RESUMO
To ensure food security given the current scenario of climate change and the accompanying ecological repercussions, it is essential to search for new technologies and tools for agricultural production. Microorganism-based biostimulants are recognized as sustainable alternatives to traditional agrochemicals to enhance and protect agricultural production. Marine actinobacteria are a well-known source of novel compounds for biotechnological uses. In addition, former studies have suggested that coral symbiont actinobacteria may support co-symbiotic photosynthetic growth and tolerance and increase the probability of corals surviving abiotic stress. We have previously shown that this activity may also hold in terrestrial plants, at least for the actinobacteria Salinispora arenicola during induced heterologous symbiosis with a wild Solanaceae plant Nicotiana attenuata under in vitro conditions. Here, we further explore the heterologous symbiotic association, germination, growth promotion, and stress relieving activity of S. arenicola in tomato plants under agricultural conditions and dig into the possible associated mechanisms. Tomato plants were grown under normal and saline conditions, and germination, bacteria-root system interactions, plant growth, photosynthetic performance, and the expression of salt stress response genes were analyzed. We found an endophytic interaction between S. arenicola and tomato plants, which promotes germination and shoot and root growth under saline or non-saline conditions. Accordingly, photosynthetic and respective photoprotective performance was enhanced in line with the induced increase in photosynthetic pigments. This was further supported by the overexpression of thermal energy dissipation, which fine-tunes energy use efficiency and may prevent the formation of reactive oxygen species in the chloroplast. Furthermore, gene expression analyses suggested that a selective transport channel gene, SlHKT1,2, induced by S. arenicola may assist in relieving salt stress in tomato plants. The fine regulation of photosynthetic and photoprotective responses, as well as the inhibition of the formation of ROS molecules, seems to be related to the induced down-regulation of other salt stress response genes, such as SlDR1A-related genes or SlAOX1b. Our results demonstrate that the marine microbial symbiont S. arenicola establishes heterologous symbiosis in crop plants, promotes growth, and confers saline stress tolerance. Thus, these results open opportunities to further explore the vast array of marine microbes to enhance crop tolerance and food production under the current climate change scenario.
RESUMO
ABSTRACT The experimental infection of Arabidopsis thaliana by the maize phytopathogenic hemibasidiomycete Ustilago maydis under axenic conditions is described. When plantlets were inoculated with mixtures of compatible haploids, the fungus was able to grow on the plant surface of inoculated seedlings in the form of white mycelium and invade the tissues, probably penetrating through stomata; however, it did not form teliospores. Symptoms of disease were increased anthocyanin formation, development of chlorosis, increased formation of secondary roots, induction of malformations in the leaves and petioles, induction of tissue necrosis, and stunting. In several cases, death of the invaded plants occurred. Interestingly, inoculation of single U. maydis haploid strains produced similar symptoms in Arabidopsis plantlets. In contrast, several mutants avirulent to maize also were avirulent or less virulent than wildtype strains on Arabidopsis. Collectively, the reported data suggest that the U. maydis-Arabidopsis pathosystem may constitute a useful experimental model for the analysis of some aspects of the virulence factors of the fungus. With the study of nonhost responses and their comparison to those occurring during maize infection, we will be able to elucidate some obscure aspects of U. maydis pathogenicity in the future.