témavezető: Kereszt Attila
helyszín (magyar oldal): Biological Reseach Centre HAS, Institute of Biochemistry, Symbiosis and Functional Genomics Unit, Laboratory of Plant Genomics helyszín rövidítés: SzBK
A kutatási téma leírása:
PROJECT SUMMARY
The symbiosis between rhizobia and legume plants is considered to be a mutualistic interaction, however, more and more evidence has appeared that the symbiotic partners has constantly evolved mechanism to maximize their own benefit from the partnership. For example, in the Medicago truncatula - Sinorhizobium meliloti symbiosis, the plant produces a plethora of small peptides in the cells invaded by its partner to direct the terminal differentiation of the bacteria resulting in higher nitrogen-fixation efficiency. On the other hand, bacteria evolve accessory functions which increase their ability to cheat the plants and/or to form a larger population of undifferentiated cells within the symbiotic organ that will be released into the environment after the symbiosis ceases to function. In most cases, these genes do not significantly inhibit nitrogen fixation, however, they may cause symbiotic incompatibility in interactions with a partner which carries a certain gene or gene variant. Bacterial and plant genes, gene variants causing symbiotic incompatibility will be identified.
BACKGROUND
The Fabaceae family comprising over 18000 species is the third largest family of flowering plants and constitutes approximately 27% of the world´s crop production. Their economic and ecologic importance is founded on the ability to establish a mutualistic association with α- and β-Proteobacteria commonly known as rhizobia. This symbiotic relationship provides reduced nitrogen to the host while the microsymbiont receives carbon sources in exchange as well as a niche to multiply. The mutualistic association takes place in the rhizosphere where after a molecular dialogue the bacteria attach to the root hairs and eventually are internalized through a tubular structure called the infection thread. Simultaneously, a primordium is established by the reactivation of cellular division in the cortex that leads to the formation of a novel organ, the root nodule. Subsequently the infection thread reaches the nodule primordia and the bacteria are released into the plant cells where they are encapsulated in membranes of plant origin and form organelle-like structures called symbiosomes. Within the symbiosomes the rhizobia differentiate into bacteroids and express the set of enzymes necessary to catalyze the conversion of atmospheric nitrogen into ammonia. The efficiency of this partnership is compromised when incompatible but otherwise (i.e. with other partners) effective symbionts establish the interaction. The understanding of gene-for-gene interaction in symbiosis may shed light on the arm-race of the symbiotic partners to maximize the benefits from the partnership.
CURRENT RESEARCH
To study gene-for-gene interactions in symbiotic settings, we employ the model system based on the Medicago truncatula -Sinorhizobium meliloti symbiosis. The symbiotic efficiency of a number of plant ecotypes collected from all around the Mediterranean basin with bacterial strains isolated in different continents has been tested under sterile conditions and incompatible interactions have been identified. We characterize an incompatible interaction first with microscopic analysis of the nodules formed after inoculating the plants with bacteria carrying reporter genes driven by constitutive or symbiosis specific promoters to determine at which step of the symbiotic nodule development is arrested. Then transcriptome analysis of both the bacterial and plant genomes are performed and gene expression changes are compared to those observed in effective interactions of the partners in order to identify those genes that are not repressed or induced during nodule development. This comparative analysis might reveal the pathways that are affected by the incompatibility and might indicate the function of genes responsible for the trait. Finally, we isolate and characterize the genes that cause the inefficiency of the partnership.
SPECIFIC AIMS
Phenotypic characterization and comparison of the compatible and incompatible interactions of the symbiotic partners with the help of light, confocal and electron microscopy using bacteria carrying reporter genes driven by constitutive or symbiosis specific promoters.
Obtaining the genome-wide gene expression profile of the symbionts with the help of RNA sequencing and comparing the profiles of the compatible and incompatible interactions .
Isolation of the bacterial gene responsible for the incompatible interaction via whole genome mutagenesis and/or complementation experiments.
Identification of the plant gene/allele that render the interaction with the specific partner incompatible with the help of map-based cloning.
METHODS TO BE LEARNED/APPLIED
• molecular cloning (generation of constructs for expresing genes in S. meliloti and in M. truncatula)
• genetic engineering of rhizobia
• plant transformation
• genetic mapping
• gene expression analysis (RNA-Seq, qRT-PCR)
• light and confocal microscopy (monitoring the nodule and bacteroid development of plants)
SUGGESTED READINGS
Kereszt A et al.: Bacteroid development in legume nodules: evolution of mutual benefit or of sacrificial victims? Mol Plant-Microbe Int 24:1300-1309 (2011).
Kondorosi E et al.: A paradigm for endosymbiotic life: cell differentiation of rhizobium bacteria provoked by host plant factors. Ann Rev Microbiol 67: 611-628 (2013)
Tirichine L et al.: Mtsym6, a Gene Conditioning Sinorhizobium Strain-Specific Nitrogen Fixation in Medicago truncatula. Plant Physiol 123: 845–851 (2000).
Crook MB et al.: Rhizobial plasmids that cause impaired symbiotic nitrogen fixation and enhanced host invasion. Mol Plant Microbe Interact 25: 1026-1033 (2012).
előírt nyelvtudás: angol ajánlott nyelvtudás (magyar oldal): angol felvehető hallgatók száma: 1
Jelentkezési határidő: 2018-02-28
2024. IV. 17. ODT ülés Az ODT következő ülésére 2024. június 14-én, pénteken 10.00 órakor kerül sor a Semmelweis Egyetem Szenátusi termében (Bp. Üllői út 26. I. emelet).
Bejelentkezés
