Search

The past four decades have seen a dramatic increase in cropping area of japonicainbred rice after the 1980s and nowadays occupies 90% of the total cropping area in Jiangsu, east China. To date, little attention has been paid to the effects of genetic improvements of japonicainbred rice on grain yield and grain quality under different nitrogen (N) levels. Fifteen japonicainbred rice released from 1983 to 2014 were investigated to evaluate changes in grain yield and grain quality of japonicainbred rice under 180 kg N/ha (N180), 270 kg N/ha (N270), and 360 kg N/ha (N360) during genetic progress. Genetic improvement increased (p< .01) rice grain yield and annual gain was 47.1, 60.2, and 75.6 kg/ha under N180, N270, and N360, respectively. During genetic progress, milling quality (milled rice percentage and head rice percentage), appearance quality (chalky rice percentage, chalky degree, and grain length‐to‐width ratio), and cooking and eating quality (gel consistency, overall palatability, breakdown, and setback) have been improved, while nutritional quality has been declined because of a reducing trend of protein content. Generally, the application of N fertilizer improved nutritional quality but deteriorated milling quality, appearance quality, and cooking and eating quality. Higher N application increased grain protein content, gel consistency, and breakdown, while decreased setback, which resulted in poor overall palatability. The results suggested great improvements in both grain yield and grain quality (especially milling, appearance, and cooking and eating qualities) of japonicainbred rice since the 1980s in east China. Modern rice cultivars respond more favorably to increased N application in terms of grain yield. N application improved nutritional quality but downgrades other quality traits. Our results proved a great success in breeding high‐yielding and good‐quality japonicainbred rice in east China since the 1980s. Future rice breeding for higher grain yield and better grain quality should rely both on improvements of breeding selection and cultivation practices, particularly concerning N management strategies.

Salinity and drought are major abiotic stresses limiting plant growth and crop productivity. To evaluate the comparative effects of salt and drought stress on castor bean (Ricinus communis L.) germination and early seedling growth, a germination experiment and a seedling experiment were conducted to determine the responses of castor bean (cvs Zibi 5 and Zibi 9) to polyethylene glycol (PEG-6000) and sodium chloride (NaCl) with a range of gradient water potential levels, including 0 (control), –0.13 MPa, –0.2 MPa and –0.6 MPa. Results showed that both stresses caused by NaCl and PEG-6000 decreased germination percentage (GP), germination index (GI), fresh weight (FW), leaf gas exchange parameters (Pn, Ci and Tr) and chlorophyll pigments (Chl a and Chl b). The PEG-treated plants suffered higher restrictions in seed germination and seedlings growth than the NaCl-treated plants. Moreover, the PEG treatments caused more significant reductions in GP, Chl a, FW and Tr, as compared with NaCl treatment. On average, the GP under PEG stress was decreased by 22.3% and 22.0% for Zibi 5 and Zibi 9, respectively, in comparison to NaCl stress. Our study showed that both salt and water stress caused similar reductions in germination percentage, biomass accumulation, leaf gas exchange and chlorophyll pigments, while severer detrimental effects were induced by water stress as compared with salt stress.

In the areas where the soils are polluted by cadmium (Cd), farmers cannot afford to use their lands for remediation due to high demand for soybean (Glycine maxL.) production. In order to provide information for safe soybean production and achieve the phytoremediation using the root at the meantime, four soybean cultivars (mentioned as Cd excluder and Cd includer) differing in seed Cd accumulation were grown in a mixed growing media treated with different Cd concentrations (0 and 0.35  mg kg−1) in a growth cabinet. The biomass and Cd concentration in roots, stems, leaves, pods, and seeds were measured at the beginning of seed development (R5) and maturity (R8) stages; accumulation coefficient and translocation coefficient of Cd in different organs were calculated. Cadmium concentration in seeds was positively correlated with the Cd concentration in stem, leaf, and pod. Cadmium concentration in the roots of the Cd excluder was significantly higher than that in the Cd includer at the R5 and R8 stages; however, the Cd concentration in the seeds of the Cd includer was higher than that in the Cd excluder. Compared with the Cd excluder, more Cd was transported from the root to the aboveground organs of Cd includer. This suggests that Cd excluder with high cadmium accumulation in the root and low accumulation in the seed could provide a possible way to develop Cd‐safe cultivars with high phytoremediation capacity when grown on Cd‐polluted lands.

