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
Endosymbionts of legumes belonging to Inverted Repeat-Lacking Clade (IRLC) undergo dramatic changes including cell elongation, genome endoreduplication, alteration of membrane permeability and loss of reproductive capacity. This terminal bacteroid differentiation is driven by the host via nodule-specific cysteine-rich peptides (NCRs). The NCR gene family codes for about 600 highly divergent secreted peptides in M. truncatula. Identification of bacterial targets of host peptides is currently the main challenge that can shed light on the mode of the peptides' action that leads to the altered physiology of bacteria and evolutionary success of terminal endosymbiont differentiation in Rhizobium-legume symbiosis.
BACKGROUND
Leguminous plants establish symbiosis with nitrogen fixing soil bacteria known as rhizobia. Symbiotic nitrogen fixation takes place in specialized root organs called nodules. Endosymbionts of most legumes in the Inverted Repeat-Lacking Clade (IRLC) undergo striking modifications (cell enlargement, altered morphology, genome endoreduplication, increased membrane permeability and loss of reproductive capacity). This terminal differentiation of bacteroids is regulated by the host via nodule-specific cysteine-rich peptides (NCRs). The NCR gene family codes for about 600 highly divergent secreted peptides in M. truncatula and its members are expressed exclusively in Rhizobium-infected nodule cells. Different subsets of NCRs are produced during each steps of the nodule development. The NCR genes are scattered on the eight chromosomes of M. truncatula but often they are clustered. The NCR genes are small and usually consist of two exons: the first one codes for a relatively conserved signal peptide while the second one for the mature, usually 30-50 amino acid long active peptide. The NCR peptides are highly divergent but all of them contain 4 or 6 cysteines in conserved positions. The bacterial targets of NCR peptides are mostly unknown, however, based on the localization of the peptides, they can be found in the membrane or in the cytosol of the bacteria and might be proteins, nucleic acids or lipids.
CURRENT RESEARCH
The extraordinarily high number of NCR peptides raises the question why M. truncatula uses such a large arsenal of nodule-specific peptides to control the bacteroid differentiation. Generally, in nature, one or only a few proteins is/are dedicated for a given biochemical function. In large protein families individual members can have unique specificities. Thus, it is likely that the NCR family is not required for a single function, but rather it provides multiple activities during bacteroid differentiation. It is possible that distinct sets of peptides act in a concerted manner at the different stages. It is likely that of the 600 NCR peptides many would have redundant functions, however, we cannot exclude the possibility that master NCRs might exist whose function is unique and cannot be substituted by any of the other 600 peptides. Little is known about the function and exact mode of action of NCRs. Cationic NCRs can interact with bacterial membranes, increase the membrane permeability and they possess de facto antimicrobial activities in vitro. Recently we published that NCR247 has multiple bacterial targets affecting bacterial gene expression, translation and metabolism and causing arrest of endosymbionts’ cell division.
SPECIFIC AIMS
Genetic approach is useful tool to dissect the molecular function of individual NCR peptides. Detailed study of nodule and bacteroid development of knock out or knock down M. truncatula mutants (in which NCRs are affected) can reveal how these peptide exert their effects. Moreover, the effects of production of recombinant, tagged NCR peptide in E. coli expression system and in transgenic plants along with identification of potential interacting partners of selected NCRs (using pull down or immunoprecipitation techniques) will help us to elucidate the role of particular NCR peptides during bacteroid development and in symbiotic nitrogen fixation.
METHODS TO BE LEARNED/APPLIED
• molecular cloning (generation of gene constructs for production of tagged NCRs in E. coli expression system and/or in planta)
• recombinant protein production and purification, identification of putative interacting proteins by pull down and immunoprecipitation
• testing gene constructs in nodulation test
• confocal microscopy (monitoring the nodule and bacteroid development of mutant plants)
SUGGESTED READINGS
Farkas A, et al.: Medicago truncatula symbiotic peptide NCR247 contributes to bacteroid differentiation through multiple mechanisms. Proc. Natl. Acad. Sci. USA, 111: 5183–5188 (2014)
Kereszt A, et al.: Bacteroid development in legume nodules: evolution of mutual benefit or of sacrificial victims? Mol. Plant-Microbe Int., 24:1300-1309.
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)
Penterman J, et al.: Host plant peptides elicit a transcriptional response to control the Sinorhizobium meliloti cell cycle during symbiosis. Proc. Natl. Acad. Sci. USA, 111:3561-3566
Van de Velde W, et al.: Plant peptides govern terminal differentiation of bacteria in symbiosis. Science, 327:1122-1126 (2010)
előírt nyelvtudás: angol felvehető hallgatók száma: 1
Jelentkezési határidő: 2017-01-31
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).
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