Lectin genes from the legume Medicago truncatula

We report the cloning and characterization of two lectin genes from Medicago truncatula, designated Mtlec1 and Mtlec2. The two genes show a high degree of homology and apparently belong to a small multigene family. Mtlec1 appears to encode a functional lectin with 277 amino acids, whereas Mtlec2 is probably non-functional, since a frameshift mutation (insertion of two nucleotides) leads to premature translation termination after only 98 amino acids. The deduced amino acid sequence of the polypeptide MtLEC1 suggests that this lectin is a metalloprotein with Glc/Man specificity.     

Epigenetic Regulation of a Powdery Mildew Resistance Gene in Medicago truncatula

Dear Editor, Medicago truncatula is a model legume that is conge- neric with alfalfa （Medicago sativa）, a forage crop of global importance. Over the last decade, tremendous genetic and genomic tools have been developed for this model system, which has greatly facilitated the study of various aspects of legume genomics and biology. From an applied perspective, genomic information gained from M. truncatula is particu- larly useful for genetic improvement of cultivated alfalfa, a crop that is not amenable to genetic analysis because of its allogamous and autotetraploid nature （Yang et al., 2008）. For instance, M. truncatula can be used to clone the orthologs of many economically important genes in alfalfa,     

Annotating the genome of Medicago truncatula

Medicago truncatula will be among the first plant species to benefit from the completion of a whole-genome sequencing project. For each of these species, Arabidopsis, rice and now poplar and Medicago, annotation, the process of identifying gene structures and defining their functions, is essential for the research community to benefit from the sequence data generated. Annotation of the Arabidopsis genome involved gene-by-gene curation of the entire genome, but the larger genomes of rice, Medicago and other species necessitate the automation of the annotation process. Profiting from the experience gained from previous whole-genome efforts, a uniform set of Medicago gene annotations has been generated by coordinated international effort and, along with other views of the genome data, has been provided to the research community at several websites.     

Crystal structures of a multifunctional triterpene/flavonoid glycosyltransferase from Medicago truncatula

Glycosylation is a ubiquitous reaction controlling the bioactivity and storage of plant natural products. Glycosylation of small molecules is catalyzed by a superfamily of glycosyltransferases (GTs) in most plant species studied to date. We present crystal structures of the UDP flavonoid/triterpene GT UGT71G1 from Medicago truncatula bound to UDP or UDP-glucose. The structures reveal the key residues involved in the recognition of donor substrate and, by comparison with other GT structures, suggest His-22 as the catalytic base and Asp-121 as a key residue that may assist deprotonation of the acceptor by forming an electron transfer chain with the catalytic base. Mutagenesis confirmed the roles of these key residues in donor substrate binding and enzyme activity. Our results provide an initial structural basis for understanding the complex substrate specificity and regiospecificity underlying the glycosylation of plant natural products and other small molecules. This information will direct future attempts to engineer bioactive compounds in crop plants to improve plant, animal, and human health and to facilitate the rational design of GTs to improve the storage and stability of novel engineered bioactive compounds.     

Regeneration of Medicago truncatula from protoplasts isolated from kanamycin-sensitive and kanamycin-resistant plants

Medicago truncatula (barrel medic) is an annual legume of agricultural and biological interest. In this report regeneration from isolated mesophyll protoplasts is described. A specifically developed, highly regenerable seed line is essential for regeneration. Other critical requirements for regeneration are the starting plant material, the use of agarose droplets incubated in a shallow layer of liquid medium, and protoplast density. Plants are grown in controlled environment conditions. Protoplasts are purified using a Percoll-based flotation procedure, then embedded in 100 l agarose droplets containing a basal medium plus 25 M NAA and 4 M BAP (the same medium as in the surrounding shallow liquid layer) to induce protoplast division. A protoplast density of 6–8×10⁵ ml^–1 is required for maximum colony formation. M. truncatula plants previously transformed for kanamycin resistance yielded embryogenic callus and also regenerated plants. Protoplasts from other annual Medicago (M.intertexta and M.scutellata) species readily form calli by the procedure we have described.Abbreviations BAP 6-benzylaminopurine - 2,4-D 2,4-dichlorophenoxyacetic acid - NAA 1-naphthaleneacetic acid     

