The transcription factors ZmNAC128 and ZmNAC130 coordinate with Opaque2 to promote endosperm filling in maize.

Endosperm filling in maize (Zea mays), which involves nutrient uptake and biosynthesis of storage reserves, largely determines grain yield and quality. However, much remains unclear about the synchronization of these processes. Here, we comprehensively investigated the functions of duplicate NAM, ATAF1/2, and CUC2 (NAC)-type transcription factors, namely, ZmNAC128 and ZmNAC130, in endosperm filling. The gene-edited double mutant zmnac128 zmnac130 exhibits a poorly filled kernel phenotype such that the kernels have an inner cavity. RNA sequencing and protein abundance analysis revealed that the expression of many genes involved in the biosynthesis of zein and starch is reduced in the filling endosperm of zmnac128 zmnac130. Further, DNA affinity purification and sequencing combined with chromatin-immunoprecipitation quantitative PCR and promoter transactivation assays demonstrated that ZmNAC128 and ZmNAC130 are direct regulators of 3 (16-, 27-, and 50-kD) γ-zein genes and 6 important starch metabolism genes (Brittle2 [Bt2], pullulanase-type starch debranching enzyme [Zpu1], granule-bound starch synthase 1 [GBSS1], starch synthase 1 [SS1], starch synthase IIa [SSIIa], and sucrose synthase 1 [Sus1]). ZmNAC128 and ZmNAC130 recognize an additional cis-element in the Opaque2 (O2) promoter to regulate its expression. The triple mutant zmnac128 zmnac130 o2 exhibits extremely poor endosperm filling, which results in more than 70% of kernel weight loss. ZmNAC128 and ZmNAC130 regulate the expression of the transporter genes sugars that will eventually be exported transporter 4c (ZmSWEET4c), sucrose and glucose carrier 1 (ZmSUGCAR1), and yellow stripe-like2 (ZmYSL2) and in turn facilitate nutrient uptake, while O2 plays a supporting role. In conclusion, ZmNAC128 and ZmNAC130 cooperate with O2 to facilitate endosperm filling, which involves nutrient uptake in the basal endosperm transfer layer (BETL) and the synthesis of zeins and starch in the starchy endosperm (SE).

Effects of Laughter Therapy on Improving Negative Emotions Associated with Cancer: A Systematic Review and Meta-Analysis.

INTRODUCTION: With aging and growth of the population, the risk of cancer incidence and mortality is rapidly increasing. However, psychosocial treatment has been seriously neglected in many healthcare settings. Laughter therapy is a therapeutic program to improve emotional wellbeing and health which has been applied as a complementary treatment. We aim to explore effects of laughter therapy for patients with cancer on their negative emotions such as depression, anxiety, stress, pain, and fatigue. METHODS: We searched the Cochrane Library, Embase, PubMed, Scopus, Web of Science, WANFANG data, Weipu (VIP), Chinese National Knowledge Infrastructure (CNKI) and independently rated the risk of bias in every article using the Cochrane Collaboration's Risk of Bias Assessment Tool. Review Manager and STATA software were used to pool the individually included studies. RESULTS: Seven studies were found eligible to be included in the present review. Overall, study quality was relatively high. Our findings suggest that laughter therapy might have a positive effect on improving emotional response in cancer patients. Arguably, laughter therapy, whether humor or laughter, has a positive effect on anxiety, stress, pain feeling, fatigue, and depression in cancer patients. CONCLUSIONS: Laughter therapy is a convenient, multi-modality, flexible-duration therapy to improve negative emotions in cancer patients, regardless of their gender, age, and type of cancer.

Mutation of KAP, which encodes a keratin-associated protein, affects grain size and yield production in rice.

Grain size and shape are critical agronomic traits that directly impact rice grain yield. Identifying genes that control these traits can provide new strategies for yield improvement. In this study, we characterized a rice mutant, reduced grain length (rgl), which exhibited decreased grain length due to reduced cell proliferation. Map-based cloning identified a base deletion in OsRGL2, a gene encoding a keratin-associated protein (KAP), as the cause of the mutant phenotype. CRISPR-Cas9-generated OsRGL2 knockout mutants also displayed reduced grain length, confirming its role. OsRGL2 transcripts were detected in various tissues, with relative higher gene expression in young panicles, and OsRGL2 was localized to the plasma membrane. Overexpression of OsRGL2 increased grain size by promoting cell proliferation in the spikelet hull and significantly enhanced grain yield per plant. Importantly, OsRGL2 was found to interact with RGB1, indicating that OsRGL2 positively regulates grain size and yield through its interaction with RGB1. Additionally, OsRGL2 regulated the expression of cell cycle-related genes, further elucidating its role in grain development. These findings demonstrate that OsRGL2 is a positive regulator of grain size in rice, and manipulating its expression may offer a novel strategy for enhancing rice grain yield.

