Comparative Functional Genomics of Salt Stress in Related Model and Cultivated Plants Identifies and Overcomes Limitations to Translational Genomics

One of the objectives of plant translational genomics is to use knowledge and genes discovered in model species to improve crops. However, the value of translational genomics to plant breeding, especially for complex traits like abiotic stress tolerance, remains uncertain. Using comparative genomics (ionomics, transcriptomics and metabolomics) we analyzed the responses to salinity of three model and three cultivated species of the legume genus Lotus. At physiological and ionomic levels, models responded to salinity in a similar way to crop species, and changes in the concentration of shoot Cl− correlated well with tolerance. Metabolic changes were partially conserved, but divergence was observed amongst the genotypes. Transcriptome analysis showed that about 60% of expressed genes were responsive to salt treatment in one or more species, but less than 1% was responsive in all. Therefore, genotype-specific transcriptional and metabolic changes overshadowed conserved responses to salinity and represent an impediment to simple translational genomics. However, ‘triangulation’ from multiple genotypes enabled the identification of conserved and tolerant-specific responses that may provide durable tolerance across species

Thermospermine catabolism increases Arabidopsis thaliana resistance to Pseudomonas viridiflava

This work investigated the roles of the tetraamine thermospermine (TSpm) by analysing its contribution to Arabidopsis basal defence against the biotrophic bacterium Pseudomonas viridiflava. The participation of polyamine oxidases (PAOs) in TSpm homeostasis and TSpm-mediated defence was also investigated. Exogenous supply of TSpm, as well as ectopic expression of the TSpm biosynthetic gene ACL5, increased Arabidopsis Col-0 resistance to P. viridiflava, while null acl5 mutants were less resistant than Col-0 plants. The above-mentioned increase in resistance was blocked by the PAO inhibitor SL-11061, thus demonstrating the participation of TSpm oxidation. Analysis of PAO genes expression in transgenic 35S::ACL5 and Col-0 plants supplied with TSpm suggests that PAO 1, 3, and 5 are the main PAOs involved in TSpm catabolism. In summary, TSpm exhibited the potential to perform defensive functions previously reported for its structural isomer Spm, and the relevance of these findings is discussed in the context of ACL5 expression and TSpm concentration in planta. Moreover, this work demonstrates that manipulation of TSpm metabolism modifies plant resistance to pathogens.The gift of SL-11061 by Dr Frydman (SLIL Biomedical Corporation, Madison, WI) is greatly appreciated. This work was supported by Consejo Nacional de Investigaciones Cientificas y Tecnicas (CONICET), Argentina (PIP 5740, PIP 0395), Agencia Nacional de Promocion Cientifica y Tecnologica, Argentina (PICT 1119, ANPCYT), Universidad Nacional de General San Martin, Argentina (SJ10/30), Ministerio de Economia y Competitividad, Spain (BIO2011-23828), and Fundacion Carolina (postdoctoral fellowship to MM). MM, FLP, and OAR are members of the Research Career of CONICET.Marina, M.; Vera Sirera, FJ.; Rambla Nebot, JL.; Gonzalez, ME.; Blazquez Rodriguez, MA.; Carbonell Gisbert, J.; Pieckenstain, FL.... (2013). Thermospermine catabolism increases Arabidopsis thaliana resistance to Pseudomonas viridiflava. Journal of Experimental Botany. 64(5):1393-1402. https://doi.org/10.1093/jxb/ert012S13931402645Alonso, J. M. (2003). Genome-Wide Insertional Mutagenesis of Arabidopsis thaliana. Science, 301(5633), 653-657. doi:10.1126/science.1086391Alippi, A. M., Dal Bo, E., Ronco, L. B., Lopez, M. V., Lopez, A. C., & Aguilar, O. M. (2003). Pseudomonas populations causing pith necrosis of tomato and pepper in Argentina are highly diverse. Plant Pathology, 52(3), 287-302. doi:10.1046/j.1365-3059.2003.00850.xAngelini, R., Bragaloni, M., Federico, R., Infantino, A., & Porta-Pugua, A. (1993). Involvement of Polyamines, Diamine Oxidase and Peroxidase in Resistance of Chickpea to Ascochyta rabiei. 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Pantoea eucalyptii induces systemic resistance in Arabidopsis thaliana against Botrytis cinerea by priming defense responses

