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Molecular analysis of nodule senescence and development of new cellular tools to analyze the symbiotic nitrogen fixing interaction in vivo.
In order to better understand the nitrogen fixing symbiosis, we have developed new cellular tools. In this context, multiple probes analyzed using confocal microscope imaging were developed and used in nitrogen fixing nodules. PBS pH was measured in vitro during the whole symbiotic process using ratiometric fluorescent probe. This analysis showed that nitrogen fixing zone maturation goes with the acidification of the peribacteroid space in the nitrogen-fixing organite, the symbiosome (Pierre et al., 2013). The viability of bacteroids was analyzed during their differentiation and throughout the symbiotic interaction in vivo using nodule sections with the Live/Dead® BacLightTM probe.
The symbiotic interaction between legumes and Rhizobiaceae leads to the formation of new root organs called nodules. Within the nodule, Rhizobiaceae differentiate into nitrogen-fixing bacteroids. However, this symbiotic interaction is time-limited as a result of the initiation of a senescence process, leading to a complete degradation of bacteroids and host plant cells. The increase in proteolytic activity is one of the key features of this process.
We analysed the involvement of two different classes of cysteine proteinases, MtCP6 and MtVPE, in the senescence process of Medicago truncatula nodules. Corresponding gene inductions were observed during both developmental and stress-induced nodule senescence (Kazmierczak et al., 2020; Yang et al., 2020). Both MtCP6 and MtVPE proteolytic activities were increased during stress-induced senescence. Down-regulation of both proteinases mediated by RNAi in the senescence zone delayed nodule senescence and increased nitrogen fixation, while their early expression promoted nodule senescence. Using green fluorescent protein fusions, in vivo confocal imaging showed that both proteinases accumulated in the vacuole of uninfected cells or the symbiosomes of infected cells. These data highlight the crucial role of MtCP6 and MtVPE in the onset of nodule senescence (Pierre et al., 2014; El Msehli et al., 2019).
In order to understand the regulation of MtCP6 expression in nodule undergoing a senescence program, a serial promoter deletion analysis of a cysteine protease gene MtCP6 wasconducted to identify cis regulatory element involved in the transcriptional regulation of nodule senescence of M. truncatula. Thereafter, identified cis-regulating region (67bp, NS) was validated to function in transcription activation in nodule zone III-IV. We have shown that tetramers of NS can increase the transcription into nodule senescence zone. In order to determine the significance of NS to the expression compared to the full promoter (-1,710bp), a functional analysis was conducted with deletion of NS from the full promoter and the analysis of a minimal promoter (-254bp). In addition, the potential roles of CAAT,WRKY and Dof motifs localized at 5’ of NS sequence was validated by site-specific mutagenesis. Finally, yeast one hybrid experiment was performed to identify transcription factors interacting with NS DNA fragment (Yang, 2020-PhD).
Main collaboration: In France : C. Bruand, LIPM Toulouse; P. Mergaert, ISV Gif-sur-Yvette; F. Frugier and V. Gruber, Gif-sur-Yvette; or P. Kalo, SzentGyörgyi Albert u., Hungaria. F. Di Carvalho-Niebel, LIPM Toulouse.
2016-2020 - Elected member at Research commission (CACR) at Nice Sophia Antipolis University.
2020-2024 - Elected member at Research commission (CACR) at Nice Côte d'azur University.
2020-2024 - Elected member at Disciplinary section
2018-2020 - Elected member at Epi-Revel editorial comity at Nice Côte d'azur University.
Financial support and collaborations :
ANR StayPink 2016-2020 (Saclay and Toulouse)
PHC 2014-2015 (Hungary)
CSI UNS 2018 (Toulouse)
December 2013, December 2016 and December 2019: 47h in Master 1 and 2, USTH Introduction to Plant Biotechnology, Hanoi, Vietnam.
Otherwises, 192 h/year at UNS. Courses on Plant Biology, Plant Physiology, Molecular Plant Biology, Microbiology.
