Research - Institute of Genetics - Plant and Microbial Genetics Unit - Medicago Genetics Group

Gabriella ENDRE
senior research associate

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Szilárd KOVÁCS Ph.D. student
Sándor JENEI engineer
Zsuzsanna LIPTAY laboratory assistant

MEDICAGO GENETICS GROUP

The main research efforts of the Medicago Genetics Group in the Institute of Genetics target the molecular processes leading to the formation of symbiotic nitrogen fixation as well as the plant genes governing this development. The group studies not only the genes responsible for the early signaling events necessary for the symbiotic nodule establishment but also their protein products and performs comparative analyses at the evolutionary level. During their work, they apply classical plant genetics along with the up-to-date tools of genomics and bioinformatics and the wide range of techniques of molecular biology. Establishing an efficient nitrogen fixing symbiosis also requires turning off and specific reprogramming of the plant immune system. Therefore, recent experiments aim to recognize molecules playing key roles in this course of events.


Molecular background of the nitrogen fixing symbiosis

Legumes have been known to form nodules on their roots - in which bacteria live and can fix nitrogen and pass it on to the plant - for a long time. Not only are the nitrogen requirements of the symbiotic plant partner fulfilled this way, but the soil becomes rich in nitrogen-containing compounds as well. The positive impact of this very efficient biological nitrogen fixation has been used in crop rotations for several hundreds of years; nevertheless, the molecular background of the process has only been examined since a few decades. The investigation of the bacterial molecules and genes needed for the development and function of this symbiosis started in the early seventies (including our institute) while studies on the plant genes became achievable due to technical advances about 20 years later. As a result of all these efforts, we already have important knowledge about the processes taking place during the formation of symbiotic nodules, about the signal molecules needed from the bacteria and the plants, and about the genetic determinants controlling them. A dialogue can be discovered in which the two symbiotic partners identify each other with high confidence in several steps and guarantee the processes that lead to the complete development and function of the nitrogen fixing nodules. In addition, ongoing genome programs help us learn about and analyze the homologous counterparts of the plant genes specialized in this symbiosis in plant species within and outside of legumes.

During the establishment of nitrogen fixing symbiosis, a novel plant organ, the root nodule, develops in which endosymbiont rhizobia reduce atmospheric nitrogen and deliver it to the plant for utilization. The initiation of the nodule growth needs Rhizobium strains specific to the given legume plant host, and its progress requires further signal exchanges between the partners. By positional cloning, we have isolated the first plant gene encoding for a receptor kinase which is indispensable for the nodulation. Several other symbiotic plant genes have been identified since then in our lab and all over the world; their analysis is in process. In a novel project, we also investigate how the plant immune system is influenced by the microsymbionts tuning it for the symbiosis. The genes and gene products playing an important role in the determination of the actual type of plant-microbe interaction are searched for. Comprehensive studies on these plant genes and their protein products will provide us more important information about the molecular bases of nitrogen fixing symbiosis. Rational utilization of the knowledge acquired by these scientific experiments may enable the establishment of more efficient nitrogen fixation and its expansion in the plant world.



Confocal microscopic picture of a symbiotic nodule.


Medicago genomics

Several different legume plants have been the subjects of biological studies for a long time: e.g., pea, soybean, or alfalfa, primarily due to their agronomic importance. Model organisms proved to be useful to answer biological questions that are more difficult to study directly in cultivated and often genetically recalcitrant species because of their disadvantageous characteristics such as large genome, long life-cycle, and lack of techniques for genetic manipulation. In recent years, Medicago truncatula has been recognized as an excellent legume model in view of its advantageous characteristics (small, diploid genome, self-fertility, and short life cycle). Its genome sequence has been published, and various genetic and genomic tools have been developed. Alongside the experiments using large-scale techniques, the functional analysis of selected genes and their products continues in order to clarify their role in plant development and interactions. One very useful tool in these approaches is the creation and utilization of mutant plant populations. An EU FP6 Grain Legumes Integrated Project with a large-scale mutagenesis program has contributed a great number of mutants for M. truncatula studies. We participated in the study and are currently holding a part of the seed collection of the insertional mutant lines. This collection is now being further developed within the frame of a bilateral French-Hungarian project and is used for studying symbiotic and root developmental genes.

