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The exponential growth of the population, the trend towards organic food consumption and the increasingly restrictive regulations imposed by the European Union are forcing the agricultural sector to evolve towards more sustainable practices that are less harmful to the environment. In addition to these challenges, farmers need to cope with other biotic and abiotic factors affecting plant productivity, such as drought, diseases and pests. To that end, biotechnological approaches to obtain food in a sustainable way are being explored. The lower Guadalquivir region, at the South of Spain, contains the largest area devoted to intensive agriculture practices in Andalusia. This region faces two main problems, which are high salinity in irrigation water and N contamination by synthetic fertilizers (Paredes et al., 2020). In this work we provide two different biotechnological approaches to address these problems: 1) We have characterized salt resistance in nine rice varieties that are being cultivated in the Guadalquivir paddies. This analysis has been complemented through morphological, physiological and biochemical approaches, using analytical methods such as HPLC and mass chromatography, among others. We have identified metabolites that are overproduced in salt stress conditions and might be used for the early detection of salt stress in the plant. A comparative analysis of the different rice varieties analysed provided valued information about the different tolerance to salt. 2) In order to reduce the use of synthetic nitrogen fertilizers, we tested three bioinoculants that had been previously isolated from cotton soils. First, we characterized them biochemically for the PGPR activities, comprising N2 fixation and production of plant phytohormones. Effectiveness of these bioinoculants was assayed in microcosms experiments. We found a significant plant growth stimulation in two of the three bioinoculants evaluated.

Motivation: Cyanobacteria of the genus Nostoc are capable of establishing symbiosis relationships with many different types of plants. In these mutualistic relationships the cyanobacterium provides the plant with fixed nitrogen, while the plant provides the cyanobacterium with protection from hostile environments and carbon compounds as energy for N2 fixation. It has recently been described that Nostoc punctiforme performs a stable symbiosis with Oryza sativa (Álvarez et al., 2020). In order to know the molecular mechanisms involved in the recognition between the plant and the cyanobacterium, a proteomic study was carried out in the early stages of co-culture of both organisms. In this study, proteins with homology to the Nod factors of Rhizobium sp. were identified in Nostoc, which could be related to signaling in the plant. The aim of this work is to study the regulation of the expression of the genes encoding these Nod proteins by means of RT-qPCR. Methods: The expression of Nostoc punctiforme Nod genes was studied in response to the presence of the plant at 1, 2, 3, 5 and 7 days of co-culture. On the one hand, a Nostoc punctiforme culture grown at 25°C in Roux flasks with 1% CO2, continuous illumination and at 30°C was prepared. On the other hand, Oryza sativa seedlings were obtained germination of seeds under axenic conditions. At one week of growth, the seedlings were transplanted into flasks with hydroponic medium. Co-culture was performed by adding a fixed amount of Nostoc to the Oryza culture medium, and incubating the mixture in thermostated chambers at 25°C, 12h light/dark cycles and 75% relative humidity. RNA was extracted from Nostoc samples that had been in contact with the plant. As a control, Nostoc incubated without the plant was used. After RNA retrotranscription, the resulting cDNA was used to evaluate the expression of the genes of interest. Results: It was observed that the expression of certain Nod genes is activated in the presence of Oryza, although there are other Nod genes whose expression remains unchanged in response to inoculation with the plant.