= Medicago truncatula
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<Medicago truncatula> is a <legume> widely used as a <model organism> for <plant> biology, particularly the association between <rhizobia> and <root nodules>. In this <symbiosis>, bacterial <nitrogen fixation> supplies biologically usable nitrogen within specialized plant structures. The <plant> and its microbial partners contribute different parts of the process.<The Medicago genome provides insight into the evolution of rhizobial symbioses by Nevin D. Young and others>[Abstract, model organism and nodule symbiosis]{ref}
The 2011 draft <genome> study combined a large-insert assembly with additional short-read sequence data. Comparing duplicated genomic regions and <genes> with enhanced activity in <root nodules> helped investigate how <gene duplication> contributed to the evolution of this <symbiosis>.<The Medicago genome provides insight into the evolution of rhizobial symbioses by Nevin D. Young and others>[Abstract and Figures 1–3, genome comparison and nodule-enhanced gene pairs]{ref} A useful comparison asks whether both copies of a duplicated <gene> retain nodule-associated activity or whether their expression patterns differ. Sequence similarity identifies candidate relatives; measuring activity supplies another kind of evidence about their roles.
The same <plant> also supports questions outside nodule formation. In a 2005 study, <fluorescence microscopy> of <green fluorescent protein>-labelled <Methylorubrum extorquens> derivatives located bacterial <cells> on leaves and in some internal spaces.<Methylotrophic metabolism is advantageous for Methylobacterium extorquens during colonization of Medicago truncatula under competitive conditions by Abdoulaye Sy and others>[Figure 5, confocal images and localization]{ref} This visualizes colonization. A fluorescent bacterium on a leaf does not by itself establish <nitrogen fixation>, nodule formation or a benefit to the host.
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