Stomatal response drives between-species difference in predicted leaf water-use efficiency under elevated ozone

Impacts of Dutch elm disease-causing fungi on foliage photosynthetic characteristics and volatiles in Ulmus species with different pathogen resistance

Global warming affects the abiotic and biotic growth environment of plants, including the spread of fungal diseases such as Dutch elm disease (DED). Dutch elm disease-resistance of different Ulmus species varies, but how this is reflected in leaf-level physiological pathogen responses has not been investigated. We studied the impacts of mechanical injury alone and mechanical injury plus inoculation with the DED-causing pathogens Ophiostoma novo-ulmi subsp. novo-ulmi and O. novo-ulmi subsp. americana on Ulmus glabra, a more vulnerable species, and U. laevis, a more resistant species. Plant stress responses were evaluated for 12 days after stress application by monitoring leaf net CO2 assimilation rate (A), stomatal conductance (gs), ratio of ambient to intercellular CO2 concentration (Ca/Ci) and intrinsic water-use efficiency (A/gs), and by measuring biogenic volatile (VOC) release by plant leaves. In U. glabra and U. laevis, A was not affected by time, stressors or their interaction. Only in U. glabra, gs and Ca/Ci decreased in time, yet recovered by the end of the experiment. Although the emission compositions were affected in both species, the stress treatments enhanced VOC emission rates only in U. laevis. In this species, mechanical injury especially when combined with the pathogens increased the emission of lipoxygenase pathway volatiles and dimethylallyl diphosphate and geranyl diphosphate pathway volatiles. In conclusion, the more resistant species U. laevis had a more stable photosynthesis, but stronger pathogen-elicited volatile response, especially after inoculation by O. novo-ulmi subsp. novo-ulmi. Thus, stronger activation of defenses might underlay higher DED-resistance in this species.

Elevated ozone decreases the activity of Rubisco in poplar but not its activation under fluctuating light

Increasing tropospheric ozone (O3) is well-known to decrease leaf photosynthesis under steady-state light through reductions in biochemical capacity. However, the effects of O3 on photosynthetic induction and its biochemical limitations in response to fluctuating light remain unclear, despite the rapid fluctuations of light intensity occurring under field conditions. In this study, two hybrid poplar clones with different O3 sensitivities were exposed to elevated O3. Dynamic photosynthetic CO2 response measurements were conducted to quantify the impact of elevated O3 and exposure duration on biochemical limitations during photosynthetic induction. We found that elevated O3 significantly reduced the steady-state light-saturated photosynthetic rate, the maximum rate of carboxylation (Vcmax) and Rubisco content. In addition, elevated O3 significantly decreased the time constants for slow phases and weighting of the fast phase of the Vcmax induction in poplar clone '546' but not in clone '107'. However, elevated O3 did not affect the time, it took to reach a given percentage of full Vcmax activation or photosynthetic induction in either clone. Overall, photosynthetic induction was primarily limited by the activity of Rubisco rather than the regeneration of ribulose-1,5-biphosphate regardless of O3 concentration and exposure duration. The lack of O3-induced effects on the activation of Rubisco observed here would simplify the simulation of impacts of O3 on nonsteady-state photosynthesis in dynamic photosynthetic models.

The effects of ozone treatments on the agro-physiological parameters of tomato plants and the soil microbial community

Ozone has been applied in many processes (drinking water disinfection and wastewater treatment, among others) based on its high degree of effectiveness as a wide-spectrum disinfectant and its potential for the degradation of pollutants and pesticides. Nevertheless, the effects of irrigation with ozonated water on the soil microbial community and plant physiology and productivity at the field scale are largely unknown. Here, we assessed the impact of irrigation with ozonated water on the microbial community of a Mediterranean soil and on Solanum lycopersicum L. agro-physiology and productivity in a greenhouse experiment. For this purpose, we evaluated: i) soil physicochemical properties, soil enzyme activities, and the biomass (through analysis of microbial fatty acids) and diversity (through 16S rRNA gene and ITS2 amplicon sequencing) of the soil microbial community, and ii) the nutrient content, physiology, yield, and fruit quality of tomato plants. Overall, the soil physicochemical properties were slightly affected by the treatments applied, showing some differences between continuous and intermittent irrigation with ozonated water. Only the soil pH was significantly reduced by continuous irrigation with ozonated water at the end of the assay. Biochemical parameters (enzymatic activities) showed no significant differences between the treatments studied. The biomasses of Gram- bacteria and fungi were decreased by intermittent and continuous irrigation with ozonated water, respectively. However, the diversity, structure, and composition of the soil microbial community were not affected by the ozone treatments. Changes in soil properties slightly affected tomato plant physiology but did not affect yield or fruit quality. The stomatal conductance was reduced and the intrinsic water use efficiency was increased by continuous irrigation with ozonated water. Our results suggest that soil health and fertility were not compromised, however ozonated water treatments should be tailored to individual crop conditions to avoid adverse effects.

Bone marrow mesenchymal stem cell-derived exosomes induce the Th17/Treg imbalance in immune thrombocytopenia through miR-146a-5p/IRAK1 axis

Bone marrow mesenchymal stem cells (BMSCs) are associated with immune thrombocytopenia (ITP), the underlying mechanism has not been fully elucidated. Here, we attempted to investigate whether BMSCs can regulate Th17/Treg imbalance in ITP through the exosome pathway. We first assessed the proportions of Th17 cells and Tregs in ITP patients, showing that ITP patients exhibited an evident imbalance of Th17/Treg. BMSCs-exosomes' treatment significantly reduced Th17/Treg ratio in the CD4⁺ T cells of ITP patients. Moreover, miR-146a-5p was highly expressed in BMSCs-exosomes. The expression of miR-146a-5p was obviously increased in CD4⁺ T cells following the treatment of BMSCs-exosomes. BMSCs-exosomal miR-146a-5p silencing promoted the proportions of Th17 cells and repressed the proportions of Tregs in CD4⁺ T cells. In addition, miR-146a-5p directly interacted with IL-1R-associated kinase-1 (IRAK), and repressed IRAK1 expression. IRAK1 overexpression promoted Th17/Treg ratio in CD4⁺ T cells, which was abolished by BMSCs-exosomal miR-146a-5p. In conclusion, these findings demonstrate that BMSC-derived exosomal miR-146a-5p regulates Th17/Treg imbalance in ITP by repressing IRAK1 expression. Thus, this work suggests that BMSCs-exosomal miR-146a-5p may be a potential therapeutic target for ITP.