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Title: Medicago truncatula as a Model for Dicot Cell Wall Development

Author
item TESFAYE, MESFIN - UNIVERSITY OF MINNESOTA
item Yang, Suk
item Lamb, Joann
item Jung, Hans Joachim
item Samac, Deborah - Debby
item Vance, Carroll
item Gronwald, John
item VANDENBOSCH, KATHRYN - UNIVERSITY OF MINNESOTA

Submitted to: BioEnergy Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/13/2009
Publication Date: 5/14/2009
Citation: Tesfaye, M., Yang, S.H., Lamb, J.F., Jung, H.G., Samac, D.A., Vance, C.P., Gronwald, J.W., Vandenbosch, K.A. 2009. Medicago truncatula as a Model for Dicot Cell Wall Development. BioEnergy Research. 2(1-2):59-76.

Interpretive Summary: The U.S. needs to reduce its dependency on foreign sources of energy. Developing cellulosic feedstocks to be used for ethanol production addresses this need. Alfalfa has considerable potential as a sustainable cellulosic feedstock. The model for the development of alfalfa as a bioenergy crop involves separating leaves from stems at harvest. The leaves would be used as a high-value livestock feed and the stems would be used for ethanol production. Developing new alfalfa varieties that have stems with high cellulose and low lignin will yield more ethanol and advance the development of alfalfa as a bioenergy crop. Key genes that regulate cellulose and lignin content of alfalfa stems need to be identified. However, identifying these genes in alfalfa is slow because this crop has a large, complex genome with few genomic resources. Barrel medic, a close relative of alfalfa, is considered to be a model plant for studying gene expression in alfalfa. Compared to alfalfa, barrel medic has a smaller genome and more genomic resources. Hence, studying gene expression in barrel medic may facilitate the identification of key genes regulating cellulose and lignin synthesis in alfalfa stems. To test this, we measured gene expression in stems of both barrel medic and alfalfa using the Medicago GeneChip. Similar patterns of gene expression were detected in both species, including several genes involved in cellulose and lignin synthesis. Studying gene expression in the model plant barrel medic will facilitate discovery of cellulose and lignin genes in alfalfa. The genes identified using this approach can be used as markers in a breeding program to develop new alfalfa varieties that yield more ethanol. The new knowledge discovered in this study advances the development of alfalfa as a bioenergy crop.

Technical Abstract: Strong interest in renewable energy has promoted an upsurge of research on plant cell wall traits that influence the availability of lignocellulosic-derived sugars for fermentation in production of biofuels. We have initiated a genome-wide transcript profiling study using the model legume Medicago truncatula to identify putative genes related to cell wall biosynthesis and regulatory function in legumes. We used the GeneChip Medicago Genome Array to compare transcript abundance in elongating versus post-elongation stem internode segments of two M. truncatula ecotypes and two M. sativa (alfalfa) clones with contrasting stem cell wall concentration and composition. Hundreds of differentially expressed probe sets between elongating and post-elongation stem segments showed similar patterns of gene expression in the model legume and cultivated alfalfa. Differentially expressed genes included genes with putative functions associated with primary and secondary cell wall biosynthesis and growth. Mining of public microarray data for genes co-expressed with two markers for secondary cell wall synthesis identified additional candidates for cell wall regulatory genes including protein kinases, transcription factors, and unclassified groups. Medicago truncatula has been recognized as an excellent model plant for legume genomics. The stem tissue transcriptome analysis described here indicates that M. truncatula has utility as a model plant for cell wall genomics in legumes in general and shows excellent potential for translating gene discoveries to its close relative, cultivated alfalfa, in particular. The natural variation for stem cell wall traits in Medicago may offer a new tool to study an expanded repertoire of valuable agronomic traits in related species including woody dicots in the eurosid I clade.