Association of physical activity and air pollution exposure with the risk of type 2 diabetes: a large population-based prospective cohort study.

BACKGROUND: The interplay between physical activity (PA) and air pollution in relation to type 2 diabetes (T2D) remains largely unknown. Based on a large population-based cohort study, this study aimed to examine whether the benefits of PA with respect to the risk of T2D are moderated by exposure to air pollution. METHODS: UK Biobank participants (n = 359,153) without diabetes at baseline were included. Information on PA was obtained using the International Physical Activity Questionnaire short form. Exposure to air pollution, including PM2.5, PMcoarse (PM2.5-10), PM10, and NO2, was estimated from land use regression models. Cox regression models were used to estimate the hazard ratios (HRs) and 95% confidence intervals (95% CIs). RESULTS: During a median of 8.9 years of follow-up, 13,706 T2D events were recorded. Compared with a low PA level, the HRs for the risk of T2D among individuals with moderate and high PA were 0.82 (95% CI, 0.79-0.86) and 0.73 (95% CI, 0.70-0.77), respectively. Compared with low levels of air pollution, the HRs for risk of T2D for high levels of air pollution (PM2.5, PMcoarse, PM10, and NO2) were 1.19 (1.14-1.24), 1.06 (1.02-1.11), 1.13 (1.08-1.18), and 1.19 (1.14-1.24), respectively. There was no effect modification of the associations between PA and T2D by air pollution (all P-interactions > 0.05). The inverse associations between PA and T2D in each air pollution stratum were generally consistent (all P for trend < 0.05). CONCLUSION: A higher PA and lower air pollution level were independently associated with a lower risk of T2D. The beneficial effects of PA on T2D generally remained stable among participants exposed to different levels of air pollution. Further studies are needed to replicate our findings in moderately and severely polluted areas.

Associations Between High-Sensitivity C-Reactive Protein and All-Cause Mortality Among Oldest-Old in Chinese Longevity Areas: A Community-Based Cohort Study.

BACKGROUND: The association between high-sensitivity C-reactive protein (hsCRP) levels and all-cause mortality for the oldest-old (aged 80 years or older) remains unclear. We aimed to investigate the associations between hsCRP concentrations and the risks of all-cause mortality, and further identify the potential modifying factors affecting these associations among the oldest-old. METHODS: This prospective, community-based cohort study included 2,206 participants aged 80 years or older (median age 93.0 years) from the Healthy Aging and Biomarkers Cohort Study. Cox proportional hazards regression models were used to estimate hazard ratios (HRs) with 95% confidential intervals (95% CIs) for all-cause mortality according to hsCRP quartiles and recommendation for relative risk categories of hsCRP levels (< 1.0, 1.0-3.0, and > 3.0 mg/L), with adjustment for sociodemographic information, lifestyle, physical examination, medical history, and other potential confounders. RESULTS: During a median follow-up period of 3.1 years (IQR: 1.6-3.9 years), 1,106 deaths were verified. After full adjustment for potential confounders, a higher hsCRP concentration was positively associated with an increased risk of all-cause mortality (P for trend < 0.001). Compared with the lowest quartile, the fully adjusted HRs of the second, third, and fourth quartiles were 1.17 (95% CI: 0.94, 1.46), 1.28 (95% CI: 1.01, 1.61), and 1.49 (95% CI: 1.20, 1.87), respectively. The association of hsCRP with all-cause mortality was modified by smoking status (P for interaction = 0.011), an increased risk of hsCRP with all-cause mortality showed among non-current smokers (HR: 1.17; 95% CI: 1.07, 1.28), but no significance was observed in current smokers (HR: 0.83; 95% CI: 0.66, 1.18). CONCLUSIONS: Our study indicated that elevated hsCRP concentrations were associated with a higher risk of all-cause mortality among Chinese oldest-old. Future studies investigating additional factors of disease and aging processes are needed to obtain a better understanding of the mechanisms.