PDE1 Inhibition Modulates Cav1.2 Channel to Stimulate Cardiomyocyte Contraction.

[Figure: see text].

Effects of reminiscence therapy combined with memory specificity training (RT-MeST) on depressive symptoms in older adults: a randomized controlled trial protocol.

BACKGROUND: Geriatric depression has become a serious public health problem, and reduced autobiographical memory and increased overgeneral memory, as the main cognitive markers of depression, are not only associated with current depressive symptoms but also associated with the onset and course of depression, which can lead to a range of harms. Economic and effective psychological interventions are urgently needed. The aim of this study is to confirm the effectiveness of reminiscence therapy combined with memory specificity training in improving autobiographical memory and depressive symptoms in older adults. METHODS: In this multicentre, single-blind, three-arm parallel randomized controlled study, we aim to enrol 78 older adults aged 65 years or older with a score of ≥ 11 on the Geriatric Depression Scale, and participants will be randomly assigned to either a reminiscence therapy group, a reminiscence therapy with memory specificity training group or a usual care group. Assessments will be conducted at baseline (T0) as well as immediately post-intervention (T1) and 1 (T2), 3 (T3) and 6 (T4) months post-intervention. The primary outcome measure is self-reported depressive symptoms, measured using the GDS. Secondary outcome measures include measures of autobiographical memory, rumination, and social engagement. DISCUSSION: We believe that the intervention will play a positive role in improving autobiographical memory and depressive symptoms in older adults. Poor autobiographical memory is a predictor of depression and a major cognitive marker, and improving autobiographical memory is of great significance in alleviating depressive symptoms in older people. If our program is effective, it will provide a convenient and feasible strategy for further promoting healthy ageing. TRIAL REGISTRATION: ChiCTR2200065446.

Effectiveness of eHealth Interventions on Moderate-to-Vigorous Intensity Physical Activity Among Patients in Cardiac Rehabilitation: Systematic Review and Meta-analysis.

BACKGROUND: Cardiac rehabilitation is a class IA recommendation for patients with cardiovascular diseases. Physical activity is the core component and core competency of a cardiac rehabilitation program. However, many patients with cardiovascular diseases are failing to meet cardiac rehabilitation guidelines that recommend moderate-to-vigorous intensity physical activity. OBJECTIVE: The major objective of this study was to review the evidence of the effectiveness of eHealth interventions in increasing moderate-to-vigorous intensity physical activity among patients in cardiac rehabilitation. The secondary objective was to examine the effectiveness of eHealth interventions in improving cardiovascular-related outcomes, that is, cardiorespiratory fitness, waist circumference, and systolic blood pressure. METHODS: A comprehensive search strategy was developed, and a systematic search of 4 electronic databases (PubMed, Web of Science, Embase, and Cochrane Library) was conducted for papers published from the start of the creation of the database until November 27, 2022. Experimental studies reporting on eHealth interventions designed to increase moderate-to-vigorous intensity physical activity among patients in cardiac rehabilitation were included. Multiple unblinded reviewers determined the study eligibility and extracted data. Risk of bias was evaluated using the Cochrane Collaboration Tool for randomized controlled trials and the Cochrane Effective Practice and Organization of Care group methods for nonrandomized controlled trials. A random-effect model was used to provide the summary measures of effect (ie, standardized mean difference and 95% CI). All statistical analyses were performed using Stata 17. RESULTS: We screened 3636 studies, but only 29 studies were included in the final review, of which 18 were included in the meta-analysis. The meta-analysis demonstrated that eHealth interventions improved moderate-to-vigorous intensity physical activity (standardized mean difference=0.18, 95% CI 0.07-0.28; P=.001) and vigorous-intensity physical activity (standardized mean difference=0.2, 95% CI 0.00-0.39; P=.048) but did not improve moderate-intensity physical activity (standardized mean difference=0.19, 95% CI -0.12 to 0.51; P=.23). No changes were observed in the cardiovascular-related outcomes. Post hoc subgroup analyses identified that wearable-based, web-based, and communication-based eHealth intervention delivery methods were effective. CONCLUSIONS: eHealth interventions are effective at increasing minutes per week of moderate-to-vigorous intensity physical activity among patients in cardiac rehabilitation. There was no difference in the effectiveness of the major eHealth intervention delivery methods, thereby providing evidence that in the future, health care professionals and researchers can personalize convenient and affordable interventions tailored to patient characteristics and needs to eliminate the inconvenience of visiting center-based cardiac rehabilitation programs during the COVID-19 pandemic and to provide better support for home-based maintenance of cardiac rehabilitation. TRIAL REGISTRATION: PROSPERO International Prospective Register of Systematic Reviews CRD42021278029; https://www.crd.york.ac.uk/prospero/display_record.php?RecordID=278029.

