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BACKGROUND: Lignin is an aromatic polymer deposited in secondary cell walls of higher plants to provide strength, rigidity, and hydrophobicity to vascular tissues. Due to its interconnections with cell wall polysaccharides, lignin plays important roles during plant growth and defense, but also has a negative impact on industrial processes aimed at obtaining monosaccharides from plant biomass. Engineering lignin offers a solution to this issue. For example, previous work showed that heterologous expression of a coliphage S-adenosylmethionine hydrolase (AdoMetase) was an effective approach to reduce lignin in the model plant Arabidopsis. The efficacy of this engineering strategy remains to be evaluated in bioenergy crops. RESULTS: We studied the impact of expressing AdoMetase on lignin synthesis in sorghum (Sorghum bicolor L. Moench). Lignin content, monomer composition, and size, as well as biomass saccharification efficiency were determined in transgenic sorghum lines. The transcriptome and metabolome were analyzed in stems at three developmental stages. Plant growth and biomass composition was further evaluated under field conditions. Results evidenced that lignin was reduced by 18% in the best transgenic line, presumably due to reduced activity of the S-adenosylmethionine-dependent O-methyltransferases involved in lignin synthesis. The modified sorghum features altered lignin monomer composition and increased lignin molecular weights. The degree of methylation of glucuronic acid on xylan was reduced. These changes enabled a ~20% increase in glucose yield after biomass pretreatment and saccharification compared to wild type. RNA-seq and untargeted metabolomic analyses evidenced some pleiotropic effects associated with AdoMetase expression. The transgenic sorghum showed developmental delay and reduced biomass yields at harvest, especially under field growing conditions. CONCLUSIONS: The expression of AdoMetase represents an effective lignin engineering approach in sorghum. However, considering that this strategy potentially impacts multiple S-adenosylmethionine-dependent methyltransferases, adequate promoters for fine-tuning AdoMetase expression will be needed to mitigate yield penalty.

[This corrects the article DOI: 10.1021/acssuschemeng.2c01160.].

Engineering bioenergy crops to accumulate value-added coproducts in planta is an attractive approach to increasing the value of lignocellulosic biomass and enabling a sustainable bioeconomy. In this study, we engineered sorghum with a bacterial gene encoding a dehydroshikimate dehydratase (qsuB) to convert the endogenous pool of 3-dehydroshikimate into the valuable compound protocatechuate (DHBA). We find that, when grown under field conditions, transgenic sorghum lines can accumulate up to 0.3% DHBA in stover on a dry weight (DW) basis without showing any difference in cell wall composition. An unexpected finding was an increase in yield for all qsuB-expressing lines. The grain yield and total biomass yield were 71 and 29% higher in the highest yielding line, respectively. On average, the total biomass yield of the engineered lines was 22.3 t/ha (DW). Moreover, we conducted a techno-economic analysis to investigate the economic impact of coproducing DHBA along with bioethanol in an integrated cellulosic biorefinery. Using engineered biomass sorghum with 0.3 DW% DHBA accumulated in planta as the feedstock, the economics of the integrated biorefineries has the potential to be improved. Our data demonstrate an engineering strategy to overproduce DHBA in bioenergy crops to facilitate sustainable manufacturing of biofuels and bioproducts.

BackgroundThe development of bioenergy crops with reduced recalcitrance to enzymatic degradation represents an important challenge to enable the sustainable production of advanced biofuels and bioproducts. Biomass recalcitrance is partly attributed to the complex structure of plant cell walls inside which cellulose microfibrils are protected by a network of hemicellulosic xylan chains that crosslink with each other or with lignin via ferulate (FA) bridges. Overexpression of the rice acyltransferase OsAT10 is an effective bioengineering strategy to lower the amount of FA involved in the formation of cell wall crosslinks and thereby reduce cell wall recalcitrance. The annual crop sorghum represents an attractive feedstock for bioenergy purposes considering its high biomass yields and low input requirements. Although we previously validated the OsAT10 engineering approach in the perennial bioenergy crop switchgrass, the effect of OsAT10 expression on biomass composition and digestibility in sorghum remains to be explored.ResultsWe obtained eight independent sorghum (Sorghum bicolor (L.) Moench) transgenic lines with a single copy of a construct designed for OsAT10 expression. Consistent with the proposed role of OsAT10 in acylating arabinosyl residues on xylan with p-coumarate (pCA), a higher amount of p-coumaroyl-arabinose was released from the cell walls of these lines upon hydrolysis with trifluoroacetic acid. However, no major changes were observed regarding the total amount of pCA or FA esters released from cell walls upon mild alkaline hydrolysis. Certain diferulate (diFA) isomers identified in alkaline hydrolysates were increased in some transgenic lines. The amount of the main cell wall monosaccharides glucose, xylose, and arabinose was unaffected. The transgenic lines showed reduced lignin content and their biomass released higher yields of sugars after ionic liquid pretreatment followed by enzymatic saccharification.ConclusionsExpression of OsAT10 in sorghum leads to an increase of xylan-bound pCA without reducing the overall content of cell wall FA esters. Nevertheless, the amount of total cell wall pCA remains unchanged indicating that most pCA is ester-linked to lignin. Unlike other engineered plants overexpressing OsAT10 or a phylogenetically related acyltransferase with similar putative function, the improvements of biomass saccharification efficiency in sorghum OsAT10 lines are likely the result of lignin reductions rather than reductions of cell wall-bound FA. These results also suggest a relationship between xylan-bound pCA and lignification in cell walls.

Plants have the potential to produce a wide array of secondary metabolites that have utility as drugs to treat human diseases. To tap this potential, functional human nuclear receptors have [...]

The promoters of genes encoding rice seed storage proteins (glutelin, prolamin, globulin and albumin) were analyzed for their ability to direct rβ-gIucuronidase (GUS) gene expression in transgenic rice plants. All promoters tested could direct endosperm-specific expression of the GUS reporter gene irrespective of variable activities and patterns in the endosperm. [ABSTRACT FROM AUTHOR]

Binding analyses revealed that the AAC--A sequence in glutelin gene promoters is the target site of OSMYB5 protein and that both the distal and proximal AACA motifs are recognized by this protein. These results suggest that the OSMYB5 protein functions as a trans-acting factor for glutelin gene expression. [ABSTRACT FROM AUTHOR]