Cell Wall Compositions of Sorghum bicolor Leaves and Roots Remain Relatively Constant Under Drought Conditions

An aggregated understanding of the influence of aqueous ammonia pretreatment on the physical deconstruction of cell walls in sugar beet pulp

The underlying interplay between physicochemical property and enzymatic hydrolysis of cellulose still remains unclear. The impacts of matrix glycan composition of sugar beet pulp (SBP) on physical structure and saccharification efficiency were emphasized. The results showed that aqueous ammonia (AA) pretreatment could remove the non-cellulosic polysaccharides and destroy the linkage between the pectin and lignin. The cellulose supramolecule was changed significantly after AA pretreatment, in terms of the decline in hardness, gumminess, springiness, thickness and degree of polymerization. Furthermore, vascular cell was exposed and degraded. The highest reducing sugar yield of 355.06 mg/g was obtained from the pretreated SBP (80 °C) with enzyme loading of 30 U/g, which was 1.01 times higher than that of the untreated SBP. This research also supported the idea that recognizing and precisely removing the primary epitopes in cell walls might be an ideal strategy to accomplish the improved enzymatic hydrolysis through mild pretreatment.

GsNAC2 gene enhances saline-alkali stress tolerance by promoting plant growth and regulating glutathione metabolism in Sorghum bicolor

The quality and yields of Sorghum bicolo r plants are seriously affected by saline-alkali conditions. NAC (NAM, ATAF, and CUC) transcription factors are plant specific and have various functions in plant development and response to various stresses. To investigate how GsNAC2 functions in sorghum responses to saline-alkali treatment, the characteristics of GsNAC2 were analysed by bioinformatics methods, and NaHCO3 :Na2 CO3 (5:1, 75mM, pH 9.63) saline-alkali stress solution was applied when sorghum plants were 2weeks old. The research results show that GsNAC2 belongs to the NAC gene family. GsNAC2 was significantly induced by saline-alkali treatment and strongly expressed in sorghum leaves. GsNAC2 -overexpressing sorghum plants had increased plant height, dry weight, moisture content, root activity, leaf length, chlorophyll content, stomatal conductance, relative root activity, relative chlorophyll content, relative stomatal conductance, and relative transpiration rate after saline-alkali treatment. Lower H2 O2 and O2 - levels, relative permeability of the plasma membrane, and malondialdehyde (MDA) content were found in GsNAC2 -overexpressing sorghum. In transcriptome analysis, clusters of orthologous groups (COG) analysis showed that a high proportion of differentially-expressed genes (DEGs) participated in defence mechanisms at each processing time, and 18 DEGs related to synthetic glutathione were obtained. Gene expression analysis revealed that key genes in glutathione biosynthesis pathways were upregulated. GR and GSH-Px activities were increased, and GSH accumulated more with the overexpression of GsNAC2 after saline-alkali treatment. Furthermore, these results suggest that GsNAC2 acts as a potentially important regulator in response to saline-alkali stress and may be used in molecular breeding to improve crop yields under adverse environmental conditions.

Multivariate analysis and genetic dissection of staygreen and stem reserve mobilisation under combined drought and heat stress in wheat (Triticum aestivum L.)

