Suppression of the lignin biosynthetic gene CCR1 results in decreased lignin recalcitrance and increased digestibility

Suppression of the lignin biosynthetic gene CCR1 results in decreased lignin recalcitrance and increased digestibility

Maize ccr1 mutant plants display normal growth, increased “zip-lignin” content, and improved sugar release.

The Science

In this study, we examined features of a lignin biosynthetic mutant in maize that we hypothesized could result in an increase in the levels of more readily cleavable ester bonds (“zip-lignin”) in the lignin backbone. The maize ccr1 mutant displayed reduced total lignin content with no growth penalties, higher zip-lignin levels, and higher levels of sugar release.

The Impact

Suppressing CCR and thereby increasing available pools of substrate for zip-lignin production may be a viable lignin biosynthetic method for reducing recalcitrance and improving sugar release in various biofuel crops.

Summary

The cell wall polymer lignin provides structural support and rigidity to plant cell walls and the plant body. However, the recalcitrance associated with lignin impedes the extraction of polysaccharides from the cell wall for use in making plant-based biofuels and biomaterials. To build on recent success of the zip-lignin approach in which readily cleavable ester linkages are introduced into lignin, here we investigate maize plants with a mutation in the first gene in the lignin-specific biosynthetic pathway, CINNAMOYL-CoA REDUCTASE (CCR). Downregulation of the CCR1 gene was previously shown to result in a pool of feruloyl-CoA and its derivatives in dicots, a condition we hypothesize could result in higher zip-lignin levels in grasses. Here we analyzed a maize ccr1 insertion mutant. As anticipated for a mutation in the first lignin-specific gene in the phenylpropanoid pathway, the ccr1 mutation resulted in reduced monolignol biosynthesis and lower total lignin content; however, the reduced lignin phenotype did not negatively impact growth of the mutant plants. These ccr1 mutant plants revealed three- to five-fold higher levels of monolignol ferulates (or zips) compared to wild type. Furthermore, digestibility, as measured by glucose release, was significantly higher in ccr1 mutants than in wild-type plants. Increasing the pool of feruloyl-CoA available for conjugation with monolignols therefore could be a viable method for reducing recalcitrance and improving sugar release for other biofuel crops.

Contacts (BER PM)

N. Kent Peters
Program Manager, Office of Biological and Environmental Research
kent.peters@science.doe.gov, 301-903-5549

(PI Contact)

Rebecca Smith
University of Wisconsin - Madison
rasmith29@wisc.edu

John Ralph
University of Wisconsin - Madison
jralph@wisc.edu

Funding
This research was funded by the DOE Great Lakes Bioenergy Research Center (DOE Office of Science BER DE-FC02-07ER64494).

Publications

Smith, R. A. et al. “Suppression of CINNAMOYL-CoA REDUCTASE increases the level of monolignol ferulates incorporated into maize lignins.” Biotechnology for Biofuels 10, 109 (2017) [DOI: 10.1186/s13068-017-0793-1]. 

Related Links

https://biotechnologyforbiofuels.biomedcentral.com/articles/10.1186/s13068-017-0793-1

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