Excessive O-GlcNAcylation Causes Heart Failure and Sudden Death.

BACKGROUND: Heart failure is a leading cause of death worldwide and is associated with the rising prevalence of obesity, hypertension, and diabetes. O-GlcNAcylation (the attachment of O-linked ß-N-acetylglucosamine [O-GlcNAc] moieties to cytoplasmic, nuclear, and mitochondrial proteins) is a posttranslational modification of intracellular proteins and serves as a metabolic rheostat for cellular stress. Total levels of O-GlcNAcylation are determined by nutrient and metabolic flux, in addition to the net activity of 2 enzymes: O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA). Failing myocardium is marked by increased O-GlcNAcylation, but whether excessive O-GlcNAcylation contributes to cardiomyopathy and heart failure is unknown. METHODS: We developed 2 new transgenic mouse models with myocardial overexpression of OGT and OGA to control O-GlcNAcylation independent of pathologic stress. RESULTS: We found that OGT transgenic hearts showed increased O-GlcNAcylation and developed severe dilated cardiomyopathy, ventricular arrhythmias, and premature death. In contrast, OGA transgenic hearts had lower O-GlcNAcylation but identical cardiac function to wild-type littermate controls. OGA transgenic hearts were resistant to pathologic stress induced by pressure overload with attenuated myocardial O-GlcNAcylation levels after stress and decreased pathologic hypertrophy compared with wild-type controls. Interbreeding OGT with OGA transgenic mice rescued cardiomyopathy and premature death, despite persistent elevation of myocardial OGT. Transcriptomic and functional studies revealed disrupted mitochondrial energetics with impairment of complex I activity in hearts from OGT transgenic mice. Complex I activity was rescued by OGA transgenic interbreeding, suggesting an important role for mitochondrial complex I in O-GlcNAc-mediated cardiac pathology. CONCLUSIONS: Our data provide evidence that excessive O-GlcNAcylation causes cardiomyopathy, at least in part, attributable to defective energetics. Enhanced OGA activity is well tolerated and attenuation of O-GlcNAcylation is beneficial against pressure overload-induced pathologic remodeling and heart failure. These findings suggest that attenuation of excessive O-GlcNAcylation may represent a novel therapeutic approach for cardiomyopathy.

Evolved Biosensor with High Sensitivity and Specificity for Measuring Cadmium in Actual Environmental Samples.

Bacterial biosensors have great potential in contaminant detection for sensitivity, specificity, cost-effectiveness, and easy operation. However, the existing cadmium-responsive bacterial biosensors cannot meet the real-world detection requirements due to lack of sensitivity, specificity, and anti-interference capability. This study aimed to develop a bacterial biosensor for detecting the total and extractable cadmium in actual environmental samples. We constructed the cadmium-responsive biosensor with the regulatory element (cadmium resistance transcriptional regulatory, CadR) and the reporting element (GFP) and improved its performance by directed evolution. The mutant libraries of biosensors were generated by error-prone PCR and screened by continuous five-round fluorescence-activated cell sorting (FACS), and a bacteria variant epCadR5 with higher performance was finally isolated. Biosensor fluorescence intensity was measured by a microplate reader, and results showed that the evolved cadmium-responsive bacterial biosensor was of high sensitivity and specificity in detecting trace cadmium, with a detection limit of 0.45 µg/L, which is 6.8 times more specific to cadmium than that of the wild-type. Furthermore, microscopic qualitative analysis results showed that the bacteria could produce fluorescence response in a cadmium-contaminated soil matrix, and quantitative analysis results showed that the values of cadmium from epCadR5 bacteria were close to that from inductively coupled plasma-mass spectrometry. These results suggest that the biosensor may have a broad application prospect in the detection of cadmium-contaminated soil and water.