Tooth Loss, Denture Use, and Cognitive Impairment in Chinese Older Adults: A Community Cohort Study.

BACKGROUND: Evidence regarding the associations of tooth loss and denture use with incident cognitive impairment is inconclusive in older adults, and few prospective studies have examined the potential interaction between tooth loss and denture use in these specific populations. METHODS: Data were assessed from 17 079 cognitively normal older adults aged ≥65 years, participating in the Chinese Longitudinal Healthy Longevity Survey. The outcome of interest was cognitive impairment (assessed by the Chinese version of Mini-Mental State Examination). The number of natural teeth and status of denture use were collected by a structural questionnaire. RESULTS: A total of 6456 cases of cognitive impairment were recorded during 88 627 person-years of follow-up. We found that compared with participants with 20+ teeth, those with 10-19, 1-9, and 0 teeth had increased risks of incident cognitive impairment (p-trend < .001). Participants without dentures also had a higher risk of incident cognitive impairment, compared with those who wore dentures. Effect modification by denture use was observed (p-interaction = .010). Specifically, among those without dentures, the adjusted hazard ratio (95% confidence interval) for participants with 10-19, 1-9, and 0 teeth were 1.19 (1.08, 1.30), 1.28 (1.17, 1.39), and 1.28 (1.16, 1.41), respectively, as compared to those with 20+ teeth. In contrary, among denture users, detrimental effect was only observed among those with 0 teeth (hazard ratio 1.14, 95% confidence interval: 1.16, 1.41). CONCLUSIONS: In Chinese older adults, maintaining 20+ teeth is important for cognitive health; denture use would attenuate the detrimental effects of tooth loss, especially for partial tooth loss, on cognitive impairment.

Healthy Sleep Associated With Lower Risk of Hypertension Regardless of Genetic Risk: A Population-Based Cohort Study.

Background: Hypertension is a leading contributor to the global burden of disease and to mortality. The combined effects of sleep factors on the risk of hypertension are unclear. We aimed to evaluate the effect of combined sleep factors on the risk of hypertension and to explore whether this association is independent of genetic risk. Methods: This population-based prospective cohort study included 170,378 participants from the UK Biobank study. We conducted a healthy sleep score based on a combination of major five sleep factors and a genetic risk score based on 118 risk variants. Cox proportional hazard regression models were used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs). Results: A total of 170,378 participants were included. Compared to participants with a healthy sleep score of 0-1, those with healthy sleep scores of 2 (HR, 0.90; 95% CI, 0.83-0.98), 3 (HR, 0.81; 95% CI, 0.75-0.88), 4 (HR, 0.74; 95% CI, 0.68-0.81), or 5 (HR, 0.67; 95% CI, 0.59-0.77) had increasingly lower risks of hypertension (P for trend <0.001). Participants with high genetic risk and an unfavorable sleep pattern had a 1.80-fold greater risk of hypertension than participants with low genetic risk and a favorable sleep pattern. The association between sleep patterns and hypertension persisted in subgroup analysis, stratified by the genetic risk. Nearly 18.2% of hypertension events in this cohort could be attributed to unfavorable sleep pattern. Conclusions: Favorable sleep pattern was associated with a low risk of hypertension, regardless of genetic risk. These findings highlight the potential of sleep interventions to reduce risk of hypertension across entire populations.

Influence of Diabetes Duration and Glycemic Control on Dementia: A Cohort Study.

