Plants have convergently evolved to use "zips" (chemically labile ester linkages) in their lignin polymers

Monolignol ferulate conjugates are naturally incorporated into plant lignins. 

The Science
With a sensitive analytical method for diagnostically detecting incorporation of chemically labile ester bonds introduced into lignin polymers by augmenting the prototypical monomers with monolignol ferulate conjugates (“zip monomers”), we reexamined the lignin of three plants known to produce such conjugates in their extractives and found that these plants also used monolignol ferulate conjugates in their lignification. This discovery prompted a survey of a set of plants representing spermatophytes or “seed plants,” including 13 gymnosperms and 54 angiosperms.  

The Impact
These findings provide evidence that “zip-lignins” – lignins derived, in part, from monolignol ferulate conjugates – have developed naturally via convergent evolution in diverse angiosperm lineages. Identifying plant lines with increased zip-lignin content, which are likely to be more easily and economically deconstructed, could provide superior sources of biomass for conversion to biofuels and bioproducts.

Angiosperms represent most of the terrestrial plants and are the primary research focus for the conversion of biomass to liquid fuels and co-products. Lignin limits our access to fibers and represents a large fraction of the chemical energy stored in plant cell walls. Recently, the incorporation of monolignol ferulates into lignin polymers was accomplished via the engineering of an exotic transferase into commercially relevant poplar. We report that various angiosperm species might have convergently evolved to natively produce lignins that incorporate monolignol ferulate conjugates. We show that this activity may be accomplished by a BAHD feruloyl–coenzyme A monolignol transferase, OsFMT1 (AT5), in rice and its orthologs in other grasses.

Contacts (BER PM)
N. Kent Peters
Program Manager, Office of Biological and Environmental Research, 301-903-5549

(PI Contact)
John Ralph
University of Wisconsin - Madison

This work was funded by the DOE Great Lakes Bioenergy Research Center (DOE BER Office of Science DE-FC02-07ER64494), DOE Feedstock Genomics (DOE Office of Science BER DE-SC006904), NSF Experimental Program to Stimulate Competitive Research (under grant no. EPS-0814361), Specific Cooperative Agreement (#58-3655-8-129f) with the U.S. Dairy Forage Research Center, U.S. Department of Agriculture–Agricultural Research Service, the DOE Energy Biosciences Program [(#DE-AI02-06ER64299 (2006), a doctoral scholarship from The University of Auckland, and the Samuel Roberts Noble Foundation.

Karlen, S.D. et al. “Monolignol ferulate conjugates are naturally incorporated into plant lignins.” Science Advances 2, e1600393 (2016) [DOI: 10.1126/sciadv.1600393].

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