Abstract
BackgroundOne of the major barriers to the development of lignocellulosic feedstocks is the recalcitrance of plant cell walls to deconstruction and saccharification. Recalcitrance can be reduced by targeting genes involved in cell wall biosynthesis, but this can have unintended consequences that compromise the agronomic performance of the trees under field conditions. Here we report the results of a field trial of fourteen distinct transgenic Populus deltoides lines that had previously demonstrated reduced recalcitrance without yield penalties under greenhouse conditions.ResultsSurvival and productivity of the trial were excellent in the first year, and there was little evidence for reduced performance of the transgenic lines with modified target gene expression. Surprisingly, the most striking phenotypic effects in this trial were for two empty-vector control lines that had modified bud set and bud flush. This is most likely due to somaclonal variation or insertional mutagenesis. Traits related to yield, crown architecture, herbivory, pathogen response, and frost damage showed few significant differences between target gene transgenics and empty vector controls. However, there were a few interesting exceptions. Lines overexpressing the DUF231 gene, a putative O-acetyltransferase, showed early bud flush and marginally increased height growth. Lines overexpressing the DUF266 gene, a putative glycosyltransferase, had significantly decreased stem internode length and slightly higher volume index. Finally, lines overexpressing the PFD2 gene, a putative member of the prefoldin complex, had a slightly reduced volume index.ConclusionsThis field trial demonstrates that these cell wall modifications, which decreased cell wall recalcitrance under laboratory conditions, did not seriously compromise first-year performance in the field, despite substantial challenges, including an outbreak of a stem boring insect (Gypsonoma haimbachiana), attack by a leaf rust pathogen (Melampsora spp.), and a late frost event. This bodes well for the potential utility of these lines as advanced biofuels feedstocks.
Highlights
One of the major barriers to the development of lignocellulosic feedstocks is the recalcitrance of plant cell walls to deconstruction and saccharification
Overall the results of this trial reflect well upon the transgenic lines that have emerged from the intensive screening process conducted by the Bioenergy Science Center (BESC)
Most lines have not shown any significant reductions in growth or tolerance of biotic or abiotic stresses in this field trial, despite several substantial challenges, including large outbreaks of the cottonwood twig borer and Melampsora leaf rust, as well as a late frost event
Summary
One of the major barriers to the development of lignocellulosic feedstocks is the recalcitrance of plant cell walls to deconstruction and saccharification. Macaya‐Sanz et al Biotechnol Biofuels (2017) 10:253 a feature of the cellulose polymer itself, which is packaged in tightly interconnected fibers that can be organized into crystalline sheets that themselves are relatively inaccessible to cellulolytic enzymes [1, 2]. These fibers occur within a largely hydrophobic matrix of lignin, which contributes to recalcitrance. The hemicelluloses and other non-cellulosic cell wall polymers may contribute to recalcitrance This structural complexity of the wall makes bioconversion of lignocellulosic biomass to liquid fuels challenging and expensive
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