Salinity limits germination and plant growth and development in 45 million ha worldwide. Techniques to overcome this problem are needed. This project investigated the effects of jasmonic acid (JA) (0, 5, and 10 mM JA) and humic acid (HA) (0, 3, and 6 g HA kg−1soil) on growth and physiological parameters of forage sorghum (Sorghum bicolorL. Moench) under different NaCl salinity levels (0, 100, and 200 mM NaCl, with an equivalent electrical conductivity (EC) of 0.12 dSm−1as control treatment, 3.22, and 5.78 dSm−1, respectively). NaCl salinity reduced emergence percentage, emergence rate, salt tolerance index and seedling vigor index, all seedling growth parameters, ascorbate peroxidase (APX) activity, chlorophyll a, band total chlorophyll content. Proline content and soluble protein content were increased with salinity. At the 200 mM salinity level, seeds treated with 10 mM JA had a positive effect on emergence percentage, emergence rate, shoot length, total fresh weight, salt tolerance index, seedling vigor index, chlorophyll aand total chlorophyll content. At 200 mM NaCl salinity level, seeds treated with 6 g HA kg−1soil had increased root length, total dry weight, salt tolerance index, seedling vigor index, shoot length, protein content, APX, chlorophyll b, and total chlorophyll in seedlings. The application of 5 mM JA combined with 6 g HA kg−1soil was most effective in minimizing salinity stress. Our study suggested that the appropriate combined application of HA and JA could efficiently protect early seedlings from salt stress damage and alleviate abiotic stress.

Salinity is a growing problem worldwide, and techniques are needed to mitigate this problem. This study was conducted to determine if biochar (BC) can alleviate the adverse impacts of salinity stress on sorghum (Sorghum bicolorL.) seedling growth. Sorghum variety Kambal was sown in salinized soils at levels of 1.2, 3.1, and 7.3 dS m−1. The saline soils were treated with four BC rates of 0, 2, 4, and 8% (w/w). The test was a factorial design arranged as a completely randomized design with three replications. Seedling emergence percentage; root and shoot length; root and shoot dry weight; relative water content (RWC); and the activity of catalase (CAT), peroxidase (POD), and superoxide dismutase (SOD) were affected by the interaction between salinity and BC. At the 7.3 dS m−1salinity level, 2% BC increased seedling emergence percentage by 25.0% (P= .012). At the 7.3 dS m−1salinity level, 4% BC level increased root and shoot length (P= .009) and RWC by 46.0, 28.0, and 19.8% respectively. At the 7.3 dS m−1salinity level, 8% biochar decreased CAT by 50.6%. At the high salinity level, 4% BC decreased POD and SOD by 24.9 and 23.4%, respectively. Biochar amendment proved to be more useful to alleviate the effects of salinity on the seedling growth stage. These findings suggest that using BC in suitable amounts could mitigate the adverse effects of salinity, but excess BC application may have negative influences on seedling growth.