BACKGROUND: To investigate the influence of diabetes duration and glycemic control, assessed by glycated hemoglobin (HbA1c) levels, on risk of incident dementia. METHODS: The present study is a prospective study of 461 563 participants from the UK Biobank. The age at diabetes diagnosis was determined by self-report. Diabetes duration was calculated as baseline age minus age at diagnosis. Cox proportional hazards regression models were used to estimate hazard ratios (HRs) with 95% confidential intervals (CIs). RESULTS: During a median follow-up of 8.1 years, 2 233 dementia cases were recorded. As compared with normoglycemic individuals, individuals with diabetes had higher risk of all-cause dementia, and the risk increased with increasing duration of diabetes; compared with participants with diabetes duration of <5 years, the multivariable-adjusted HRs (95% CIs) were 1.49 (1.12-1.97), 1.71 (1.21-2.41), and 2.15 (1.60-2.90) for those with diabetes durations ≥5 to < 10, ≥10 to <15, and ≥ 15 years, respectively (p for trend < .001). Among participants with diabetes, those with both longer diabetes duration (diabetes duration ≥ 10 years) and poor glycemic control (HbA1c ≥ 8%) had the highest risk of all-cause dementia (multivariable-adjusted HR = 2.07, 95% CI 1.45, 2.94), compared with patients with shorter duration of diabetes and better glycemic control (diabetes duration < 10 years and HbA1c < 8%). CONCLUSIONS: Diabetes duration appeared to be associated with the risk of incident dementia due to factors beyond glycemic control. Clinicians should consider not only glycemic control but also diabetes duration in dementia risk assessments for patients with diabetes.

Depression as a Mediator of the Association Between Wealth Status and Risk of Cognitive Impairment and Dementia: A Longitudinal Population-Based Cohort Study.

BACKGROUND: Wealth and income are potential modifiable risk factors for dementia, but whether wealth status, which is composed of a combination of debt and poverty, and assessed by wealth and income, is associated with cognitive impairment among elderly adults remains unknown. OBJECTIVE: To examine the associations of different combinations of debt and poverty with the incidence of dementia and cognitive impairment without dementia (CIND) and to evaluate the mediating role of depression in these relationships. METHODS: We included 15,565 participants aged 51 years or older from the Health and Retirement Study (1992-2012) who were free of CIND and dementia at baseline. Dementia and CIND were assessed using either the modified Telephone Interview for Cognitive Status (mTICS) or a proxy assessment. Cox models with time-dependent covariates and mediation analysis were used. RESULTS: During a median of 14.4 years of follow-up, 4,484 participants experienced CIND and 1,774 were diagnosed with dementia. Both debt and poverty were independently associated with increased dementia and CIND risks, and the risks were augmented when both debt and poverty were present together (the hazard ratios [95% confidence intervals] were 1.35 [1.08-1.70] and 1.96 [1.48-2.60] for CIND and dementia, respectively). The associations between different wealth statuses and cognition were partially (mediation ratio range: 11.8-29.7%) mediated by depression. CONCLUSION: Debt and poverty were associated with an increased risk of dementia and CIND, and these associations were partially mediated by depression. Alleviating poverty and debt may be effective for improving mental health and therefore curbing the risk of cognitive impairment and dementia.

Diabetes duration and glycaemic control as predictors of cardiovascular disease and mortality.

AIMS: To assess the associations of diabetes duration and glycaemic control (defined by plasma glycated haemoglobin [HbA1c] level) with the risks of cardiovascular disease (CVD) and all-cause mortality and to determine whether the addition of either or both to the established CVD risk factors can improve predictions. MATERIALS AND METHODS: A total of 435 679 participants from the UK Biobank without CVD at baseline were included. Cox models adjusting for classic risk factors (sociodemographic and anthropometric characteristics, lipid profiles and medication use) were used, and predictive utility was determined by the C-index and net reclassification improvement (NRI). RESULTS: Compared with participants without diabetes, participants with longer diabetes durations and poorer glycaemic control had a higher risk of fatal/nonfatal CVD. Among participants with diabetes, the fully-adjusted hazard ratios (HRs) for diabetes durations of 5 to <10 years, 10 to <15 years and ≥15 years were 1.15 (95% confidence interval [CI] 0.99, 1.34), 1.50 (95% CI 1.26, 1.79) and 2.22 (95% CI 1.90, 2.58; P-trend <0.01), respectively, compared with participants with diabetes durations <5 years. In addition, those with the longest disease duration (≥15 years) and poorer glycaemic control (HbA1c ≥64 mmol/mol [8%]) had the highest risk of fatal/nonfatal CVD (HR 3.12, 95% CI 2.52, 3.86). Among participants with diabetes, the addition of both diabetes duration and glycaemic control levels significantly improved both the C-index (change in C-index +0.0254; 95% CI 0.0111, 0.0398) and the overall NRI for fatal/nonfatal CVD (0.0992; 95% CI 0.0085, 0.1755) beyond the use of the classic risk factors. CONCLUSIONS: Both longer diabetes duration and poorer glycaemic control were associated with elevated risks of CVD and mortality. Clinicians should consider not only glycaemic control but also diabetes duration in CVD risk assessments for participants with diabetes.

