Oximes and nitric oxide signalling in Medicago truncatula root system architecture

Laburpena

Nitric oxide (NO) is a widely recognized signalling molecule in plants. It affects almost every developmental step during the whole plant’s lifespan. Among all of its already described functions, NO is recognised to act synergistically with Indole-3-acetic acid (IAA), promoting the development of the secondary roots. Until now, only a few reductive NO synthesis pathways have been confirmed, whereas no oxidative pathway has been yet described. Experiments of our research group measured de novo synthesis of NO3- and NO2- in Pisum sativum and M. truncatula grown with NH4+ as the sole N source (unpublished data). This fact suggests the existence of an oxidative pathway for NH4+ in the Fabaceae family, which is proposed to be part of the signalling of the NH4+ toxicity and to participate in the alleviation mechanism. Due to their molecular configuration, oximes are very strong candidates for being the precursors of NO, and thus the first step into this nitrogen oxidation pathway. Among these oximes, Indole-3-acetaldoxime (IAOx) is particularly relevant since it is placed in the crossroad between IAA and indole glucosinolates. The role of IAOx in growth-signalling and root phenotype is poorly studied in cruciferous plants and mostly unknown in non-cruciferous plants. In this PhD thesis, we aim to demonstrate that IAOx is present in M. truncatula playing an important role of signalling during plant root development and also that this signalling is mediated by NO. For that purpose, we synthesized a set of pure IAOx and other indolic and non-indolic oximes and performed pharmacological approaches with the model legume M. truncatula. We analysed the root phenotype, quantified the indolic compounds in tissue (shoots and roots) and measured the Indole-3- acetaldehyde oxidase and IAOx dehydratase genes expression. Our data showed that all the oximes promoted the ‘superoot’ phenotype. All this matches with the hypothesis that IAOx exerts its signalling by liberating NO. This new knowledge is a step forward towards the discovery of an oxidative NO synthesis pathway in plants and throws light into the interplay between IAOx, IAA and nitrogen nutrition, which will be paramount for further field research in crop production.