Salinity is a major abiotic stress limiting crop growth and reducing grain yield. In recent years, little progress was made in salt‐tolerant cultivation techniques. Therefore, a controlled experiment was conducted to study the effects of nitrogen management (NM) on growth, antioxidant ability, and yield performance of salt‐tolerant rice (Oryza sativaL.) under salinity stress. Three salinity levels (0‰ as control; 0.75‰, 4.3 dS m−1; and 1.5‰, 7.7 dS m−1) and four levels of NM (tillering fertilizer/panicle initiation fertilizer = 7:3, 6:4, 5:5, and 4:6) were arranged in this study. Under salinity stress, plant height, tiller number, fresh weight, grain yield, panicle, spikelets per panicle, grain weight, and soluble sugar content in stem were significantly decreased. In contrast, antioxidant parameters of superoxide dismutase, peroxidase, and catalase were significantly increased. Grain filling percentage and sucrose content were slightly changed. Compared to the control, grain yield was reduced by 45.6%, 34.8%, 60.4%, and 46.7% at the ratio of 7:3, 6:4, 5:5, and 4:6 NM at 0.75‰ salinity level, and 73.5%, 59.7%, 74.8%, and 61.7% at 1.5‰ salinity level, respectively. The highest yield was generated by 6:4 NM at both the 0.75‰ and 1.5‰ salinity level, and the lowest by 4:6 and 5:5. However, NM could obviously alleviate the inhibition effects of salinity stress and improve antioxidant ability of rice. Among them, 6:4 NM performed the best alleviation effects, followed by 7:3 and 5:5 NM. This study suggests that the appropriate NM can effectively alleviate salinity stress and increase grain yield.

Salinity is one of the most important factors that reduce the growth and antioxidant defense of plants. A controlled pot experiment was conducted to investigate the ameliorative effects of jasmonic acid (JA) priming (0, 5, and 10 mM) and humic acid (HA) (0, 3, and 6 g HA kg−1soil) amendment on antioxidant enzymes and salt tolerance of forage sorghum seedling (Sorghum bicolorL.) grown under three salinity conditions (0, 100, and 200 mM NaCl). Salinity stress reduced emergence seedling index (ESI), promptness index (PI), emergence stress tolerance index (ESTI), dry weight stress tolerance index (DWSTI), and the activities of the peroxidase (POD) and catalase (CAT) enzymes. The activity of superoxide dismutase (SOD) and malondialdehyde (MDA) content increased with salinity. Application of JA positively affected all parameters except CAT and MDA. Humic acid significantly increased all measured parameters except ESTI, DWSTI, and SOD activity. At the 200 mM NaCl level, JA and HA increased CAT, POD, SOD, ESI, DWSTI, ESTI, PI, and MDA as compared with the control. The application of HA at 6 g kg−1soil decreased SOD and ESI relative to the control at high salinity. The application of 10 mM JA combined with HA at 6 g kg−1soil was most effective in alleviating salinity stress. Therefore, the combined application of JA and HA on forage sorghum may improve salt tolerance and increase antioxidant enzymes that alleviate damages caused by salinity stress. Core IdeasApplication of jasmonic acid and humic acid (HA) mitigated salinity stress.Jasmonic acid (JA) and HA increased the antioxidant enzymes.Applying a combination of JA and HA at high levels of salinity improved salt tolerance. Application of jasmonic acid and humic acid (HA) mitigated salinity stress. Jasmonic acid (JA) and HA increased the antioxidant enzymes. Applying a combination of JA and HA at high levels of salinity improved salt tolerance.

We examined the yield component response to N fertilization under saline conditions.Nitrogen fertilization at moderate salinity exerts a positive and effective influence.Using urea fertilizer at high salt concentration was negative or ineffective. Salinity is a growing problem worldwide, and techniques are needed to mitigate this problem. This experiment was conducted to determine if nitrogen (N) fertilizer could mitigate the adverse effects of salinity on wheat (Triticum aestivumL.) production and yield. Two wheat varieties (Elnilein and Xumai 30) were seed into soil treated with NaCl at rates of 1.4, 2.5, 4.2, and 7.6 dS m−1. The NaCl‐treated soils were fertilized with three urea‐N rates (0, 86, and 210 kg N ha−1). Spike length, number of spikelets, number of kernels per spike, kernel weight per spike, and 1000 kernel weight were affected by interactions between variety and N and by interactions between salinity and N. At the 7.6 dS m−1salinity level, 210 kg N ha−1increased yield by 54.7%. This study showed that N alleviated the adverse effects of NaCl. Moreover, among all N levels used in this study, 86 and 210 kg N ha−1had similar impacts on wheat production. Across the N and salinity treatments, Xumai 30 generally had higher yields than Elnilein under different salinity and N levels. These findings suggest that cultural practices can reduce the impact of increasing salinity problems worldwide.