Isolated systolic and diastolic hypertension by the 2017 American College of Cardiology/American Heart Association guidelines and risk of cardiovascular disease: a large prospective cohort study.

OBJECTIVE: The 2017 American College of Cardiology/American Heart Association blood pressure (BP) guidelines lowered the hypertension threshold from a SBP/DBP level of at least 140/90 mmHg to at least 130/80 mmHg. The cardiovascular impact of isolated systolic hypertension (ISH) and isolated diastolic hypertension (IDH) under the new definition remains unclear. METHODS: We used data from the UK Biobank study, which is a prospective population-based cohort study. Participants were categorized into five groups: normal BP, normal high BP, ISH, IDH and systolic and diastolic hypertension. The primary endpoint for this study was the composite of nonfatal myocardial infarction (MI), nonfatal ischaemic stroke, nonfatal haemorrhagic stroke and cardiovascular disease (CVD) death. We also explored the results for the above-mentioned CVD outcomes separately. Baseline BP measurements were obtained twice after the participant had been at rest for at least 5 min in a seated position. RESULTS: We included 385 955 participants who were not taking antihypertensive medications, were free of CVD at baseline and had available data on BP measurements. During a median follow-up of 8.1 years, 8959 CVD events were recorded, including 4729 nonfatal MIs, 2287 nonfatal ischaemic strokes, 813 nonfatal haemorrhagic strokes, and 1826 CVD deaths. According to the hypertension threshold of at least 130/80 mmHg by the American College of Cardiology/American Heart Association guidelines, both ISH (hazard ratio 1.39; 95% confidence interval 1.27, 1.15) and IDH (hazard ratio 1.28; 95% confidence interval 1.15, 1.43) were significantly associated with a higher overall CVD risk than normal BP. ISH was associated with most CVD risk, except for ischaemic stroke, while the excess CVD risk associated with IDH appeared to be driven mainly by MI and CVD death. We found heterogeneity by sex and age regarding the effects of IDH on overall CVD risk, with significant associations in younger adults (age <60 years) and women and null associations in men and older adults (age ≥60 years). CONCLUSION: ISH was associated with the risk of most CVD events, while the association between IDH and CVD risk was mainly driven by MI incidence and CVD death. Further research is needed to identify participants with IDH who have a particular risk for developing CVD.

Association Between Plasma 25-hydroxyvitamin D Concentrations and Incident Activities of Daily Living Disability: A Longitudinal Community-Based Cohort Study.

