Skip to main content
ARS Home » Midwest Area » Madison, Wisconsin » U.S. Dairy Forage Research Center » Cell Wall Biology and Utilization Research » Research » Publications at this Location » Publication #405474
Research Project: Improving Utilization of Forages in Integrated Dairy Production Systems to Enhance Sustainable Farming Systems and Food Security

Location: Cell Wall Biology and Utilization Research

Title: Can we improve alfalfa cell wall digestibility by altering sugar-nucleotide interconversions?

Author
item Sullivan, Michael
item FANELLI, AMANDA - Oak Ridge Institute For Science And Education (ORISE)

Submitted to: Phytochemical Society of North America Meeting and Newsletter
Publication Type: Abstract Only
Publication Acceptance Date: 6/1/2023
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Alfalfa (Medicago sativa) is a forage crop widely used as a feed for ruminants. Although plant cell walls can be digested in the rumen to provide energy, cell walls of mature alfalfa stems (made up largely of cellulose, hemicellulose [mainly xylans], pectic polysaccharides, and lignin) are often poorly digested. Xylan interactions with cellulose and lignin contribute to the overall low digestibility. One approach to increase digestibility of alfalfa stem cell walls might be to reduce xylans while increasing cellulose and pectin. The building blocks that constitute cell wall polysaccharides are synthesized via sugar nucleotide interconversions. Xylose, the main monosaccharide in the xylan backbone, is formed through the decarboxylation of UDP-D-glucuronic acid (UDP-D-GlcA) by UDP-D-GlcA decarboxylase (UDP-D-xylose synthase [UXS]). In Arabidopsis, loss of function of cytosolic UXS impacts monosaccharide composition of the stem cell wall and digestibility. Might UXS downregulation in alfalfa lead to decreased xylan levels and improved cell wall digestibility while also increasing cellulose or pectin? To identify alfalfa UXS genes, we performed BLASTn searches of the alfalfa genome using Medicago truncatula UXS genes as query. The output genes were annotated and translated into proteins. A maximum likelihood phylogeny with the identified alfalfa UXS protein sequences, as well as those from M. truncatula and arabidopsis, was inferred using PhyML. In this tree, four alfalfa sequences were in the clade containing cytosolic UXS from arabidopsis. The identified genes correspond to two pairs of homologs, and each pair encodes a unique amino acid sequence. Analysis of published alfalfa RNAseq data show the four genes are more highly expressed in stems than leaves, consistent with a role in cell wall biosynthesis. To assess the role of these genes in planta, we have generated transgenic alfalfa with silencing or overexpression constructs. These will be analyzed for cell wall composition, structure, and digestibility.