A Non-Cell-Autonomous Mode of DNA Damage Response in Soma of Caenorhabditis elegans.

Life has evolved a mechanism called DNA damage response (DDR) to sense, signal and remove/repair DNA damage, and its deficiency and dysfunction usually lead to genomic instability and development of cancer. The signaling mode of the DDR has been believed to be of cell-autonomy. However, the paradigm is being shifted with in-depth research into model organism Caenorhabditis elegans. Here, we mainly investigate the effect of DDR activation on the radiosensitivity of vulva of C. elegans, and first found that the vulval radiosensitivity is mainly regulated by somatic DDR, rather than the DDR of germline. Subsequently, the worm lines with pharynx-specific rescue of DDR were constructed, and it is shown that the 9-1-1-ATR and MRN-ATM cascades in pharynx restore approximately 90% and 70% of vulval radiosensitivity, respectively, through distantly regulating the NHEJ repair of vulval cells. The results suggest that the signaling cascade of DDR might also operate in a non-cell autonomous mode. To further explore the underlying regulatory mechanisms, the cpr-4 mutated gene is introduced into the DDR-rescued worms, and CPR-4, a cysteine protease cathepsin B, is confirmed to mediate the inter-tissue and inter-individual regulation of DDR as a signaling molecule downstream of 9-1-1-ATR. Our findings throw some light on the regulation of DNA repair in soma of C. elegans, and might also provide new cues for cancer prevention and treatment.

Prevalence and genetic characteristics of Cronobacter spp. from food and human clinical stool samples in Wenzhou, China 2008-2018.

Pathogenic Cronobacter species are responsible for life-threatening illness in neonates. A ten-year comprehensive survey was conducted to examine the population structure and antimicrobial resistant patterns of Cronobacter isolates from food (n = 78) and clinical (n = 12) sources in Wenzhou, China. A total of 90 (4.4%) isolates were recovered from 2051 collected samples. The occurrence of Cronobacter spp. was highest in spices with a rate of 22% (26/119), whereas the lowest contamination rate of 1% was found in powered infant and toddler formula (7/494), special medical infant formula (1/95) and human stool samples (12/1024). Cronobacter strains revealed a high degree of genetic diversity among the isolates tested. Pulsed-field gel electrophoresis (PFGE) distinguished 75 clonal groups, and the biggest cluster consisted of four strains. Multilocus sequence typing (MLST) method displayed 43 sequence types (STs), of which ST1, ST4, ST8, ST64, ST148 and ST201 were most frequently identified. Meanwhile, two new sequence types were discovered and added to the PubMLST international database. Resistance to ceftriaxone, cefotaxiv, amoxicillin, ampicillin, cefoxitin, tetracycline, streptomycin, azithromycin, chloramphenicol, as well as multidrug resistance, was noted. Taken together, this large-scale surveillance study highlights the wide dissemination and diverse molecular features of Cronobacter spp. in Wenzhou China.

A potential involvement of plant systemic response in initiating genotoxicity of Ag-nanoparticles in Arabidopsis thaliana.