OBJECTIVES: A few studies of Western populations have found inconsistent results regarding the associations between vitamin D status and physical function. We explored the association between circulating vitamin D status [plasma 25-hydroxyvitamin D, 25(OH)D] and incident activities of daily living (ADL) disability among Chinese older adults. DESIGN: Community-based longitudinal cohort study. SETTING AND PARTICIPANTS: A total of 2453 men and women (median age 84.0 years) in 7 Chinese longevity areas were included. MEASURES: Cox proportional hazards regression models were used to estimate hazard ratios (HRs) with 95% confidence intervals (CIs) for incident ADL, with adjustments for potential sociodemographic, and lifestyle confounders and biomarkers. Because there was a statistically significant interaction between plasma 25(OH)D and sex in relation to incident ADL, men and women were analyzed separately. RESULTS: The median concentrations of plasma 25(OH)D were 46.6 nmol/L and 36.4 nmol/L for men and women, respectively. Compared with the lowest quartile in the fully adjusted model, the HR for incident ADL disability for the highest quartile was 0.55 (95% CI 0.36-0.85) for women; for men, a null association was indicated (HRhighest vs lowest 0.61, 95% CI 0.37-1.00). However, when using the recommended circulating 25(OH)D thresholds by the US Institute of Medicine, those with vitamin D sufficiency (≥50 nmol/L) had better ADL disability prognoses than those with vitamin D deficiency (<30 nmol/L) in both sexes (men HR 0.45, 95% CI 0.28-0.72; women HR 0.58, 95% CI 0.37-0.90). CONCLUSIONS AND IMPLICATIONS: The relationship between plasma 25(OH)D concentration and incident ADL disability was sex-specific among Chinese older adults. However, participants with recommended vitamin D sufficiency may have better disability prognoses in both sexes, suggesting that the recommended 25(OH)D concentration for bone health may extend to functional outcomes such as ADL disability in Chinese older adults.

Prevalence of anxiety and depression symptom, and the demands for psychological knowledge and interventions in college students during COVID-19 epidemic: A large cross-sectional study.

BACKGROUND: Although studies have suggested experiencing the epidemic of severe infectious diseases increased the prevalence of mental health problems, the association between COVID-19 epidemic and risk of anxiety and depression symptom in college students in China was unclear. METHODS: A large cross-sectional online survey with 44,447 college students was conducted in Guangzhou, China. The Zung's Self-rating Anxiety Scale (SAS) and the Center for Epidemiologic Studies Depression Scale (CES-D Scale) were used to define the anxiety and depression symptom, respectively. Multivariable logistic regression models were used to analyze the association between COVID-19 epidemic and risk of anxiety and depression symptom. RESULTS: The prevalence of anxiety and depression symptom was 7.7% (95% confidence interval [CI]: 7.5%, 8.0%) and 12.2% (95%CI: 11.9%, 12.5%), respectively. Compared with students who reported have not infected or suspected cases in family members and relatives, students who reported having confirmed (OR=4.06; 95%CI: 1.62, 10.19; P = 0.003), and suspected (OR=2.11; 95%CI: 1.11, 4.00; P = 0.023) cases in family members and relatives had higher risk of depression symptom. Additionally, the proportions of students with anxiety and depression symptom reported more demand of psychological knowledge and interventions than those without (P<0.001). LIMITATIONS: All the data in this study was collected through online questionnaire, and we did not evaluate the reliability and validity. CONCLUSIONS: The prevalence of anxiety and depression symptom was relatively low in college students, but the COVID-19 epidemic-related factors might be associated with higher depression symptom risk.

Functionalized Reduced Graphene Oxide Loaded Aligned Carbon Nanotube Layer Used as Counter Electrode for Dye-Sensitized Solar Cells.

A novel bilayer counter electrodes for Dye-sensitized Solar Cells (DSSCs) made of reduced graphene oxide (RGO) and aligned carbon nanotube (ACNT) was developed. The underlayer ACNT severs as a transition layer for RGO. The overlayer of RGO plays the role of catalytic layer. It was demonstrated that the property of graphene counter electrode was adversely affected by aggregation, by adding surfactant, the aggregation of graphene can be inhabited effectively. Moreover, the interface between the RGO and the ACNT can be optimized by surfactant functionalization of RGO. After screening, a cationic surfactant cetylpyridinium chloride (CPC) functionalized RGO, code as CPC-RGO, exhibits the best performance. Compare to the ACNT based counter electrode and other surfactant functionalized RGO/ACNT based bilayer counter electrodes, the CPC-RGO/ACNT reduced interface resistance and improved the double chemical capacitance efficiently, thus uplifting the short circuit current density and fill factor from 7.35 to 8.8 mA cm-2, and 59.87 to 62.79, respectively. Eventually, the CPC-RGO/ACNT based DSSC giving a power conversion efficiency of 3.9%, which is 1.24-fold than that of ANCT based DSSC, because of the best splay degree of CPC/RGO.