ABSTRACTRemote sensing has special advantages to monitor drug production that causes serious problems to global society. The widely used high spatial resolution images are too costly to make the full coverage of the opium poppy fields in a large area. Although the hyperspectral imagery acquired by Earth Observing-1 (EO-1) Hyperion that is free with medium spatial resolution has been employed, the used unsupervised multiple endmember spectral mixture analysis (MESMA)-based method is time-consuming for a large area. The present study used an unsupervised mixture-tuned matched filtering (MTMF)-based method to detect poppy fields from a Hyperion image covering a study area in Helmand, Afghanistan, and it achieved the producer’s, user’s and overall accuracies of 61%, 73% and 76%, as well as the kappa coefficient of 0.48. This method worked over 10 times faster than the MESMA-based method with similar detection accuracies. This MTMF-based method provides a potential alternative for the United Nations and the Afghanistan government to monitor opium poppy cultivation in Afghanistan.

The seeds of six wheat (Triticum aestivumL.) varieties from China (Xumai 30, Yang 10‐13, and Yang 11‐10) and Sudan (Argine, Buahin, and Elnilein) were cultured in NaCl solution containing (0, 50, 100, 150, 200, and 250 mM NaCl). Germination and early growth were determined. There were significant differences among salinity levels for water uptake, germination percentage, shoot and root length, dry weight, and salt tolerance index. At all salinity levels, the six varieties showed similar salt resistance, but each variety had different degrees of salt resistance. Argine had the highest germination percentage and germination index, and Yang 11‐10 had the highest reduction of total dry weight. Elnilein had a better salt tolerance index than the other varieties. Elnilein is recommended for saline soils. We suggest that a simple germination test would be a useful selection tool to use in developing new wheat lines for production on saline soils.

Low temperature and flooding are severe stresses to cotton plant growth and development in some parts of the world. This study was conducted to determine the interactive effects of low temperature and flooding on physiological and growth parameters of cotton plants, and yield of seed cotton. Transgenic Bt cotton plants at the boll-setting stage were treated with low temperature, flooding, and their combinations. The stresses decreased photosynthetic rate, stomatal conductance, transpiration rate, and intercellular CO2 concentration by up to 37%, 71%, 52%, and 60%, respectively. The content of soluble protein and insecticidal protein was also decreased by up to 65% and 53%, respectively. By contrast, malondialdehyde (MDA) content increased by up to 114%. The length of fruiting branch was shortened by combined low temperature and flooding stress. Boll number and weight were decreased by 3.2% and 28.1%, respectively. Seed cotton yield was decreased by up to 43.2%. Our results suggest that concurrent low temperature and flooding at the boll-setting stage negatively influenced leaf photosynthetic activities and insecticidal protein production, leading to poor protection and yield. We recommend that agronomic measures be designed to stabilise physiological activities and insecticidal protein production in Bt cotton plants under stress conditions.

