.1111/jipb.12342

Secondarily thickened cell walls of water-conducting vessels and tracheids and support-giving sclerenchyma cells contain lignin that makes the cell walls water impermeable and strong. To what extent laccases and peroxidases contribute to lignin biosynthesis in muro is under active evaluation. We performed an in silico study of Norway spruce (Picea abies (L.) Karst.) laccases utilizing available genomic data. As many as 292 laccase encoding sequences (genes, gene fragments, and pseudogenes) were detected in the spruce genome. Out of the 112 genes annotated as laccases, 79 are expressed at some level. We isolated five full-length laccase cDNAs from developing xylem and an extracellular lignin-forming cell culture of spruce. In addition, we purified and biochemically characterized one culture medium laccase from the lignin-forming cell culture. This laccase has an acidic pH optimum (pH 3.8–4.2) for coniferyl alcohol oxidation. It has a high affinity to coniferyl alcohol with an apparent K_m value of 3.5 μM; however, the laccase has a lower catalytic efficiency (V_max/K_m) for coniferyl alcohol oxidation compared with some purified culture medium peroxidases. The properties are discussed in the context of the information already known about laccases/coniferyl alcohol oxidases of coniferous plants.

Koutaniemi S, Malmberg HA, Simola LK, Teeri TH, Kärkönen A (2015) Norway spruce (Picea abies) laccases: Characterization of a laccase in a lignin-forming tissue culture. J Integr Plant Biol 57: 341–348 doi: 10.1111/jipb.12333

Plant class III heme peroxidases catalyze lignin polymerization. Previous reports have shown that at least three Arabidopsis thaliana peroxidases, AtPrx2, AtPrx25 and AtPrx71, are involved in stem lignification using T-DNA insertion mutants, atprx2, atprx25, and atprx71. Here, we generated three double mutants, atprx2/atprx25, atprx2/atprx71, and atprx25/atprx71, and investigated the impact of the simultaneous deficiency of these peroxidases on lignins and plant growth. Stem tissue analysis using the acetyl bromide method and derivatization followed by reductive cleavage revealed improved lignin characteristics, such as lowered lignin content and increased arylglycerol-β-aryl (β-O-4) linkage type, especially β-O-4 linked syringyl units, in lignin, supporting the roles of these genes in lignin polymerization. In addition, none of the double mutants exhibited severe growth defects, such as shorter plant stature, dwarfing, or sterility, and their stems had improved cell wall degradability. This study will contribute to progress in lignin bioengineering to improve lignocellulosic biomass.

Shigeto J, Itoh Y, Hirao S, Ohira K, Fujita K, Tsutsumi Y (2015) Simultaneously disrupting AtPrx2, AtPrx25 and AtPrx71 alters lignin content and structure in Arabidopsis stem. J Integr Plant Biol 57: 349–356 doi: 10.1111/jipb.12334

Maize (Zea mays L.) suspension-cultured cells with up to 70% less cellulose were obtained by stepwise habituation to dichlobenil (DCB), a cellulose biosynthesis inhibitor. Cellulose deficiency was accompanied by marked changes in cell wall matrix polysaccharides and phenolics as revealed by Fourier transform infrared (FTIR) spectroscopy. Cell wall compositional analysis indicated that the cellulose-deficient cell walls showed an enhancement of highly branched and cross-linked arabinoxylans, as well as an increased content in ferulic acid, diferulates and p-coumaric acid, and the presence of a polymer that stained positive for phloroglucinol. In accordance with this, cellulose-deficient cell walls showed a fivefold increase in Klason-type lignin. Thioacidolysis/GC-MS analysis of cellulose-deficient cell walls indicated the presence of a lignin-like polymer with a Syringyl/Guaiacyl ratio of 1.45, which differed from the sensu stricto stress-related lignin that arose in response to short-term DCB-treatments. Gene expression analysis of these cells indicated an overexpression of genes specific for the biosynthesis of monolignol units of lignin. A study of stress signaling pathways revealed an overexpression of some of the jasmonate signaling pathway genes, which might trigger ectopic lignification in response to cell wall integrity disruptions. In summary, the structural plasticity of primary cell walls is proven, since a lignification process is possible in response to cellulose impoverishment.

Mélida H, Largo-Gosens A, Novo-Uzal E, Santiago R, Pomar F, García P, García-Angulo P, Acebes JL, Álvarez J, Encina A (2015) Ectopic lignification in primary cellulose-deficient cell walls of maize cell suspension cultures. J Integr Plant Biol 57: 357–372 doi: 10.1111/jipb.12346

Cell-suspension cultures (Zea mays L., Black Mexican sweet corn) habituated to 2,6-dichlorobenzonitrile (DCB) survive with reduced cellulose owing to hemicellulose network modification. We aimed to define the hemicellulose metabolism modifications in DCB-habituated maize cells showing a mild reduction in cellulose at different stages in the culture cycle. Using pulse-chase radiolabeling, we fed habituated and non-habituated cultures with [³H]arabinose, and traced the distribution of ³H-pentose residues between xylans, xyloglucans and other polymers in several cellular compartments for 5 h. Habituated cells were slower taking up exogenous [³H]arabinose. Tritium was incorporated into polysaccharide-bound arabinose and xylose residues, but habituated cells diverted a higher proportion of their new [³H]xylose residues into (hetero) xylans at the expense of xyloglucan synthesis. During logarithmic growth, habituated cells showed slower vesicular trafficking of polymers, especially xylans. Moreover, habituated cells showed a decrease in the strong wall-binding of all pentose-containing polysaccharides studied; correspondingly, especially in log-phase cultures, habituation increased the proportion of ³H-hemicelluloses ([³H]xylans and [³H]xyloglucan) sloughed into the medium. These findings could be related to the cell walls' cellulose-deficiency, and consequent reduction in binding sites for hemicelluloses; the data could also reflect the habituated cells' reduced capacity to integrate arabinoxylans by extra-protoplasmic phenolic cross-linking, as well as xyloglucans, during wall assembly.

