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Home | Seminars and Symposia | Past seminars/symposia: Friday, September 15, 2006

Sequencing the genome of the model legume plant, Medicago truncatula


Nevin Young
Plant Pathology

Friday, September 15, 2006
12:00 Lunch
12:15 Seminar

402 Walter Library

Download slides (pdf 1.15 MB) Medicago truncatula is a model legume that is now being sequenced by an international consortium using a clone-by-clone sequencing strategy. Medicago was chosen because it was already a model for symbiosis research and it possesses a small genome size of ~500 million base pairs (Mbp). Previous research demonstrated that nearly all Medicago genes reside in the chromosome arms, distinctly separate from condensed regions located around centromeres. Sequencing in Medicago is “BAC-by-BAC” so the result will be a high quality sequence spanning entire chromosome arms with minimal gaps that is immediately useful for comparative genomics. Based on projections from expressed sequence tag (EST)-coverage, the euchromatin (“gene-space”) of Medicago is 280 Mbp, with ~70% complete as of September 2006. Automated annotation, based on a pipeline of intrinsic and extrinsic gene-finding algorithms, is taking place throughout the sequencing effort. Gene density is reasonably high, approximately one gene every 5 kilobase pairs (kb) and one exon every 1.4 kb. Medicago displays extensive synteny (conservation in gene content and order) with other plants, including soybean and Arabidopsis thaliana, at both macro- and micro-syntenic levels. Unlike most other plants examined to date, there is no evidence of lineage-specific genome duplication within Medicago, but instead, one very early in the evolution of legumes. Interesting Medicago-specific repeats are diagnostic for regions surrounding pericentromeres and for specific chromosomes, while large gene families show distinctive and informative distribution patterns. Medicago’s desirable features as a model legume combined with a comprehensive, high quality genome sequence will enable faster gene discovery in crops, insights into developmental and biochemical networks, and better understanding about the evolution of plants.