Salinity and high temperature are major abiotic stresses limiting sustainable crop production. Seed priming is a useful tool to enhance seedling growth and the antioxidant defence system of crops under salinity and temperature stress. This experiment was designed to determine the effects of gibberellic acid (GA3, 288.7µm), kinetin (232.2µm) and salicylic acid (362µm) on some morphological and physiological parameters of sweet sorghum (Sorghum bicolor L. Moench) hybrid Yajin 13 under salinity (0, 100 and 200mm NaCl) and temperature (25°C and 37°C) stress. Salinity and high temperature significantly reduced emergence percentage, shoot and root lengths, number of leaves, shoot fresh and dry weight, and chlorophyll a and b content. The activity of superoxide dismutase (SOD) and malondialdehyde (MDA) content were increased with an increase in both salinity and temperature stress. Hormone treatments positively affected all parameters except root fresh and dry weight, number of leaves, SOD activity and chlorophyll a. Under salinity stress at 200mm NaCl, treatment with salicylic acid increased emergence percentage, emergence rate, chlorophyll b and protein content by 82.0%, 130%, 7.9% and 1.9%, respectively, relative to the control (no treatment). At 37°C, salicylic acid increased emergence percentage, emergence rate and number of roots by 72.5%, 108.5% and 63.8%, respectively, and decreased MDA content by 17.6% relative to the control. Our study indicated that seed priming with an appropriate concentration of exogenous hormones (salicylic acid, kinetin, GA3) is a useful, easy method for improving germination, seedling growth and the antioxidant defence system of sweet sorghum under conditions of high temperature and salinity.

Germination and vigorous growth are critical for seedling establishment, especially under salinity and high temperature. A laboratory experiment was done to determine the effects of salinity (0, 100, 200, and 300 mM NaCl) and temperature (25, 35, and 39°C) on germination and early seedling growth of two genotypes (Yajin 13 and Yajin 71) of sweet sorghum [Sorghum bicolor(L.) Moench]. Seeds were soaked in solutions with one of three hormones [288.7 μM gibberellic acid (GA3), 232.3μM kinetin, or their combination] and germinated under controlled conditions. Water imbibition, germination, radicle and shoot length, and the electrical conductivity of leachate were measured. Seed water imbibition increased with increasing temperature and decreased with increasing salinity level. Yajin 13 had 17.9% higher germination percentage with 16.3% higher germination velocity index than Yajin 71. Salinity and temperature stresses clearly affected germination and decreased subsequent shoot and root growth. The application of GA3, kinetin, or their combination alleviated the negative effects of salinity and temperature stresses on all the measurements. Among the tested hormones, GA3was better in alleviating salinity and temperature stress in both genotypes in germination and other parameters except water uptake. It was concluded that seeds treated with suitable exogenous hormones may serve as a possible way to improve water imbibition and to alleviate the negative effects produced by salinity and high temperature on germination and early seedling growth of sweet sorghum.

Salinity is a severe environmental factor that has limited the growth and productivity of crops. External application of regulating substances is a useful strategy to minimize the inhibitory effects of salinity on seedling growth. A controlled study was conducted to assess the interactive effects of exogenous gibberellic acid (GA3) addition and salinity on plant growth and antioxidant enzymes of castor bean (Ricinus communisL.) plants. The 50 mM level did not negatively affect the early growth of castor seedlings. At the 100 mM salinity level, however, seedling growth and physiological parameters were severely affected. Plant height, leaf area, and the weight of root, stem, leaf, and the whole plant was reduced by up to 21.7, 27.9, 33.3, 37.5, 33.2, and 34.5%, respectively. The activity of superoxide dismutase (SOD), peroxidases (POD), catalases (CAT), and proline content were also decreased by up to 32.0, 34.3, 53.6, and 212.4% at such a high salinity level. Presoaking seeds with 250 uM GA3increased plant height, stem diameter, and the weight of leaf and the whole plant by up to 13.3, 7.4, 66.7, and 39.1%, respectively. The activity of SOD and POD and the content of proline and soluble protein were also significantly increased when GA3was applied at 250 uM. This study indicated that exogenous addition of GA3at appropriate concentrations can be a useful strategy to promote early seedling growth of castor bean plants grown under saline conditions.