The extensive availability of engineered nanomaterials in global markets has led to the release of substantial amounts of nanoparticles (NP) into atmosphere, water body and soil, yielding both beneficial and harmful effects in plant systems. The NP are mainly aggregated onto the surface of plant roots and leaves exposed and only slightly transported into other tissues with a low rate of internalization. This raises a question of whether plant systemic response is involved in the induction of biological effects of NP. To address this, model plant Arabidopsis thaliana were root exposed to low concentrations of Ag-NP of two particle sizes (10-nm and 60-nm), and expressions of homologous recombination (HR)-related genes and the alleviation of transcriptional gene silencing (TGS) in aerial leafy tissues were examined as genotoxic endpoints. Results showed that exposure of roots to two sizes of Ag-NP up-regulated expressions of HR genes, and reactivated TGS-silenced repetitive elements in aerial tissues. These effects were blocked by the impairment in the salicylic acid signal pathway, indicating a potential involvement of plant systemic response in the induction of Ag-NP genotoxicity. This is further supported by ICP-MS analysis, in which the Ag content in aerial tissues was not significantly changed by root exposure to 10-nm Ag-NP. Although a significant increase in the Ag content in aerial tissues was observed after root exposure to 60-nm Ag-NP, its genotoxic effects had no obvious difference from that by 10-nm Ag-NP exposure, also suggesting that the genotoxicity might be mainly induced via plant systemic response, at least in the experiments of root exposure to Ag-NP.

Differences in cadmium accumulation between indica and japonica rice cultivars in the reproductive stage.

Excessive cadmium (Cd) in rice grains is of great concern worldwide, particularly in southern China where heavy metal pollution in the soil is widespread. Much work has been done regarding the key genes responsible for Cd absorption, transport, and accumulation in rice, but little is known about the differences of Cd accumulation between indica and japonica rice cultivars during the reproductive stage. Furthermore, physiological parameters, such as nonstructural carbohydrate content, involved in Cd accumulation have not been fully elucidated. We studied several indica and japonica cultivars under three different Cd treatment levels and harvested them at different periods after heading. Differences in Cd accumulation between subspecies mainly were generated during the reproductive stage. An increase in the Cd pollution level caused the average absorption rate of Cd in the aerial parts of the indica cultivars in the reproductive stage to be 6.17, 4.52, and 3.89 times greater than that of the japonica cultivars across the three Cd treatments. The contribution of Cd absorption by shoots to Cd accumulation at the pre- or postheading stages was 33.8% and 66.2% in indica, and 44.9% and 55.1% in japonica. We found a significant negative correlation between Cd content in the rice grains and the content of nonstructural carbohydrates in the sheath (P < 0.05). Cd translocation from sheath to grain occurred along with sugar transfer in the indica cultivars. The Cd content of the indica cultivar grain was 1.84-4.14 times higher than that of the japonica cultivars (P < 0.05). The japonica cultivars thus met the cereal Cd limits of China (0.2 mg kg-1) under low and moderate soil Cd pollution. These findings are helpful for the selection of proper cultivars and field management practices to alleviate Cd exposure risk in rice production.

GC⁻MS-Based Nontargeted and Targeted Metabolic Profiling Identifies Changes in the Lentinula edodes Mycelial Metabolome under High-Temperature Stress.

To clarify the physiological mechanism of the Lentinula edodes (L. edodes) response to high-temperature stress, two strains of L. edodes with different tolerances were tested at different durations of high temperature, and the results showed that there were significant changes in their phenotypes and physiology. To further explore the response mechanism, we established a targeted GC-MS-based metabolomics workflow comprising a standardized experimental setup for growth, treatment and sampling of L. edodes mycelia, and subsequent GC-MS analysis followed by data processing and evaluation of quality control (QC) measures using tailored statistical and bioinformatic tools. This study identified changes in the L. edodes mycelial metabolome following different time treatments at high temperature based on nontargeted metabolites with GC-MS and further adopted targeted metabolomics to verify the results of the analysis. After multiple statistical analyses were carried out using SIMCA software, 74 and 108 differential metabolites were obtained, respectively. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis showed that the metabolic pathways with significant changes included those related to the following: amino acid metabolism, the glycolysis pathway, the tricarboxylic acid (TCA) cycle, and sugar metabolism. Most amino acids and carbohydrates enriched in these metabolic pathways were upregulated in strain 18, downregulated in strain 18N44, or the synthesis in strain 18 was higher than that in strain 18N44. This result was consistent with the physiological phenotypic characteristics of the two strains under high-temperature stress and revealed the reason why strain 18N44 was more heat-sensitive. At the same time, under high temperature, the decrease of intermediate products in glycolysis and the TCA cycle resulted in carbon starvation and insufficient energy metabolism, thus inhibiting the growth of L. edodes. In addition, the results also showed that the metabolites produced by different L. edodes strains under high-temperature stress were basically the same. However, different strains had species specificity, so the changes in the content of metabolites involved in the response to high-temperature stress were different. This provides a theoretical basis for further understanding the mechanism of the L. edodes response to high temperature and can be used to establish an evaluation system of high-temperature-resistant strains and lay the foundation for molecular breeding of new L. edodes strains resistant to high temperature.

