Cold stress triggers freezing tolerance in wheat (Triticum aestivum L.) via hormone regulation and transcription of related genes

Low temperatures limit the geographic distribution and yield of plants. Hormones play an important role in coordinating the growth and development of plants and their tolerance to low temperatures. However, the mechanisms by which hormones affect plant resistance to extreme cold stress in the natural environment are still unclear. In this study, two winter wheat varieties with different cold resistances, Dn1 and J22, were used to conduct targeted plant hormone metabolome analysis on the tillering nodes of winter wheat at 5 °C, -10 °C and -25 °C using an LC-ESI-MS/MS system. We screened 39 hormones from 88 plant hormone metabolites and constructed a partial regulatory network of auxin, jasmonic acid and cytokinin. GO analysis and enrichment of KEGG pathways in different metabolites showed that the 'plant hormone signal transduction' pathway was the most common. Our study showed that extreme low temperature increased the most levels of auxin, cytokinin and salicylic acid, and decreased levels of jasmonic acid and abscisic acid, and that levels of auxin, jasmonic acid and cytokinin in Dn1 were higher than those in J22. These changes in hormone levels were associated with changes in gene expression in synthesis, catabolism, transport and signal transduction pathways. These results differ from the previous hormone regulation mechanisms, which were mostly obtained at 4 °C. Our results provide a basis for further understanding the molecular mechanisms by which plant endogenous hormones regulate plant freezing stress tolerance.

Adaptability of winter wheat Dongnongdongmai 1 (Triticum aestivum L.) to overwintering in alpine regions

Long winters led to a one-crop-a-year cultivation system until the winter wheat Dongnongdongmai 1 (Dn1) was successfully cultivated in northeast China. This crop variety is resistant to extremely low temperatures (-35 °C). To better understand the adaptability of winter wheat Dn1 to low temperatures, gas chromatography time-of-flight mass spectrometry (GC-TOF/MS) and metabolomics analysis was conducted on the tillering nodes of winter wheat during the overwintering period. Enzyme-regulating genes of the metabolic products were also quantitatively analysed. The metabolomic results for the tillering nodes in the overwintering period showed that disaccharides had a strong protective effect on winter wheat Dn1. Amino acid metabolism (i.e. proline, alanine and GABA) changed significantly throughout the whole wintering process, whereas organic fatty acid metabolism changed significantly only in the late stage of overwintering. This result indicates that the metabolites used by winter wheat Dn1 differ in different overwintering stages. The relationship between field temperature and metabolite changes in winter wheat Dn1 during overwintering periods is discussed, and disaccharides were identified as the osmotic stress regulators for winter wheat Dn1 during the overwintering process, as well as maintenance of the carbon and nitrogen balance by monosaccharides, amino acids and lipids for cold resistance.

Identification and characterization of long non-coding RNAs as competing endogenous RNAs in the cold stress response of Triticum aestivum

Long non-coding RNAs (lncRNAs) play important roles in plant development and stress responses. MicroRNAs (miRNAs) are involved in transcriptional and post-transcriptional gene regulation. It is not clear how lncRNA-mediated plant responses to cold stress and how lncRNAs, miRNAs and target mRNAs cooperate subject to the competing endogenous RNA (ceRNA). We interpreted the function of lncRNAs in the winter wheat cultivar Dongnongdongmai 1 (Dn1). A total of 9970 putative lncRNAs were initially identified from three Dn1 lncRNA libraries (5 °C, -10 °C and -25 °C) using high-throughput sequencing. Among the 14,626 genes detected via weighted gene co-expression network analysis, 7435 lncRNAs were co-expressed with 7191 mRNAs. We found six modules related to cold resistance in the lncRNA-mRNA weighted co-expression network, and the functions of mRNAs were similar in each module. Antioxidant systems and hormones played important roles in low-temperature responses. RNA sequencing analysis revealed that interactions between the 384 lncRNAs and 70 miRNAs were required for ceRNA activity. According to ceRNA activity, 225 lncRNAs, 60 miRNAs and 621 target mRNAs were involved in the regulatory networks of the cold stress response. Notably, a conserved region was found in the complementary regions of lncRNAs and miR164/408 but had reverse expression trends in the ceRNA network. Our results reveal possible roles of lncRNAs-mRNAs in the regulatory networks associated with tolerance to low temperature and provide useful information for more strategic use of genomic resources in wheat breeding.

