|CASS, CYNTHIA - Illinois State University|
|PERALDI, ANTOINE - John Innes Center|
|MOTTIAR, YASEEN - University Of British Columbia|
|SANTORO, NICHOLAS - Michigan State University|
|KARLEN, STEVEN - University Of Wisconsin|
|BUKHMAN, YURY - University Of Wisconsin|
|THROWER, NICK - Michigan State University|
|BRUNO, LAURA - John Innes Center|
|MOSKVIN, OLEG - University Of Wisconsin|
|WILLHOIT, MEGAN - Illinois State University|
|RALPH, JOHN - University Of Wisconsin|
|MANSFIELD, SHAWN - University Of British Columbia|
|NICHOLSON, PAUL - John Innes Center|
|SEDBROOK, JOHN - Illinois State University|
|FOSTER, CLIFF - Michigan State University|
|PHUTANE, MEGHA - Illinois State University|
Submitted to: Journal of Experimental Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/11/2015
Publication Date: 6/20/2015
Citation: Cass, C.L., Peraldi, A., Dowd, P.F., Mottiar, Y., Santoro, N., Karlen, S.D., Bukhman, Y.V., Thrower, N., Bruno, L.C., Moskvin, O.V., Johnson, E.T., Willhoit, M.E., Ralph, J., Mansfield, S.D., Nicholson, P., Sedbrook, J.C., Foster, C.E., Phutane, M. 2015. Effects of phenylalanine ammonia lyase (PAL) knockdown on cell wall composition, biomass digestibility, and biotic and abiotic stress responses in Brachypodium. Journal of Experimental Botany. DOI: 10.1093/jxb/erv269.
Interpretive Summary: Grasses underpin human civilization. Rice, maize, and wheat provide two-thirds of the global human food consumption and are staples for over four billion people (Food & Agriculture Organization of the United Nations, 2010). Grasses such as maize, oats, sorghum, tall fescue, and ryegrasses also provide feed for animals, whereas bluegrass, rye, and fescue (for example), provide groundcover for erosion control and landscaping. More recently, grasses have gained prominence as energy feedstocks. Sugars releasable from corn grain starch and inherent in sugarcane stem juices are routinely fermented to generate ethanol. Lignocellulosic biomass from grasses is an attractive alternative feedstock for liquid biofuels and electricity generation, given that species such as switchgrass and Miscanthus are highly productive on marginal lands, and residual biomass (stover) from cultivated crops such as maize and wheat is readily accessible. It is estimated that grasses could contribute more than half of the one billion dry tons of biomass envisioned for biofuels production in the U.S. each year.
Technical Abstract: Phenylalanine Ammonia Lyase (PAL) catalyzes the first step in the phenylpropanoid pathway in plants, controlling biosynthesis of a variety of structural and defense compounds including monolignols that polymerize into lignin. Gaps remain in our understanding of how genetic alterations to this pathway affect plant fitness in graminaceous species. To understand the nature and function of PAL genes, Brachypodium distachyon BdPAL RNA interference (RNAi) plants were generated and found to have large transcript level reductions (up to 85%) for two of the eight putative BdPAL genes. Plants from the strongest RNAi line exhibited a 43% reduction in Klason lignin content and a two-fold increase in the syringyl to guaiacyl (S:G) lignin units ratio, along with a 57% reduction in cell wall ester-linked ferulate moieties. BdPAL RNAi stem biomass released nearly twice as much polysaccharide-derived sugars upon acid or base pretreatment and hydrolytic enzymic partial digestion, compared to wild type (WT). Surprisingly, even though BdPAL RNAi plants had large reductions in lignin, they exhibited near-WT resistances to drought, ultraviolet light, and caterpillar herbivory. In contrast, BdPAL RNAi plants showed increased susceptibilities to the fungal pathogens Fusarium culmorum and Magnaporthe oryzae. Drug studies in combination with RNA-seq data suggest that the BdPAL RNAi plants’ reduced root growth and fungal susceptibility phenotypes were partially due to increased ethylene production and signaling. These data provide important insights into how Brachypodium, and likely other grasses, respond to and cope with challenges involving the phenylpropanoid pathway, providing targets for enhancing the fitness of economically important grasses.