Metabolome and transcriptome reprogramming underlying tomato drought resistance triggered by a Pseudomonas strain.

Although amelioration of drought stress by Plant Growth Promoting Rhizobacteria (PGPR) is a well-documented phenomenon, the combined molecular and metabolic mechanisms governing this process remain unclear. In these lines, the present study aimed to provide new insights in the underlying drought attenuating mechanisms of tomato plants inoculated with a PGP Pseudomonas putida strain, by using a combination of metabolomic and transcriptomic approaches. Following Differentially Expressed Gene analysis, it became evident that inoculation resulted in a less disturbed plant transcriptome upon drought stress. Untargeted metabolomics highlighted the differential metabolite accumulation upon inoculation, as well as the less metabolic reprograming and the lower accumulation of stress-related metabolites for inoculated stressed plants. These findings were in line with morpho-physiological evidence of drought stress mitigation in the inoculated plants. The redox state modulation, the more efficient nitrogen assimilation, as well as the differential changes in amino acid metabolism, and the induction of the phenylpropanoid biosynthesis pathway, were the main drought-attenuating mechanisms in the SAESo11-inoculated plants. Shifts in pathways related to hormonal signaling were also evident upon inoculation at a transcript level and in conjunction with carbon metabolism regulation, possibly contributed to a drought-attenuation preconditioning. The identified signatory molecules of SAESo11-mediated priming against drought included aspartate, myo-inositol, glutamate, along with key genes related to trehalose, tryptophan and cysteine synthesis. Taken together, SAESo11-inoculation provides systemic effects encompassing both metabolic and regulatory functions, supporting both seedling growth and drought stress amelioration.

Impacts of Decaying Aromatic Plants on the Soil Microbial Community and on Tomato Seedling Growth and Metabolism: Suppression or Stimulation?

This study provides insight into changes in the features of tomato seedlings growing in soils enriched with spearmint, peppermint, or rosemary leaves and into changes in the microbial communities of these soils used as seedbeds; an organic amendment was also applied as a positive control. While the soil microbial community flourished in the presence of all three aromatic plants, tomato growth was inhibited or stimulated depending on the plant that was used. More specifically, phospholipid fatty acid (PLFA) analysis showed an increase in the total microbial biomass and in the biomass of all the groups examined, except for actinobacteria, and changes in the microbial community structure, with Gram-negative bacteria and fungi being favoured in the mint treatments, in which the microbial biomass was maximized. Seedlings from the rosemary treatment were entirely inhibited; they were at the open-cotyledon stage throughout the experiment. Seedlings from the mint treatments were the heaviest, longest, and had the highest chlorophyll content and photosynthetic yield. Metabolomic analysis showed metabolism enhancement associated with both growth and priming in seedlings from the mint treatments and disruption of metabolic pathways in those from the rosemary treatment. There is a great potential for applying these aromatic plants as soil amendments and as either biostimulants of plant growth or as herbicides.

Comparative Transcriptomics and Metabolomics Reveal an Intricate Priming Mechanism Involved in PGPR-Mediated Salt Tolerance in Tomato.

Plant-associated beneficial strains inhabiting plants grown under harsh ecosystems can help them cope with abiotic stress factors by positively influencing plant physiology, development, and environmental adaptation. Previously, we isolated a potential plant growth promoting strain (AXSa06) identified as Pseudomonas oryzihabitans, possessing 1-aminocyclopropane-1-carboxylate deaminase activity, producing indole-3-acetic acid and siderophores, as well as solubilizing inorganic phosphorus. In this study, we aimed to further evaluate the effects of AXSa06 seed inoculation on the growth of tomato seedlings under excess salt (200 mM NaCl) by deciphering their transcriptomic and metabolomic profiles. Differences in transcript levels and metabolites following AXSa06 inoculation seem likely to have contributed to the observed difference in salt adaptation of inoculated plants. In particular, inoculations exerted a positive effect on plant growth and photosynthetic parameters, imposing plants to a primed state, at which they were able to respond more robustly to salt stress probably by efficiently activating antioxidant metabolism, by dampening stress signals, by detoxifying Na+, as well as by effectively assimilating carbon and nitrogen. The primed state of AXSa06-inoculated plants is supported by the increased leaf lipid peroxidation, ascorbate content, as well as the enhanced activities of antioxidant enzymes, prior to stress treatment. The identified signatory molecules of AXSa06-mediated salt tolerance included the amino acids aspartate, threonine, serine, and glutamate, as well as key genes related to ethylene or abscisic acid homeostasis and perception, and ion antiporters. Our findings represent a promising sustainable solution to improve agricultural production under the forthcoming climate change conditions.

Integrated analysis of metabolites and proteins reveal aspects of the tissue-specific function of synthetic cytokinin in kiwifruit development and ripening.

UNLABELLED: Fruit development and ripening depends on highly coordinated phyto-hormonal activities. Although the role of synthetic cytokinin N-(2-chloro-4-pyridyl)-N'-phenylurea (CPPU) in promoting fruit growth has been established, knowledge regarding the underlying mechanism is still lacking. Here, we characterize the effect of CPPU application 20d after full bloom at pre- and post-harvest biology of kiwifruit (Actinidia deliciosa [A. Chev.] C.F. Liang et A.R. Ferguson var. deliciosa cv. 'Hayward'). Data revealed that CPPU stimulates kiwifruit growth through the enlargement of small cells. During fruit development, the abundance of 16 proteins that are mainly related to defence was increased by CPPU while CPPU altered the expression of 19 polar metabolites in outer pericarp. Sugar homeostasis, cell wall modifications, TCA cycle and myo-inositol pathway were mostly affected by CPPU in kiwifruit during development. Upon postharvest ripening at 20°C following 2months of cold storage (0°C), CPPU suppressed ethylene production and retained central placenta softening, indicating that CPPU induced tissue-dependent disturbances in climacteric ripening. Nineteen central placenta proteins and up to 15 metabolites of outer pericarp and central placenta tissues were affected by CPPU in ripened kiwifruits. These observations amplified our understanding in the regulation of fruit development and ripening by exogenously supplied cytokinins. BIOLOGICAL SIGNIFICANCE: This study demonstrates that CPPU application, apart from fruit development, influenced also the kiwifruit climacteric ripening behaviour. An insight on the action of CPPU during kiwifruit development is provided, showing that it is partially based on a general stimulation of TCA cycle and myo-inositol pathway along with alternation in sugar and cell wall metabolism. Data also revealed that CPPU regulates ethylene biosynthesis and influences central placenta softening, indicating that this tissue may play a prominent role in kiwifruit ripening. Also, this work provides a first characterization of the ripening-affected central placenta proteins that offers insights into kiwifruit ripening. The current study provides a baseline of information for understanding the metabolic processes that are regulated by exogenous cytokinin during fruit development and ripening.