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. 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).
Main collaboration: In France : C. Bruand, LIPM Toulouse; P. Mergaert, Gif-sur-Yvette; F. Frugier and V. Gruber, Saclay; or P. Kalo, SzentGyörgyi Albert u., Hungaria.
- Nodule senescence
- Cysteine proteases
- Regulation of gene expression
Current N-related Projects:
- ANR StayPINK : MECHANISMS CONTROLLING THE TRANSITION BETWEEN NITROGEN FIXATION AND SENESCENCE IN LEGUME SYMBIOTIC NODULES
El Msehli, S., Lambert, A., Hopkins, J., Boncompagni, E., Smiti-Aschi, S., Hérouart D. and Frendo P. (2018) Physiological and genetic changes during natural senescence of root nodules in Medicago truncatula. Journal of Plant Nutrition and Soil Science. Accepted.
YANG L., SYSKA C., GARCIA I., FRENDO P. and BONCOMPAGNI E. (2018). Involvement of proteases in nodule senescence in leguminous plants. John Wiley & Sons, Inc. The model legume Medicago truncatula. Ed.: Frans J. de Bruijn. Accepted.
HOPKINS J., PIERRE O., FRENDO P. and BONCOMPAGNI E. (2018) 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. Accepted.
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.