Many endophytic bacteria colonize host tissues internally without causing damage or eliciting disease symptoms. Some of them also promote plant growth. Previously, we obtained a collection of bacterial endophytes from leaves of field-grown tomato and identified strains capable to systemically protect this plant against B. cinerea infection. In the present work we used the model plant A. thaliana to analyze the mechanisms involved in the induction of systemic resistance to B. cinerea by one of these strains, Pantoea eucalypti NT6 (PeNT6). In order to evaluate if PeNT6 triggers induced systemic resistance (ISR) in A. thaliana, plants were soil-inoculated with this bacterium and challenged by leaf inoculation with B. cinerea four weeks later. PeNT6 inoculation reduced (30-60%) the size of necrotic lesions caused by B. cinerea. Inoculation with PeNT6 had no effect on the expression of the defense-related genes PR1, PDF1.2, MPK3 and WRKY33. However, plants inoculated with PeNT6 and further challenged with B. cinerea exhibited higher levels of MPK3 and WRKY33 expression than those plants challenged with B. cinerea without previous inoculation with the bacterium. NT6 was unable to trigger ISR in A. thaliana mutants affected in defense signaling pathways mediated by jasmonic acid (coi1), ethylene (ein2) and salicylic acid (sid2). However, the npr1 mutant showed an ISR similar to the wild type. Mutants in MPK3 and MPK6 showed a differential response. While the mpk3 mutant showed no induction of resistance, the mpk6 showed a similar level of ISR to wild type plants. ISR triggered by PeNT6 also involved priming of callose deposition upon Botrytis infection. Finally, the use of a GFP-labeled B. cinerea strain allowed us to determine that in planta germination of fungal conidia was retarded in NT6-inoculated plants. Results hereby presented demonstrate that P. eucalypti triggers ISR to B. cinerea by priming specific components of the defense machinery, such as the kinase MPK3 and the transcription factor WRKY33. ISR triggered by NT6 was also found to depend on jasmonic acid, ethylene and salicylic acid signaling pathways, but did not depend on the regulatory protein NPR1. The kinase MPK3 was also found to play a key role in the onset of ISR by PeNT6. These findings contribute to understand the mechanisms underlying ISR to B. cinerea provided by plant inoculation with beneficial bacteria with the potential to be used as biological control agents

Botrydial confers Botrytis cinerea the ability to antagonize soil and phyllospheric bacteria

The role of the sesquiterpene botrydial in the interaction of the phytopathogenic fungus Botrytis cinerea and plant-associated bacteria was analyzed. From a collection of soil and phyllospheric bacteria, nine strains sensitive to growth -inhibition by B. cinerea were identified. B. cinerea mutants unable to produce botrydial caused no bacterial inhibition, thus demonstrating the inhibitory role of botrydial. A taxonomic analysis showed that these bacteria corresponded to different Bacillus species (six strains), Pseudomonas yamanorum (two strains) and Erwinia aphidicola (one strain). Inoculation of WT and botrydial non-producing mutants of B. cinerea along with Bacillus amyloliquefaciens strain MEP(2)18 in soil demonstrated that both microorganisms exert reciprocal inhibitory effects; the inhibition caused by B. cinerea being dependent on botrydial production. Moreover, botrydial production was modulated by the presence of B. amyloliquefaciens MEP(2)18 in confrontation assays in vitro. Purified botrydial in turn, inhibited growth of Bacillus strains in vitro and cyclic lipopeptide (surfactin) production by B. amyloliquefaciens MEP(2)18. As a whole, results demonstrate that botrydial confers B. cinerea the ability to inhibit potential biocontrol bacteria of the genus Bacillus. We propose that resistance to botrydial could be used as an additional criterion for the selection of biocontrol agents of plant diseases caused by B. cinerea. (C) 2019 British Mycological Society. Published by Elsevier Ltd. All rights reserved