Inhibition of MCU forces extramitochondrial adaptations governing physiological and pathological stress responses in heart.

Myocardial mitochondrial Ca(2+) entry enables physiological stress responses but in excess promotes injury and death. However, tissue-specific in vivo systems for testing the role of mitochondrial Ca(2+) are lacking. We developed a mouse model with myocardial delimited transgenic expression of a dominant negative (DN) form of the mitochondrial Ca(2+) uniporter (MCU). DN-MCU mice lack MCU-mediated mitochondrial Ca(2+) entry in myocardium, but, surprisingly, isolated perfused hearts exhibited higher O2 consumption rates (OCR) and impaired pacing induced mechanical performance compared with wild-type (WT) littermate controls. In contrast, OCR in DN-MCU-permeabilized myocardial fibers or isolated mitochondria in low Ca(2+) were not increased compared with WT, suggesting that DN-MCU expression increased OCR by enhanced energetic demands related to extramitochondrial Ca(2+) homeostasis. Consistent with this, we found that DN-MCU ventricular cardiomyocytes exhibited elevated cytoplasmic [Ca(2+)] that was partially reversed by ATP dialysis, suggesting that metabolic defects arising from loss of MCU function impaired physiological intracellular Ca(2+) homeostasis. Mitochondrial Ca(2+) overload is thought to dissipate the inner mitochondrial membrane potential (ΔΨm) and enhance formation of reactive oxygen species (ROS) as a consequence of ischemia-reperfusion injury. Our data show that DN-MCU hearts had preserved ΔΨm and reduced ROS during ischemia reperfusion but were not protected from myocardial death compared with WT. Taken together, our findings show that chronic myocardial MCU inhibition leads to previously unanticipated compensatory changes that affect cytoplasmic Ca(2+) homeostasis, reprogram transcription, increase OCR, reduce performance, and prevent anticipated therapeutic responses to ischemia-reperfusion injury.

CEF1/OsMYB103L is involved in GA-mediated regulation of secondary wall biosynthesis in rice.

Although the main genes in rice involved in the biosynthesis of secondary wall components have been characterized, the molecular mechanism underlying coordinated regulation of genes expression is not clear. In this study, we reported a new rice variety, cef1, showed the culm easily fragile (CEF) without other concomitant phenotypes. The CEF1 gene encodes a MYB family transcription factor OsMYB103L, was cloned based on map-based approach. Bioinformatics analyses indicated that CEF1 belongs to the R2R3-MYB subfamily and highly similar to Arabidopsis AtMYB103. Expression pattern analysis indicated that CEF1 is mainly expressed in internodes and panicles. Biochemical assays demonstrated that OsMYB103L is a nuclear protein and shows high transcriptional activation activity at C-terminus. OsMYB103L mediates cellulose biosynthesis and secondary walls formation mainly through directly binding the CESA4, CESA7, CESA9 and BC1 promoters and regulating their expression. OsMYB103L may also function as a master switch to regulate the expression of several downstream TFs, which involved in secondary cell wall biosynthesis. Furthermore, OsMYB103L physically interacts with SLENDER RICE1 (SLR1), a DELLA repressor of GA signaling, and involved in GA-mediated regulation of cellulose synthesis pathway. Our findings revealed that OsMYB103L plays an important role in GA-regulating secondary cell wall synthesis, and the manipulation of this gene provide a new strategy to help the straw decay in soil.

Genetic inhibition of Na+-Ca2+ exchanger current disables fight or flight sinoatrial node activity without affecting resting heart rate.