MAPK-like protein 1 positively regulates maize seedling drought sensitivity by suppressing ABA biosynthesis.

Mitogen-activated protein kinase (MAPK) cascades play vital roles in regulating plant growth, development, and stress responses. MAPK-like (MPKL) proteins are a group of kinases containing the MAPK signature TxY motif and showing sequence similarity to MAPKs. However, the functions of plant MPKL proteins are currently unknown. The maize (Zea mays) genome contains four genes encoding MPKL proteins, here named ZmMPKL1 to ZmMPKL4. In this study, we show that ZmMPKL1 possesses kinase activity and that drought-induced ZmMPKL1 expression, ZmMPKL1 overexpression and knockout maize seedlings exhibited no visible morphological difference from wild-type B73 seedlings when grown under normal conditions. By contrast, under drought conditions, ZmMPKL1-overexpressing seedlings showed increased stomatal aperture, water loss, and leaf wilting and knockout seedlings showed the opposite phenotypes. Moreover, these drought-sensitive phenotypes in ZmMPKL1-overexpressing seedlings were restored by exogenous abscisic acid (ABA). ZmMPKL1 overexpression reduced drought-induced ABA production in seedlings and the knockout showed enhanced ABA production. Drought-induced transcription of ABA biosynthetic genes were suppressed and ABA catabolic genes were enhanced in ZmMPKL1-overexpressing seedlings, while their transcription were reversely regulated in knockout seedlings. These results suggest that ZmMPKL1 positively regulates seedlings drought sensitivity by altering the transcription of ABA biosynthetic and catabolic genes, and ABA homeostasis.

The RAF-like mitogen-activated protein kinase kinase kinases RAF22 and RAF28 are required for the regulation of embryogenesis in Arabidopsis.

In Arabidopsis, embryonic development follows a stereotypical pattern of cell division. Although many factors have been reported to participate in establishment of the proper embryonic pattern, the molecular mechanisms underlying pattern formation are unclear. In this study we showed that RAF22 and RAF28, two RAF-like mitogen-activated protein kinase kinase kinases (MAPKKKs) in Arabidopsis, are involved in the regulation of embryogenesis. The double knockout mutant of RAF22 and RAF28 was embryo lethal. A large proportion of the raf22-/- raf28+/- mutant embryos exhibited various defects, including disordered proembryo cell divisions, disruption of the bilaterally symmetrical structure, abnormally formative divisions of hypophysis and exaggerated suspensor growth. Whereas the kinase active form of RAF22 could complement these embryonic aberrant phenotypes, the kinase inactive form could not. The restrictive expression of the basal cell fate marker WOX8 in the abnormally dividing suspensor cells and the apical cell linage marker WOX2 in the abnormal proembryos indicated that apical and basal cell fates were unchanged in the abnormal embryos. The polar distribution of the auxin maxima and the PIN1 and PIN7 auxin transporters was markedly altered in the abnormal embryos. Our results suggest that RAF22 and RAF28 are important components of embryogenesis and that auxin polar transport may be involved in this regulation.

One-step synthesis of SnO hierarchical architectures under room temperature and their photocatalytic properties.

