MdPRX34L, a class III peroxidase gene, activates the immune response in apple to the fungal pathogen Botryosphaeria dothidea.

MAIN CONCLUSION: MdPRX34L enhanced resistance to Botryosphaeria dothidea by increasing salicylic acid (SA) and abscisic acid (ABA) content as well as the expression of related defense genes. The class III peroxidase (PRX) multigene family is involved in complex biological processes. However, the molecular mechanism of PRXs in the pathogen defense of plants against Botryosphaeria dothidea (B. dothidea) remains unclear. Here, we cloned the PRX gene MdPRX34L, which was identified as a positive regulator of the defense response to B. dothidea, from the apple cultivar 'Royal Gala.' Overexpression of MdPRX34L in apple calli decreased sensitivity to salicylic acid (SA) and abscisic acid（ABA). Subsequently, overexpression of MdPRX34L in apple calli increased resistance to B. dothidea infection. In addition, SA contents and the expression levels of genes related to SA synthesis and signaling in apple calli overexpressing MdPRX34L were higher than those in the control after inoculation, suggesting that MdPRX34L enhances resistance to B. dothidea via the SA pathway. Interestingly, infections in apple calli by B. dothidea caused an increase in endogenous levels of ABA followed by induction of ABA-related genes expression. These findings suggest a potential mechanism by which MdPRX34L enhances plant-pathogen defense against B. dothidea by regulating the SA and ABA pathways.

Role of reactive oxygen species in lesion mimic formation and conferred basal resistance to Fusarium graminearum in barley lesion mimic mutant 5386.

This study investigated the barley lesion mimic mutant (LMM) 5386, evidenced by a leaf brown spot phenotype localized on the chromosome 3H, and its conferred basal resistance to Fusarium graminearum. RNA-seq analysis identified 1453 genes that were differentially expressed in LMM 5386 compared to those in the wild type. GO and KEGG functional annotations suggested that lesion mimic formation was mediated by pathways involving oxidation reduction and glutathione metabolism. Additionally, reactive oxygen species (ROS) accumulation in brown spots was substantially higher in LMM 5386 than in the wild-type plant; therefore, antioxidant competence, which is indicated by ROS accumulation, was significantly lower in LMM 5386. Furthermore, the reduction of glycine in LMM 5386 inhibited glutathione biosynthesis. These results suggest that the decrease in antioxidant competence and glutathione biosynthesis caused considerable ROS accumulation, leading to programmed cell death, which eventually reduced the yield components in LMM 5386.

Conversion from Nonshockable to Shockable Rhythms and Out-of-Hospital Cardiac Arrest Outcomes by Initial Heart Rhythm and Rhythm Conversion Time.

BACKGROUND: The conversion from a nonshockable rhythm (asystole or pulseless electrical activity (PEA)) to a shockable rhythm (pulseless ventricular tachycardia or ventricular fibrillation) may be associated with better out-of-hospital cardiac arrest (OHCA) outcomes. There are insufficient data on the prognostic significance of such conversions by initial heart rhythm and different rhythm conversion time. METHODS: Among 24,849 adult OHCA patients of presumed cardiac etiology with initial asystole or PEA in the Resuscitation Outcomes Consortium Cardiac Epidemiologic Registry (version 3, 2011-2015), we examined the association of shockable rhythm conversion with prehospital return of spontaneous circulation (ROSC), survival, and favorable functional outcome (modified Rankin Scale score ≤3) at hospital discharge by initial rhythm and rhythm conversion time (time from cardiopulmonary resuscitation (CPR) initiation by emergency medical providers to first shock delivery), using logistic regression adjusting for key clinical characteristics. RESULTS: Of 16,516 patients with initial asystole and 8,333 patients with initial PEA, 16% and 20% underwent shockable rhythm conversions; the median rhythm conversion time was 12.0 (IQR: 6.7-18.7) and 13.2 (IQR: 7.0-20.5) min, respectively. No difference was found in odds of prehospital ROSC across rhythm conversion time, regardless of initial heart rhythm. Shockable rhythm conversion was associated with survival and favorable functional outcome at hospital discharge only when occurred during the first 15 min of CPR, for those with initial asystole, or the first 10 min of CPR, for those with initial PEA. The associations between shockable rhythm conversion and outcomes were stronger among those with initial asystole compared with those with initial PEA. CONCLUSIONS: The conversion from a nonshockable rhythm to a shockable rhythm was associated with better outcomes only when occurred early in initial nonshockable rhythm OHCA, and it has greater prognostic significance when the initial rhythm was asystole.

Adult-born neurons facilitate olfactory bulb pattern separation during task engagement.

The rodent olfactory bulb incorporates thousands of newly generated inhibitory neurons daily throughout adulthood, but the role of adult neurogenesis in olfactory processing is not fully understood. Here we adopted a genetic method to inducibly suppress adult neurogenesis and investigated its effect on behavior and bulbar activity. Mice without young adult-born neurons (ABNs) showed normal ability in discriminating very different odorants but were impaired in fine discrimination. Furthermore, two-photon calcium imaging of mitral cells (MCs) revealed that the ensemble odor representations of similar odorants were more ambiguous in the ablation animals. This increased ambiguity was primarily due to a decrease in MC suppressive responses. Intriguingly, these deficits in MC encoding were only observed during task engagement but not passive exposure. Our results indicate that young olfactory ABNs are essential for the enhancement of MC pattern separation in a task engagement-dependent manner, potentially functioning as a gateway for top-down modulation.

Lack of Pattern Separation in Sensory Inputs to the Olfactory Bulb during Perceptual Learning.

Recent studies revealed changes in odor representations in the olfactory bulb during active olfactory learning (Chu et al., 2016; Yamada et al., 2017). Specifically, mitral cell ensemble responses to very similar odorant mixtures sparsened and became more distinguishable as mice learned to discriminate the odorants over days (Chu et al., 2016). In this study, we explored whether changes in the sensory inputs to the bulb underlie the observed changes in mitral cell responses. Using two-photon calcium imaging to monitor the odor responses of the olfactory sensory neuron (OSN) axon terminals in the glomeruli of the olfactory bulb during a discrimination task, we found that OSN inputs to the bulb are stable during discrimination learning. During one week of training to discriminate between very similar odorant mixtures in a Go/No-go task, OSN responses did not show significant sparsening, and the responses to the trained similar odorants did not diverge throughout training. These results suggest that the adaptive changes of mitral cell responses during perceptual learning are ensured by mechanisms downstream of OSN input, possibly in local circuits within olfactory bulb.

Balancing the Robustness and Efficiency of Odor Representations during Learning.

For reliable stimulus identification, sensory codes have to be robust by including redundancy to combat noise, but redundancy sacrifices coding efficiency. To address how experience affects the balance between the robustness and efficiency of sensory codes, we probed odor representations in the mouse olfactory bulb during learning over a week, using longitudinal two-photon calcium imaging. When mice learned to discriminate between two dissimilar odorants, responses of mitral cell ensembles to the two odorants gradually became less discrete, increasing the efficiency. In contrast, when mice learned to discriminate between two very similar odorants, the initially overlapping representations of the two odorants became progressively decorrelated, enhancing the robustness. Qualitatively similar changes were observed when the same odorants were experienced passively, a condition that would induce implicit perceptual learning. These results suggest that experience adjusts odor representations to balance the robustness and efficiency depending on the similarity of the experienced odorants.