RATIONALE: The sodium-calcium exchanger 1 (NCX1) is predominantly expressed in the heart and is implicated in controlling automaticity in isolated sinoatrial node (SAN) pacemaker cells, but the potential role of NCX1 in determining heart rate in vivo is unknown. OBJECTIVE: To determine the role of Ncx1 in heart rate. METHODS AND RESULTS: We used global myocardial and SAN-targeted conditional Ncx1 knockout (Ncx1(-/-)) mice to measure the effect of the NCX current on pacemaking activity in vivo, ex vivo, and in isolated SAN cells. We induced conditional Ncx1(-/-) using a Cre/loxP system. Unexpectedly, in vivo and ex vivo hearts and isolated SAN cells showed that basal rates in Ncx1(-/-) (retaining ≈20% of control level NCX current) and control mice were similar, suggesting that physiological NCX1 expression is not required for determining resting heart rate. However, increases in heart rate and SAN cell automaticity in response to isoproterenol or the dihydropyridine Ca(2+) channel agonist BayK8644 were significantly blunted or eliminated in Ncx1(-/-) mice, indicating that NCX1 is important for fight or flight heart rate responses. In contrast, the pacemaker current and L-type Ca(2+) currents were equivalent in control and Ncx1(-/-) SAN cells under resting and isoproterenol-stimulated conditions. Ivabradine, a pacemaker current antagonist with clinical efficacy, reduced basal SAN cell automaticity similarly in control and Ncx1(-/-) mice. However, ivabradine decreased automaticity in SAN cells isolated from Ncx1(-/-) mice more effectively than in control SAN cells after isoproterenol, suggesting that the importance of NCX current in fight or flight rate increases is enhanced after pacemaker current inhibition. CONCLUSIONS: Physiological Ncx1 expression is required for increasing sinus rates in vivo, ex vivo, and in isolated SAN cells, but not for maintaining resting heart rate.

BK channels regulate sinoatrial node firing rate and cardiac pacing in vivo.

Large-conductance Ca(2+)- and voltage-activated K(+) (BK) channels play prominent roles in shaping muscle and neuronal excitability. In the cardiovascular system, BK channels promote vascular relaxation and protect against ischemic injury. Recently, inhibition of BK channels has been shown to lower heart rate in intact rodents and isolated hearts, suggesting a novel role in heart function. However, the underlying mechanism is unclear. In the present study, we recorded ECGs from mice injected with paxilline (PAX), a membrane-permeable BK channel antagonist, and examined changes in cardiac conduction. ECGs revealed a 19 ± 4% PAX-induced reduction in heart rate in wild-type but not BK channel knockout (Kcnma1(-/-)) mice. The heart rate decrease was associated with slowed cardiac pacing due to elongation of the sinus interval. Action potential firing recorded from isolated sinoatrial node cells (SANCs) was reduced by 55 ± 15% and 28 ± 9% by application of PAX (3 µM) and iberiotoxin (230 nM), respectively. Furthermore, baseline firing rates from Kcnma1(-/-) SANCs were 33% lower than wild-type SANCs. The slowed firing upon BK current inhibition or genetic deletion was due to lengthening of the diastolic depolarization phase of the SANC action potential. Finally, BK channel immunoreactivity and PAX-sensitive currents were identified in SANCs with HCN4 expression and pacemaker current, respectively, and BK channels cloned from SANCs recapitulated similar activation as the PAX-sensitive current. Together, these data localize BK channels to SANCs and demonstrate that loss of BK current decreases SANC automaticity, consistent with slowed sinus pacing after PAX injection in vivo. Furthermore, these findings suggest BK channels are potential therapeutic targets for disorders of heart rate.

Characterization and mapping of a spotted leaf mutant in rice (Oryza sativa).

Spotted leaf mutant belongs to a class of mutants that can produce necrotic lesions spontaneously in plants without any attack by pathogens. These mutants have no beneficial effect on plant productivity but provide a unique opportunity to study programmed cell death in plant defense responses. A novel rice spotted leaf mutant (spl30) was isolated through low-energy heavy ion irradiation. Lesion expression was sensitive to light and humidity. The spl30 mutant caused a decrease in chlorophyll and soluble protein content, with marked accumulation of reactive oxygen species (ROS) around the lesions. In addition, the spl30 mutant significantly enhanced resistance to rice bacterial blight (X. oryzae pv. oryzae) from China (C1-C7). The use of SSR markers showed that the spl30 gene was located between markers XSN2 and XSN4. The genetic distance between the spl30 gene and XSN2 and between spl30 and XSN4 was 1.7 cM and 0.2 cM, respectively. The spl30 gene is a new gene involved in lesion production and may be related to programmed cell death in rice. The ability of this mutant to confer broad resistance to bacterial blight provides a model for studying the interaction between plants and pathogenic bacteria.