Kazmierczak T.,Yang L., Boncompagni E., Meilhoc E., Frugier F., Frendo P., Bruand C., Gruber V. and Brouquisse R.(2020) Legume nodule senescence: a coordinated death mechanism between bacteria and plant cells. Advances in Botanical Research, 94, 181-212. DOI:10.1016/bs.abr.2019.09.013
Yang L., El Mselhi S., Benyamina S., Lambert A., Hopkins J., Cazareth J. Hérouart D., Smiti S.-A., Boncompagni E. and Frendo P. (2020). Glutathione Deficiency in Sinorhizobium meliloti Does Not Impair Bacteroid Differentiation But Induces Early Senescence. Frontiers in plant science. Accepted DOI: 10.3389/fpls.2020.00137
El Msehli S., Lambert A., Hopkins J., Boncompagni E., Smiti-Aschi S., Hérouart D. and Frendo P. (2019) Physiological and genetic changes during natural senescence of root nodules in Medicago truncatula. Journal of plant nutrition and soil science, 182(3), 385-392 https://doi.org/10.1002/jpln.201800233
Hopkins J., Pierre O., Frendo P. and Boncompagni E. (2019) FYVE and PH protein domains present in MtZR1, a PRAF protein, modulate the development of roots and symbiotic root nodules of Medicago truncatula via potential phospholipids signalling. John Wiley & Sons, Inc. The model legume Medicago truncatula. Ed.: Frans J. de Bruijn. https://doi.org/10.1002/9781119409144.ch17
Alloing, G.; Mandon, K.; Boncompagni, E.; Montrichard, F.; Frendo, P. (2018) Involvement of Glutaredoxin and Thioredoxin Systems in the Nitrogen-Fixing Symbiosis between Legumes and Rhizobia. Antioxidants, 7, 182. doi.org/10.3390/antiox7120182
BONCOMPAGNI E., ALLOING G., MANDON K. and FRENDO P. Synthesis and Roles of Glutathione and Homoglutathione in the Nitrogen-Fixing Symbiosis. Springer : Glutathione in plant growth, development and stress tolerance. Ed. : Mohammad Anwar Hossain, Mohammad Golam Mostofa, Pedro Diaz Vivancos, David J Burritt, Masayuki Fujita, and Lam-Son Phan Tran. Accepted.
Ribeiro CW, Baldacci-Cresp F, Pierre O, Larousse M, Benyamina S, Lambert A, Hopkins J, Castella C, Cazareth J, Alloing G, Boncompagni E, Couturier J, Mergaert P, Gamas P, Rouhier N, Montrichard F, Frendo P. (2017). Regulation of Differentiation of Nitrogen-Fixing Bacteria by Microsymbiont Targeting of Plant Thioredoxin s1. Curr Biol 27(2):250-256. doi : 10.1016/j.cub.2016.11.013.
Hopkins, J., Pierre, O., Kazmierczak, T., Gruber, V., Frugier, F., Clement, M., Frendo, P., Herouart, D., and Boncompagni, E. (2014). MtZr1, A Praf Protein, is Involved in the Development of Roots and Symbiotic Root-nodules in Medicago truncatula.Plant, Cell & Environment 37, 658-669 10.1111/pce.12185.
Pierre, O., Hopkins, J., Combier, M., Baldacci, F., Engler, G., Brouquisse, R., Hérouart, D., and Boncompagni, E. (2014). Involvement of papain and legumain proteinase in the senescence process of Medicago truncatula nodules. New Phytologist. 202(3):849-63. DOI: 10.1111/nph.12717.
Pierre, O., Engler, G., Hopkins, J., Brau, F., Boncompagni, E., and Hérouart, D. (2013). Peribacteriod space acidification: a marker of mature bacteroid functioning in Medicago truncatula nodules. Plant Cell Environ. 36(11):2059-70
Cam Y., Pierre O., Boncompagni E., Hérouart D., Meilhoc E. and Bruand C. (2012) Nitric oxide (NO): a key player in the senescence of Medicago truncatula root nodules. New Phytolologist, 196, 548–560.
El Msehli S., Lambert A., Baldacci-Cresp F., Hopkins J., Boncompagni E., Smiti S.A., Hérouart D. and Frendo P. (2011) Crucial role of (homo)glutathione for nitrogen fixation in Medicago truncatula nodule. New Phytologist, 192: 496-506.
Haag AF, Balodan M, Sani M, Kerscher B, Pierre O, Longhi R, Boncompagni E, Herouart D, Staff E, Dall’angelo S, Kondorosi E, Zanda M, Mergaert P, and Ferguson GP (2011) Bacterial resistance to legume defensin peptides is essential for symbiosis. Plos Biology, Oct. 9 (10):e1001169. DOI: 10.1371/journal.pbio.1001169.
Horchani F, Prévot M, Boscari A, Evangelisti E, Meilhoc E, Bruand C, Raymond P, Boncompagni E, Smiti S, Puppo A, Brouquisse R (2011) Both plant and bacterial nitrate reductases contribute to nitric oxide production in Medicago truncatula nitrogen-fixing nodules. Plant Physiology, 155: 1023-1036.
Fig 1: A- Nodulated Medicago truncatula plant; B- Slice of functional nodule. Scale: 500 µm; C- Activation of CP6 gene at the interface between symbiosis and senescence (Red = Gus detection); D- Bacteroid of S. meliloti (Syto® 9 fluorecence); E- Detection of low pH in peribacteroid space (green: LysoTracker®) and bacteroid (red:Syto® 9).
Fig 2: A- Nodule morphology (toluidine blue staining) of nodule depleted for CP6 or VPE genes. Scale: 250µm. B- Nitrogen fixation of 6 weeks post-inoculation MtCP6-RNAi and MtVPE-RNAi nodules (mean + SD). Differences are significant: *, P<0.05; **, P<0.01.