Three-dimensional (3D) SnO hierarchical architectures were synthesized via a one-step dissolution-precipitation route under room temperature using SnCl2 · 2H2O and Na2CO3 as the initial reagents. The morphology and size of the prepared SnO structures could be easily tailored by alternating the solvent from deionized water with absolute ethanol. The SEM observation showed that the prepared 3D SnO hierarchical architectures consisted of nanosheets. The size of the SnO hierarchical architectures could be effectively reduced from 4-10 µm to 1-2 µm when the solvent was changed from water to ethanol while the thickness of the assembling nanosheets was reduced from 200-500 nm to 20-30 nm at the same time. The possible formation mechanism of the 3D SnO hierarchical architectures is proposed in this paper. The photodegradation of methylene blue revealed that the SnO hierarchical structures prepared using ethanol as the solvent exhibit much better photocatalytic activity due to its smaller particle size, larger specific surface area, and appropriate band structure as well.

Arabidopsis MKK10-MPK6 mediates red-light-regulated opening of seedling cotyledons through phosphorylation of PIF3.

Photomorphogenesis is an important process in which seedlings emerge from soil and begin autotrophic growth. Mechanisms of photomorphogenesis include light signal perception, signal transduction, and the modulation of expression of light-responsive genes, ultimately leading to cellular and developmental changes. Phytochrome-interacting factors (PIFs) play negative regulatory roles in photomorphogenesis. Light-induced activation of phytochromes triggers rapid phosphorylation and degradation of PIFs, but the kinases responsible for the phosphorylation of PIFs are largely unknown. Here, we show that Arabidopsis MPK6 is a kinase involved in phosphorylating PIF3 and regulating red light-induced cotyledon opening, a crucial process during seedling photomorphogenesis. MPK6 was activated by red light, and the cotyledon opening angle in red light was reduced in mpk6 seedlings. MKK10, a MAPKK whose function is currently unclear, appears to act as a kinase upstream of MPK6 in regulating cotyledon opening. Activation of MPK6 by MKK10 led to the phosphorylation of PIF3 and accelerated its turnover in transgenic seedlings. Accordingly, the overexpression of PIF3 suppressed MKK10-induced cotyledon opening. MKK10 and MPK6 function downstream of phyB in regulating seedling cotyledon opening in red light. Therefore, the MKK10-MPK6 cascade appears to mediate the regulation of red-light-controlled seedling photomorphogenesis via a mechanism that might involve the phosphorylation of PIF3.

Activation of ZmMKK10, a maize mitogen-activated protein kinase kinase, induces ethylene-dependent cell death.

Mitogen-activated protein kinase (MAPK) cascades play important roles in regulating plant growth, development and stress responses. Here, we report that ZmMKK10, a maize MAP kinase kinase, positively regulates cell death. Sequence comparison to Arabidopsis MKKs has led to ZmMKK10 being classified as a group D MKK. Kinase activity analysis of recombinant ZmMKK10 showed that the Mg2+ ion was required for its kinase activity. Transient expression of ZmMKK10WT or ZmMKK10DD (the active form of ZmMKK10) in maize mesophyll protoplast significantly increased the cell death rate. Inducible expression of ZmMKK10WT or ZmMKK10DD in Arabidopsis transgenic plants caused rapid HR-like cell death, whereas induction of ZmMKK10KR (the inactive form of ZmMKK10) expression in transgenic plants did not yield the same phenotype. Genetic and pharmacological analysis revealed that ZmMKK10-induced cell death in transgenic plants requires the activation of Arabidopsis MPK3 and MPK6 and that it partially depended on ethylene biosynthesis. ZmMPK3 and ZmMPK7, the orthologues of Arabidopsis MPK3 and MPK6, interacted with ZmMKK10 in yeast and ZmMKK10 phosphorylated them both in vitro. Our results demonstrate that ZmMKK10 induces cell death in an ethylene-dependent manner. Furthermore, ZmMPK3 and ZmMPK7 may be the downstream MAPKs in this process.

A re-evaluation of the final step of vanillin biosynthesis in the orchid Vanilla planifolia.

