Alfalfa-Sinorizobium rhizospheric communication in adverse thermal conditions

NATALIA SOLEDAD PAULUCCI; CESARI A. B; NUEVA MURATORE L; CASTILLA MARIN V

Lisboa

Congreso; XVIII Congress on benefical Plant-microbe interactions; 2022

Sociedad Española de Fijación del Nitrógeno (SEFIN)

Root hairs exudate compounds that act as a chemotactic signal or promote the growth of symbiotic fungi andbacteria. Moreover, they are directly involved in the formation of nitrogen-fixing nodules in legumes, secretessignaling flavonoid compounds that are perceived by the rhizobial symbiont, which responds to this message bysecreting specific lipochitooligosaccharides, named Nod factors (NF). NF are signal molecules whose binding toroot hair receptors triggers complex signaling events leading the root hair to curl and thereby to entrap rhizobia.Then, an infection thread develops, allowing rhizobia to migrate through the root cortex toward the noduleprimordium. In alfalfa, they elicit root-hair deformation, cortical cell divisions and the formation of genuinenodules. The synthesis and secretion of flavonoids and NF by different legume–rhizobia interactions were foundto be altered under environmental stress conditions (Guasch-Vidal et al., 2013). Among environmental factors,temperature is the one exerting the strongest impact on the cell envelope of S. meliloti, modifying its lipidcomposition and its biophysical state, which can affect the establishment of the symbiosis with alfalfa (Paulucci, etal., 2021). Although the effect of NF secreted by S. meliloti under optimal conditions on early interaction eventswith alfalfa roots is known (Damiani et al., 2016), there is a lack of information on what could be caused by thoseNF secreted under non-optimal conditions, such as temperature. For this reason, the objective of this work was toevaluate the effect of the FN produced by S. meliloti induced with luteolin at different stages of the thermal cycle(28°C-10°CInitial-.40°C-10°CFinal) on the curvature of alfalfa root hairs.We observed a higher number of root hair curvature events (distortion, shepherd´s crook and tip bending) inalfalfa roots inoculated with FN obtained from cultures of S. meliloti induced with luteolin after exposure to 40°C.This result is in agreement with that obtained in alfalfa inoculation tests with S. meliloti previously exposed to40°C. There we were able to observe a greater number of average nodules per plant (40±9) compared to theother conditions (24±9 and for 23±2 for 28°C and 10°CInitial respectively and 18±6 for 10°CFinal). In addition,when the roots were inoculated with FN secreted by S. meliloti in the 10°CFinal condition, root hair curvaturestructures different from the typical ones were observed.These results suggest that the FN produced by S. meliloti in the heating stage of the applied thermal cycle couldimprove the early molecular dialogue with alfalfa and the establishment of the symbiosis. Future studies of ourworking group are focused on elucidating the composition of the FN in this thermal condition.