Introduction: Abiotic stresses significantly reduce crop yield by adversely affecting many physio-biochemical processes. Several physiological traits have been targeted and improved for yield enhancement in limiting environmental conditions. Amongst them, staygreen and stem reserve mobilisation are two important mutually exclusive traits contributing to grain filling under drought and heat stress in wheat. Henceforth, the present study was carried out to identify the QTLs governing these traits and to identify the superiors' lines through multi-trait genotype-ideotype distance index (MGIDI) Methods: A mapping population consisting of 166 recombinant inbred lines (RILs) developed from a cross between HD3086 and HI1500 was utilized in this study. The experiment was laid down in alpha lattice design in four environmental conditions viz. Control, drought, heat and combined stress (heat and drought). Genotyping of parents and RILs was carried out with 35 K Axiom® array (Wheat breeder array). Results and Discussion: Medium to high heritability with a moderate to high correlation between traits was observed. Principal component analysis (PCA) was performed to derive latent variables in the original set of traits and the relationship of these traits with latent variables.From this study, 14 QTLs were identified, out of which 11, 2, and 1 for soil plant analysis development (SPAD) value, leaf senescence rate (LSR), and stem reserve mobilisation efficiency (SRE) respectively. Quantitative trait loci (QTLs) for SPAD value harbored various genes like Dirigent protein 6-like, Protein FATTY ACID EXPORT 3, glucan synthase-3 and Ubiquitin carboxyl-terminal hydrolase, whereas QTLs for LSR were found to contain various genes like aspartyl protease family protein, potassium transporter, inositol-tetrakisphosphate 1-kinase, and DNA polymerase epsilon subunit D-like. Furthermore, the chromosomal region for SRE was found to be associated with serine-threonine protein kinase. Serine-threonine protein kinases are involved in many signaling networks such as ABA mediated ROS signaling and acclimation to environmental stimuli. After the validation of QTLs in multilocation trials, these QTLs can be used for marker-assisted selection (MAS) in breeding programs.

Field performance of switchgrass plants engineered for reduced recalcitrance

Switchgrass (Panicum virgatum L.) is a promising perennial bioenergy crop that achieves high yields with relatively low nutrient and energy inputs. Modification of cell wall composition for reduced recalcitrance can lower the costs of deconstructing biomass to fermentable sugars and other intermediates. We have engineered overexpression of OsAT10, encoding a rice BAHD acyltransferase and QsuB, encoding dehydroshikimate dehydratase from Corynebacterium glutamicum, to enhance saccharification efficiency in switchgrass. These engineering strategies demonstrated low lignin content, low ferulic acid esters, and increased saccharification yield during greenhouse studies in switchgrass and other plant species. In this work, transgenic switchgrass plants overexpressing either OsAT10 or QsuB were tested in the field in Davis, California, USA for three growing seasons. No significant differences in the content of lignin and cell wall-bound p-coumaric acid or ferulic acid were detected in transgenic OsAT10 lines compared with the untransformed Alamo control variety. However, the transgenic overexpressing QsuB lines had increased biomass yield and slightly increased biomass saccharification properties compared to the control plants. This work demonstrates good performance of engineered plants in the field, and also shows that the cell wall changes in the greenhouse were not replicated in the field, emphasizing the need to validate engineered plants under relevant field conditions.

Evaluation of engineered low-lignin poplar for conversion into advanced bioproducts

BACKGROUND

Lignocellulosic resources are promising feedstocks for the manufacture of bio-based products and bioenergy. However, the inherent recalcitrance of biomass to conversion into simple sugars currently hinders the deployment of advanced bioproducts at large scale. Lignin is a primary contributor to biomass recalcitrance as it protects cell wall polysaccharides from degradation and can inhibit hydrolytic enzymes via non-productive adsorption. Several engineering strategies have been designed to reduce lignin or modify its monomeric composition. For example, expression of bacterial 3-dehydroshikimate dehydratase (QsuB) in poplar trees resulted in a reduction in lignin due to redirection of metabolic flux toward 3,4-dihydroxybenzoate at the expense of lignin. This reduction was accompanied with remarkable changes in the pools of aromatic compounds that accumulate in the biomass.

RESULTS

The impact of these modifications on downstream biomass deconstruction and conversion into advanced bioproducts was evaluated in the current study. Using ionic liquid pretreatment followed by enzymatic saccharification, biomass from engineered trees released more glucose and xylose compared to wild-type control trees under optimum conditions. Fermentation of the resulting hydrolysates using Rhodosporidium toruloides strains engineered to produce α-bisabolene, epi-isozizaene, and fatty alcohols showed no negative impact on cell growth and yielded higher titers of bioproducts (as much as + 58%) in the case of QsuB transgenics trees.

CONCLUSION

Our data show that low-recalcitrant poplar biomass obtained with the QsuB technology has the potential to improve the production of advanced bioproducts.