A recent publication describes an enzyme from the vanilla orchid Vanilla planifolia with the ability to convert ferulic acid directly to vanillin. The authors propose that this represents the final step in the biosynthesis of vanillin, which is then converted to its storage form, glucovanillin, by glycosylation. The existence of such a "vanillin synthase" could enable biotechnological production of vanillin from ferulic acid using a "natural" vanilla enzyme. The proposed vanillin synthase exhibits high identity to cysteine proteases, and is identical at the protein sequence level to a protein identified in 2003 as being associated with the conversion of 4-coumaric acid to 4-hydroxybenzaldehyde. We here demonstrate that the recombinant cysteine protease-like protein, whether expressed in an in vitro transcription-translation system, E. coli, yeast, or plants, is unable to convert ferulic acid to vanillin. Rather, the protein is a component of an enzyme complex that preferentially converts 4-coumaric acid to 4-hydroxybenzaldehyde, as demonstrated by the purification of this complex and peptide sequencing. Furthermore, RNA sequencing provides evidence that this protein is expressed in many tissues of V. planifolia irrespective of whether or not they produce vanillin. On the basis of our results, V. planifolia does not appear to contain a cysteine protease-like "vanillin synthase" that can, by itself, directly convert ferulic acid to vanillin. The pathway to vanillin in V. planifolia is yet to be conclusively determined.

Arabidopsis phosphoinositide-specific phospholipase C 4 negatively regulates seedling salt tolerance.

Previous physiological and pharmacological studies have suggested that the activity of phosphoinositide-specific phospholipase C (PI-PLC) plays an important role in regulating plant salt stress responses by altering the intracellular Ca2+ concentration. However, the individual members of plant PLCs involved in this process need to be identified. Here, the function of AtPLC4 in the salt stress response of Arabidopsis seedlings was analysed. plc4 mutant seedlings showed hyposensitivity to salt stress compared with Col-0 wild-type seedlings, and the salt hyposensitive phenotype could be complemented by the expression of native promoter-controlled AtPLC4. Transgenic seedlings with AtPLC4 overexpression (AtPLC4 OE) exhibited a salt-hypersensitive phenotype, while transgenic seedlings with its inactive mutant expression (AtPLC4m OE) did not exhibit this phenotype. Using aequorin as a Ca2+ indicator in plc4 mutant and AtPLC4 OE seedlings, AtPLC4 was shown to positively regulate the salt-induced Ca2+ increase. The salt-hypersensitive phenotype of AtPLC4 OE seedlings was partially rescued by EGTA. An analysis of salt-responsive genes revealed that the transcription of RD29B, MYB15 and ZAT10 was inversely regulated in plc4 mutant and AtPLC4 OE seedlings. Our findings suggest that AtPLC4 negatively regulates the salt tolerance of Arabidopsis seedlings, and Ca2+ may be involved in regulating this process.

Analysis of crystal structure of Arabidopsis MPK6 and generation of its mutants with higher activity.

Mitogen-activated protein kinase (MAPK) cascades, which are the highly conserved signalling modules in eukaryotic organisms, have been shown to play important roles in regulating growth, development, and stress responses. The structures of various MAPKs from yeast and animal have been solved, and structure-based mutants were generated for their function analyses, however, the structures of plant MAPKs remain unsolved. Here, we report the crystal structure of Arabidopsis MPK6 at a 3.0 Å resolution. Although MPK6 is topologically similar to ERK2 and p38, the structures of the glycine-rich loop, MAPK insert, substrate binding sites, and L16 loop in MPK6 show notable differences from those of ERK2 and p38. Based on the structural comparison, we constructed MPK6 mutants and analyzed their kinase activity both in vitro and in planta. MPK6(F364L) and MPK6(F368L) mutants, in which Phe364 and Phe368 in the L16 loop were changed to Leu, respectively, acquired higher intrinsic kinase activity and retained the normal MAPKK activation property. The expression of MPK6 mutants with basal activity is sufficient to induce camalexin biosynthesis; however, to induce ethylene and leaf senescence, the expression of MPK6 mutants with higher activity is required. The results suggest that these mutants can be used to analyze the specific biological functions of MPK6.