A nonRD receptor-like kinase prevents nodule early senescence and defense-like reactions during symbiosis

Fathi Berrabah , Marie Bourcy (1) , Alexis Eschstruth (2) , Anne Cayrel (2) , Ibtissem Guefrachi , Peter Mergaert (2) , Jiangqi Wen , Viviane Jean (3) , Kirankumar Mysore , Benjamin Gourion (4) , Pascal Ratet (2)

1 IRHS - Institut de Recherche en Horticulture et Semences
2 ISV - Institut des sciences du végétal
3 LGDP - Laboratoire Génome et développement des plantes
4 UMR LSTM - Laboratoire des symbioses tropicales et méditerranéennes

Rhizobia and legumes establish symbiotic interactions leading to the production of root nodules, in which bacteria fix atmospheric nitrogen for the plant's benefit. This symbiosis is efficient because of the high rhizobia population within nodules. Here, we investigated how legumes accommodate such bacterial colonization. We used a reverse genetic approach to identify a Medicago truncatula gene, SymCRK, which encodes a cysteine-rich receptor-like kinase that is required for rhizobia maintenance within the plant cells, and performed detailed phenotypic analyses of the corresponding mutant. The Medicago truncatula symCRK mutant developed nonfunctional and necrotic nodules. A nonarginine asparate (nonRD) motif, typical of receptors involved in innate immunity, is present in the SymCRK kinase domain. Similar to the dnf2 mutant, bacteroid differentiation defect, defense-like reactions and early senescence were observed in the symCRK nodules. However, the dnf2 and symCRK nodules differ by their degree of colonization, which is higher in symCRK. Furthermore, in contrast to dnf2, symCRK is not a conditional mutant. These results suggest that in M. truncatula at least two genes are involved in the symbiotic control of immunity. Furthermore, phenotype differences between the two mutants suggest that two distinct molecular mechanisms control suppression of plant immunity during nodulation.

Mots clés: chronic infection; defense reactions; endosymbiosis; rhizobium; intracellular infection; nitrogen fixation; nodulation

Domaines: Sciences du Vivant [q-bio]; Biologie végétale

Fathi Berrabah, Marie Bourcy, Alexis Eschstruth, Anne Cayrel, Ibtissem Guefrachi, et al.. A nonRD receptor-like kinase prevents nodule early senescence and defense-like reactions during symbiosis. New Phytologist, 2014, 203 (4), pp.1305-1314. ⟨10.1111/nph.12881⟩. ⟨hal-02410361⟩