RESUMEN
MAIN CONCLUSION: Microbacterium strain SRS2 promotes growth and induces salt stress resistance in Arabidopsis and MicroTom in various growth substrates via the induction of the ABA pathway. Soil salinity reduces plant growth and development and thereby decreases the value and productivity of soils. Plant growth-promoting rhizobacteria (PGPR) have been shown to support plant growth such as in salt stress conditions. Here, Microbacterium strain SRS2, isolated from the root endosphere of tomato, was tested for its capability to help plants cope with salt stress. In a salt tolerance assay, SRS2 grew well up to medium levels of NaCl, but the growth was inhibited at high salt concentrations. SRS2 inoculation led to increased biomass of Arabidopsis and MicroTom tomato in various growth substrates, in the presence and in the absence of high NaCl concentrations. Whole-genome analysis revealed that the strain contains several genes involved in osmoregulation and reactive oxygen species (ROS) scavenging, which could potentially explain the observed growth promotion. Additionally, we also investigated via qRT-PCR, promoter::GUS and mutant analyses whether the abscisic acid (ABA)-dependent or -independent pathways for tolerance against salt stress were involved in the model plant, Arabidopsis. Especially in salt stress conditions, the plant growth-promotion effect of SRS2 was lost in aba1, abi4-102, abi3, and abi5-1 mutant lines. Furthermore, ABA genes related to salt stress in SRS2-inoculated plants were transiently upregulated compared to mock under salt stress conditions. Additionally, SRS2-inoculated ABI4::GUS and ABI5::GUS plants were slightly more activated compared to the uninoculated control under salt stress conditions. Together, these assays show that SRS2 promotes growth in normal and in salt stress conditions, the latter possibly via the induction of ABA-dependent and -independent pathways.
Asunto(s)
Ácido Abscísico , Arabidopsis , Microbacterium , Estrés Salino , Solanum lycopersicum , Arabidopsis/genética , Arabidopsis/microbiología , Arabidopsis/crecimiento & desarrollo , Arabidopsis/fisiología , Solanum lycopersicum/microbiología , Solanum lycopersicum/crecimiento & desarrollo , Solanum lycopersicum/genética , Solanum lycopersicum/fisiología , Ácido Abscísico/metabolismo , Microbacterium/genética , Microbacterium/fisiología , Tolerancia a la Sal/genética , Raíces de Plantas/microbiología , Raíces de Plantas/crecimiento & desarrollo , Raíces de Plantas/genética , Especies Reactivas de Oxígeno/metabolismo , Cloruro de Sodio/farmacología , Regulación de la Expresión Génica de las Plantas/efectos de los fármacosRESUMEN
Alternaria species, primarily the small-spored Alternaria alternata and the large-spored Alternaria solani, are considered a serious threat to potato cultivation. To develop control strategies, it is important to gain insight into the Alternaria population. Based on the sequence analyses of the internal transcribed spacer region (ITS) and the glyceraldehyde-3-phosphate dehydrogenase gene, the small-spored and large-spored Alternaria isolates could be separated from each other. Sequence analyses of the calmodulin gene and the RNA polymerase second largest subunit showed that besides A. solani also A. grandis and A. protenta were present in the large-spored Alternaria population. Sequence analyses of the Alternaria major allergen gene Alt a 1 and the elongation factor-α revealed that both A. alternata and species belonging to the Alternaria arborescens species complex were present in the small-spored Alternaria population. Furthermore, according to the histone h3 sequence the members of the A. arborescens species complex could be subdivided into two groups. Concerning the fitness, it was concluded that the mycelium growth rate of the large-spored isolates was significantly lower compared to the growth rate of the small-spored isolates. In contrast, the spore-germinating capacity and early growth of the large-spored isolates was greater compared to those of the small-spored isolates. Within the groups of small-spored and large-spored isolates there were no significant differences in fitness between the species.