Yaseen Mottiar

Designer lignins: harnessing the plasticity of lignification

Lignin is a complex polyphenolic constituent of plant secondary cell walls. Inspired largely by the recalcitrance of lignin to biomass processing, plant engineering efforts have routinely sought to alter lignin quantity, composition, and structure by exploiting the inherent plasticity of lignin biosynthesis. More recently, researchers are attempting to strategically design plants for increased degradability by incorporating monomers that lead to a lower degree of polymerisation, reduced hydrophobicity, fewer bonds to other cell wall constituents, or novel chemically labile linkages in the polymer backbone. In addition, the incorporation of value-added structures could help valorise lignin. Designer lignins may satisfy the biological requirement for lignification in plants while improving the overall efficiency of biomass utilisation.

Effects of PHENYLALANINE AMMONIA LYASE (PAL) knockdown on cell wall composition, biomass digestibility, and biotic and abiotic stress responses in Brachypodium

Highlight Reducing the function of PAL, the first enzyme in the phenylpropanoid pathway, in Brachypodium distachyon alters cell wall composition, increases fungal susceptibility, but minimally affects caterpillar herbivory and abiotic stress tolerance.

Effect of compost, nitrogen salts, and NPK fertilizers on methane oxidation potential at different temperatures

The effects of compost, nitrogen salts, and nitrogen–phosphorous–potassium (NPK) fertilizers on the methane oxidation potential (MOP) of landfill cover soil at various temperatures were assessed. For this, we used batch assays conducted at 5°C, 15°C, and 25°C with microcosms containing landfill cover soil slurries amended with these elements. Results indicated variable impacts dependent on the type of amendment and the incubation temperature. For a given incubation temperature, MOP varied from one compost to another and with the amount of compost added, except for the shrimp/peat compost. With this latter compost, independent of the amount, MOP values remained similar and were significantly higher than those obtained with other composts. Amendment with most of the tested nitrogen salts led to similar improvements in methanotrophic activity, except for urea. MOP with NPK fertilizer addition was amongst the highest in this study; the minimum value obtained with NPK (20–0–20) suggested the importance of P for methanotrophs. MOP generally increased with temperature, and nutrient limitation became less important at higher temperatures. Overall, at each of the three temperatures tested, MOP with NPK fertilizer amendments provided the best results and was comparable to those observed with the addition of the shrimp/peat compost. The results of this study provide the first evidence of the following: (1) compost addition to improve methanotrophic activity in a landfill cover soil should consider the amount and type of compost used and (2) the importance of using NPK fertilizers rather than nitrogen salts, in enhancing this activity, primarily at low temperatures. One can also consider the potential beneficial impact of adding these elements to enhance plant growth, which is an advantage for MOP.

Expression of the nos operon proteins from Pseudomonas stutzeri in transgenic plants to assemble nitrous oxide reductase.

Nitrous oxide (N2O) is a stable greenhouse gas that plays a significant role in the destruction of the ozone layer. Soils are a significant source of atmospheric N2O. It is important to explore some innovative and effective biology-based strategies for N2O mitigation. The enzyme nitrous oxide reductase (N2OR), naturally found in soil bacteria, is responsible for catalysing the final step of the denitrification pathway, conversion of N2O to dintrogen gas (N2). To transfer this catalytic pathway from soil into plants and amplify the abundance of this essential mechanism (to reduce global warming), a mega-cassette of five coding sequences was assembled to produce transgenic plants heterologously expressing the bacterial nos operon in plant leaves. Both the single-gene transformants (nosZ) and the multi-gene transformants (nosFLZDY) produced active recombinant N2OR. Enzymatic activity was detected using the methyl viologen-linked enzyme assay, showing that extracts from both types of transgenic plants exhibited N2O-reducing activity. Remarkably, the single-gene strategy produced higher reductase capability than the whole-operon approach. The data indicate that bacterial N2OR expressed in plants could convert N2O into inert N2 without involvement of other Nos proteins. Silencing by homologous signal sequences, or cryptic intracellular targeting are possible explanations for the low activities obtained. Expressing N2OR from Pseudomonas stutzeri in single-gene transgenic plants indicated that such ag-biotech solutions to climate change have the potential to be easily incorporated into existing genetically modified organism seed germplasm.

A novel nitrous oxide mitigation strategy: expressing nitrous oxide reductase from Pseudomonas stutzeri in transgenic plants

Wan, S., Greenham, T., Goto, K., Mottiar, Y., Johnson, A. M., Staebler, J. M., Zaidi, M. A., Shu, Q. and Altosaar, I. 2014. A novel nitrous oxide mitigation strategy: expressing nitrous oxide reductase from Pseudomonas stutzeri in transgenic plants. Can. J. Plant Sci. 94: 1013-1025. As a stable greenhouse gas, nitrous oxide (N2O) plays a significant role in stratospheric ozone destruction. The primary anthropogenic N2O source is the use of nitrogen in agriculture. Currently, the annual N2O emissions from this soil-plant-microbial system is more than 2.6 Tg (1 Tg=1 million metric tonnes) of N2O-N globally. So it is important to explore some innovative and effective biology-based strategies for N2O mitigation. If shown to be effective in field trails as well as laboratory-scale experiments, such GMO plants could help guide international policies on adaptation to climate change. The bacterial enzyme nitrous oxide reductase (N2OR) is the only known enzyme capable of catalyzing the final step of the denitrification pathway, conversion of N2O to N2. To “scrub” the N2O emissions, bacterial N2OR was heterologously expressed in plants. Structurally, the enzyme N2OR is encoded by nosZ, but its biosynthesis and assembly in prokaryotes require the products of several nos genes, including a putative ABC-type transporter encoded by nosDFY, and the copper chaperone NosL for biogenesis of the metal centre. We have generated transgenic tobacco plants expressing the nosZ gene, as well as tobacco plants in which the other nos genes were co-expressed under the control of a root-specific promoter (rolD) and a constitutive promoter (d35S). The nosZ gene from Pseudomonas stutzeri heterologously expressed in tobacco produced active recombinant N2OR. The positive results in the preliminary proof-of-principle experiments indicated that plants heterologously expressing N2OR could mitigate emissions at the source before N2O reaches the stratosphere or troposphere.

Bacterial nitrous oxide reductase expressed in transgenic plants: Evidence for sufficient anaerobicity to permit activity

Wan, S., Goto, K., Mottiar, Y., Staebler, J. M., Johnson, A. M., Voronova, A., Blais, D. R., Zaidi, M. A. and Altosaar, I. 2012. Bacterial nitrous oxide reductase expressed in transgenic plants: Evidence for sufficient anaerobicity to permit activity. Can. J. Plant Sci. 92: 1283-1294. Soil nitrogen enrichment practices enhance crop yields but greatly exacerbate the production and release of nitrous oxide (N2O), a potent greenhouse gas. The conversion of N2O to dinitrogen (N2) in soil denitrifiers is normally driven by the anaerobic enzyme nitrous oxide reductase (N2OR). Since this step is often limited in fertilised soils, we have transferred this unique microbial biocatalyst from the soil bacterium Pseudomonas stutzeri to transgenic Nicotiana tabacum plants. Our results confirm that engineered plants expressing the N2OR structural gene nosZ are capable of producing functional reductase enzyme without the involvement of the native accessory gene products. Since bacterial N2OR normally exists in the anaerobic environment of the soil bacteriums periplasmic space, this novel in planta activity suggests that plant cells can provide a similar hypoxic refuge for anaerobic enzyme activity. Genetically engineered crops containing N2OR could have considerable potential in the phytoremediation of atmospheric N2O.