de Castro M, Miller JG, Acebes JL, Encina A, García-Angulo P, Fry SC (2015) The biosynthesis and wall-binding of hemicelluloses in cellulose-deficient maize cells: An example of metabolic plasticity. J Integr Plant Biol 57: 373–387 doi: 10.1111/jipb.12331

We studied in detail the mean microfibril angle and the width of cellulose crystals from the pith to the bark of a 15-year-old Maidenhair tree (Ginkgo biloba L.). The orientation of cellulose microfibrils with respect to the cell axis and the width and length of cellulose crystallites were determined using X-ray diffraction. Raman microscopy was used to compare the lignin distribution in the cell wall of normal/opposite and compression wood, which was found near the pith. Ginkgo biloba showed a relatively large mean microfibril angle, varying between 19° and 39° in the S2 layer, and the average width of cellulose crystallites was 3.1–3.2 nm. Mild compression wood without any intercellular spaces or helical cavities was observed near the pith. Slit-like bordered pit openings and a heavily lignified S2L layer confirmed the presence of compression wood. Ginkgo biloba showed typical features present in the juvenile wood of conifers. The microfibril angle remained large over the 14 annual rings. The entire stem disc, with a diameter of 18 cm, was considered to consist of juvenile wood. The properties of juvenile and compression wood as well as the cellulose orientation and crystalline width indicate that the wood formation of G. biloba is similar to that of modern conifers.

Andersson S, Wang Y, Pönni R, Hänninen T, Mononen M, Ren H, Serimaa R, Saranpää P (2015) Cellulose structure and lignin distribution in normal and compression wood of the Maidenhair tree (Ginkgo biloba L.). J Integr Plant Biol 57: 388–395 doi: 10.1111/jipb.12349

Glass M, Barkwill S, Unda F, Mansfield SD (2015) Endo-b-1,4-glucanases impact plant cell wall development by influencing cellulose crystallization. J Integr Plant Biol 57: 396–410 doi: 10.1111/jipb.12353

Transglycanases (endotransglycosylases) cleave a polysaccharide (donor-substrate) in mid-chain, and then transfer a portion onto another poly- or oligosaccharide (acceptor-substrate). Such enzymes contribute to plant cell-wall assembly and/or re-structuring. We sought a general method for revealing novel homo- and hetero-transglycanases, applicable to diverse polysaccharides and oligosaccharides, separating transglycanase-generated ³H-polysaccharides from unreacted ³H-oligosaccharides—the former immobilized (on filter-paper, silica-gel or glass-fiber), the latter eluted. On filter-paper, certain polysaccharides [e.g. (13, 14)-β-d-glucans] remained satisfactorily adsorbed when water-washed; others (e.g. pectins) were partially lost. Many oligosaccharides (e.g. arabinan-, galactan-, xyloglucan-based) were successfully eluted in appropriate solvents, but others (e.g. [³H]xylohexaitol, [³H]mannohexaitol [³H]cellohexaitol) remained immobile. On silica-gel, all ³H-oligosaccharides left an immobile ‘ghost’ spot (contaminating any ³H-polysaccharides), which was diminished but not prevented by additives e.g. sucrose or Triton X-100. The best stratum was glass-fiber (GF), onto which the reaction-mixture was dried then washed in 75% ethanol. Washing led to minimal loss or lateral migration of ³H-polysaccharides if conducted by slow percolation of acidified ethanol. The effectiveness of GF-blotting was well demonstrated for Chara vulgaris trans-β-mannanase. In conclusion, our novel GF-blotting technique efficiently frees transglycanase-generated ³H-polysaccharides from unreacted ³H-oligosaccharides, enabling high-throughput screening of multiple postulated transglycanase activities utilising chemically diverse donor- and acceptor-substrates.

Franková L, Fry SC (2015) A general method for assaying homo- and hetero-transglycanase activities that act on plant cell-wall polysaccharides. J Integr Plant Biol 57: 411–428 doi: 10.1111/jipb.12337

In cereals, the presence of soluble polysaccharides including (1,3;1,4)-β-glucan has downstream implications for human health, animal feed and biofuel applications. Sorghum bicolor (L.) Moench is a versatile crop, but there are limited reports regarding the content of such soluble polysaccharides. Here, the amount of (1,3;1,4)-β-glucan present in sorghum tissues was measured using a Megazyme assay. Very low amounts were present in the grain, ranging from 0.16%–0.27% (w/w), while there was a greater quantity in vegetative tissues at 0.12–1.71% (w/w). The fine structure of (1,3;1,4)-β-glucan, as denoted by the ratio of cellotriosyl and cellotetraosyl residues, was assessed by high performance liquid chromatography (HPLC) and ranged from 2.6–3:1 in the grain, while ratios in vegetative tissues were lower at 2.1–2.6:1. The distribution of (1,3;1,4)-β-glucan was examined using a specific antibody and observed with fluorescence and transmission electron microscopy. Micrographs showed a variable distribution of (1,3;1,4)-β-glucan influenced by temporal and spatial factors. The sorghum orthologs of genes implicated in the synthesis of (1,3;1,4)-β-glucan in other cereals, such as the Cellulose synthase-like (Csl) F and H gene families were defined. Transcript profiling of these genes across sorghum tissues was carried out using real-time quantitative polymerase chain reaction, indicating that, as in other cereals, CslF6 transcripts dominated.