Large-scale FST sequencing is used for the identification of the genes carrying insertions in the mutant lines. These data are integrated with data from phenotypic screens, as well as with other sequence-related information available in the databases, i.e., transcriptional data. Since the model legume, M. truncatula, is a close relative of several plants cultivated in Europe (alfalfa, pea, clovers), and comparative genomic studies suggest good synteny with these species, we expect to be able to use the results obtained on the model plant also in the improvement of the cultivated legume species.

Selected publications

Kiss E, Muñoz A, Oláh B, Kaló P, Morales M, Heckmann AB, Borbola A, Lózsa A, Kontár K, Middleton P, Downie JA, Oldroyd GED, Endre G (2009) LIN, a novel type of U-box/WD40 protein, controls early infection by rhizobia in legumes. Submitted

Tadege M, Wen J, He J, Tu H, Kwak Y, Eschstruth A, Cayrel A, Endre G, Zhao PX, Chabaud M, Ratet P, and Mysore KS (2008) Large scale insertional mutagenesis using Tnt1 retrotransposon in the model legume Medicago truncatula. Plant J. 54: 335-347

Kevei Z, Lougnon G, Mergaert P, Horváth GV, Kereszt A, Jayaraman D, Zaman N, Marcel F, Regulski K, Kiss GB, Kondorosi A, Endre G, Kondorosi E and Ané J-M (2007) A 3-Hydroxy-3-Methylglutaryl Coenzyme A Reductase Interacts with NORK in the Nodulation Signaling Pathway. Plant Cell 19: 3974-89

Mun JH, Kim DJ, Choi HK, Gish J, Debelle F, Mudge J, Denny R, Endre G, Saurat O, Dudez AM, Kiss GB, Roe B, Young ND, Cook DR (2006) Distribution of microsatellites in the genome of Medicago truncatula: A resource of genetic markers that integrate genetic and physical maps. Genetics 172: 2541-2555

Kevei Z, Seres A, Kereszt A, Kaló P, Kiss P, Tóth G, Endre G, Kiss GB (2005) Significant microsynteny with new evolutionary highlights is detected between Arabidopsis and legume model plants despite the lack of macrosynteny. Mol. Gen. Genomics 274: 644-657

Kuppusamy KT, Endre G, Prabhu R, Penmetsa RV, Veereshlingam H, Cook DR, Dickstein R, VandenBosch KA (2004) LIN, a Medicago truncatula gene required for nodule differentiation and persistence of rhizobial infections. Plant Physiol. 136: 3682–3691

Liu J, Blaylock LA, Endre G, Cho J, Town CD, VandenBosch KA,. Harrison MJ (2003) Transcript profiling coupled with spatial expression analyses reveals genes involved in distinct developmental stages of the arbuscular mycorrhizal symbiosis. Plant Cell 15: 2106-2123

Endre G, Kereszt A, Kevei Z, Mihacea S, Kaló P, Kiss GB (2002) A receptor kinase gene regulating symbiotic nodule development Nature 417: 962-966

Endre G, Kaló P, Kevei Z, Kiss P, Mihacea S, Szakál B, Kereszt A, Kiss GB (2002) Genetic mapping of the non-nodulation phenotype of the mutant MN-1008 in tetraploid alfalfa (Medicago sativa) Mol. Gen. Genomics 266: 1012-1019

Kaló P, Endre G, Zimányi L, Csanádi G, Kiss GB (2000) Construction of an improved linkage map of diploid alfalfa (Medicago sativa) Theor. Appl. Genet. 100: 641-657