Neonatal sevoflurane anesthesia induces long-term memory impairment and decreases hippocampal PSD-95 expression without neuronal loss

AIM

Volatile anesthetics are widely used in the clinic, and sevoflurane is the most prevalent volatile anesthetic in pediatric anesthesia. Recent findings question the potential risks of volatile anesthetics on brain development. Evidence suggests that sevoflurane may cause neuronal deficiency. This study investigates the long-term effect of sevoflurane in the developing brain.

MATERIALS AND METHODS

We anesthetized 7 day-old rats for 4 h with 2.5% sevoflurane. A Morris water maze was used to evaluate hippocampal function 7 weeks after sevoflurane exposure. Nissl staining was performed to analyze neuronal loss. PSD-95 (postsynaptic density protein-95) expression in the hippocampus was measured using a western blot.

RESULTS

The exposure to 2.5% sevoflurane caused long-term deficits in hippocampal function and decreased hippocampal PSD-95 expression without neuronal loss. This study demonstrates that P7 rats exposed for 4 h to 2.5% sevoflurane have significant spatial learning and memory impairment 7 weeks after anesthesia. In addition, PSD-95 expression in the hippocampus decreased at P56 without neuronal loss.

CONCLUSIONS

These data suggest that sevoflurane causes neurotoxicity in the developing brain, which may be attributed to decreased PSD-95 in the hippocampus.

Sensory and central mechanisms control intersegmental coordination

Recent experiments on the sensory and central mechanisms that coordinate animal locomotory movements have advanced our understanding of the relative importance of these two components and overturned some previously held notions. In different experimental preparations, sensory inputs and central pattern generators have now been shown to play different roles in setting intersegmental phase lags.

Sensory modification of leech swimming: interactions between ventral stretch receptors and swim-related neurons

The neuronal circuits that generate the leech swimming rhythm comprise oscillatory interneurons that provide appropriately phased output to drive swim-related motoneurons. Within ganglia, these interneurons express three phases; between ganglia there exists a phase delay between homologs. Our earlier experiments revealed that stretch receptors embedded in the body wall participate in intersegmental coordination and setting intersegmental phases. To identify the basis for these sensory effects, we mapped interactions between a ventral stretch receptor and swim-related neurons. Connections between this receptor and motoneurons are weak and variable in quiescent preparations, but during fictive swimming stretch receptor activation modulates motoneuron oscillations, hence, these effects are polysynaptic, mediated by interneurons. We identified a strong, nonrectifying, and apparently direct electrical connection between the stretch receptor and oscillator neuron 33. The ventral stretch receptor also interacts with most of the other oscillatory interneurons, including inhibitory inputs to cells 28 and 208, excitatory input to the contralateral cell 115, and mixed input to the ipsilateral cell 115. These direct and indirect interactions can account for previously described effects of body-wall stretch on motoneuron activity. They also could mediate the previously described modification of intersegmental phase relationships by appropriately phased stretch receptor activation.

Sensory modification of leech swimming: rhythmic activity of ventral stretch receptors can change intersegmental phase relationships

For segmented animals to generate optimal locomotory movements, appropriate phase relationships between segmental oscillators are crucial. Using swimming leeches, we have investigated the role of sensory input in establishing such relationships. We found that the stretch receptors associated with ventral longitudinal muscles encode the information of muscle contraction during swimming via membrane potential oscillations, with amplitudes of up to 10 mV at our recording site. We subsequently modified the activity of ventral stretch receptors (VSRs) by injecting rhythmic current at different phases of the swim cycle and determined intersegmental phase lags by comparing the delay between the discharges of serially homologous motoneurons in three adjacent segments of isolated nerve cords. When no current was injected, the phase lag between neighboring segments was 8.6 +/- 0.8 degrees (mean +/- SEM; n = 20), with large phase variations from cycle to cycle, between different episodes, and between different preparations. When the phase of stretch receptor activity was set to 90-150 degrees by current injection, the phase of the motoneuron activity in the ganglion was consistently retarded by approximately 5 degrees. It was advanced by approximately 5 degrees when the VSR phase was set to 240-300 degrees. Therefore, the rhythmic activity of the ventral stretch receptor generated during swimming can change intersegmental phase lags of leech ganglia in a phase-dependent manner. These stretch receptors may set the optimal intersegmental phases during swimming movement in intact leeches.