Characterization of pea aphid resistance in Medicago truncatula

To achieve a thorough understanding of plant-aphid interactions, it is necessary to investigate in detail both the plant and insect side of the interaction. The pea aphid (PA; Acyrthosiphon pisum) has been selected by an international consortium as the model species for genetics and genomics studies, and the model legume Medicago truncatula is a host of this aphid. In this study, we identified resistance to PA in a M. truncatula line, 'Jester', with well-characterized resistance to a closely related aphid, the bluegreen aphid (BGA; Acyrthosiphon kondoi). The biology of resistance to the two aphid species shared similarity, with resistance in both cases occurring at the level of the phloem, requiring an intact plant and involving a combination of antixenosis, antibiosis, and plant tolerance. In addition, PA resistance cosegregated in 'Jester' with a single dominant gene for BGA resistance. These results raised the possibility that both resistances may be mediated by the same mechanism. This was not supported by the results of gene induction studies, and resistance induced by BGA had no effect on PA feeding. Moreover, different genetic backgrounds containing a BGA resistance gene from the same resistance donor differ in resistance to PA. These results suggest that distinct mechanisms are involved in resistance to these two aphid species. Resistance to PA and BGA in the same genetic background in M. truncatula makes this plant an attractive model for the study of both plant and aphid components of resistant and susceptible plant-aphid interactions.     

蒺藜苜蓿多聚半乳糖醛酸酶基因家族的全基因组分析

多聚半乳糖醛酸酶(Polygalacturonases,PGs)是一种果胶水解酶,参与果实成熟、器官脱落、花粉成熟等多个植物发育过程。采用相似性比对和结构域搜索方法,从蒺藜苜蓿基因组中共鉴定出74个MtPG基因。根据系统进化关系将其分为6个亚家族,分别包含9、7、4、11,18和25个MtPG基因家族成员。染色体定位分析发现,MtPG基因在蒺藜苜蓿的8条染色体上呈现不均匀分布,每条染色体上分布有2-16个MtPG基因;同时,基因组复制分析结果显示,蒺藜苜蓿的PG基因家族成员之间存在大量的基因复制。最后,通过蒺藜苜蓿的高通量测序数据分析发现,MtPG基因家族广泛地在根部、结瘤、叶片、芽,心皮和花等组织中表达。根据它们在不同组织中表达水平,将31个MtPG基因聚类为4组,分别探讨了四组基因在蒺藜苜蓿组织器官分化中表达模式,重点解析了它们在花器官发育以及根部组织分化中可能的调控机制,这将为进一步研究蒺藜苜蓿MtPG基因家族成员的基因功能提供了理论基础。     

Microtubule dynamics in root hairs of Medicago truncatula

The microtubular cytoskeleton plays an important role in the development of tip-growing plant cells, but knowledge about its dynamics is incomplete. In this study, root hairs of the legume Medicago truncatula have been chosen for a detailed analysis of microtubular cytoskeleton dynamics using GFP-MBD and EB1-YFP as markers and 4D imaging. The microtubular cytoskeleton appears mainly to be composed of bundles which form tracks along which new microtubules polymerise. Polymerisation rates of microtubules are highest in the tip of growing root hairs. Treatment of root hairs with Nod factor and latrunculin B result in a twofold decrease in polymerisation rate. Nonetheless, no direct, physical interaction between the actin filament cytoskeleton and microtubules could be observed. A new picture of how the plant cytoskeleton is organised in apically growing root hairs emerges from these observations, revealing similarities with the organisation in other, non-plant, tip-growing cells.     

Differential regulation of a family of apyrase genes from Medicago truncatula

Four putative apyrase genes were identified from the model legume Medicago truncatula. Two of the genes identified from M. truncatula (Mtapy1 and Mtapy4) are expressed in roots and are inducible within 3 h after inoculation with Sinorhizobium meliloti. The level of mRNA expression of the other two putative apyrases, Mtapy2 and Mtapy3, was unaffected by rhizobial inoculation. Screening of a bacterial artificial chromosome library of M. truncatula genomic DNA showed that Mtapy1, Mtapy3, and Mtapy4 are present on a single bacterial artificial chromosome clone. This apyrase cluster was mapped to linkage group seven. A syntenic region on soybean linkage group J was found to contain at least two apyrase genes. Screening of nodulation deficient mutants of M. truncatula revealed that two such mutants do not express apyrases to any detectable level. The data suggest a role for apyrases early in the nodulation response before the involvement of root cortical cell division leading to the nodule structure.