Castor bean (Ricinus communisL.) is grown on marginal lands that can be prone to having medium to high salt concentrations. This study was done to identify a salinity threshold level for castor bean emergence and stand establishment. Seedlings were first cultured in organic matter–soil mixed media at different salinity levels (0.5, 3.6, 7.1, 10.4, and 13.6 dS m−1) and then transplanted into pots filled with soils at similar salinity levels (0.4, 3.6, 7.1, 10.4, and 13.6 dS m−1). Emergence, survival, seedling growth, nutrient accumulation, and leaf photosynthetic parameters were determined. The salinity threshold level was identified at 7.1 dS m−1At this salinity level or lower, the emergence rate and survival rate reached 75% or higher; and seedling growth, nutrient accumulation, and leaf photosynthetic parameters were not severely affected. As the salinity level increased to 10.4 and 13.6 dS m−1, emergence rate dropped to below 70%, and survival rate below 50%. Photosynthetic rate and stomatal conductance were reduced by up to 66% and chlorophyll reading by up to 24%. Nutrient uptake and accumulation were also significantly reduced at these two salinity levels. Our results indicate that castor bean could be cultured in plastic seedling trays filled with organic matter–soil mixed seedling media and then transplanted into conventional soils provided that the salinity levels in seedling media and conventional soils are ≤7.1 dS m−1

Emergence and early seedling growth are critical for establishing reasonable plant population densities under saline stress conditions. An experiment with seashore mallow (Kosteletzkya virginicaL.) seedling culture in plastic nutrient‐rich matrices and transplanted into pots filled with soil from a local farm field was conducted under five salinity levels (0, 0.3, 0.6, 0.9, and 1.2%). Emergence, survival, growth, and physiological characteristics were monitored for 45 d after seeding. Increasing salinity levels from 0.3 to 1.2% inhibited seedling growth through the reduction in leaf size, leaf number, and physiological traits. At 45 d after seeding, there was a reduction of 13 to 47% in photosynthesis, 18 to 62% in soluble protein, 6 to 84% in superoxide dismutase activity, and 20 to 81% in root activities, whereas free amino acids increased by 34 to 104%, proline by 18 to 167%, and malondialdehyde by 20 to 220%. The reduction in photosynthesis was mainly associated with the reduction in stomatal conductance. Emergence and survival rates could be maintained at ≥60% at salinity levels ≤0.9%. Our results indicate that seashore mallow could grow in saline soils with seedling culture in nutrient‐rich plastic matrices and transplanted into conventional soils provided that the salinity levels in nutrient‐rich medium and conventional soils are ≤0.9%.

The involvement of dual specificity phosphatases (DSPs) in the mitogen-activated protein kinase (MAPK) signaling has been mostly limited to the inactivation of MAPKs by the direct dephosphorylation of the TXY motif within their activation loop. We report the cloning and characterization of a murine DSP, called JNK pathway-associated phosphatase (JKAP), which lacks the regulatory region present in most other MAP kinase phosphatases (MKPs) and is preferentially expressed in murine Lin−Sca-1+stem cells. Overexpression of JKAP in human embryonic kidney 293T cells specifically activated c-Jun N-terminal kinase (JNK) but not p38 and extracellular signal-regulated kinase 2. Overexpression of a mutant JKAP, JKAP-C88S, blocked tumor necrosis factor-α-induced JNK activation. Targeted gene disruption in murine embryonic stem cells abolished JNK activation by tumor necrosis factor-α and transforming growth factor-β, but not by ultraviolet-C irradiation, indicating that JKAP is necessary for optimal JNK activation. JKAP associated with JNK and MKK7, but not SEK1, in vivo. However, JKAP did not interact with JNK in vitro, suggesting that JKAP exerts its effect on JNK in an indirect manner. Taken together, these studies identify a positive regulator for the JNK pathway and suggest a novel role for DSP in mitogen-activated protein kinase regulation.

Protein phosphatase 4 (PP4, previously named protein phosphatase X (PPX)), a PP2A-related serine/threonine phosphatase, has been shown to be involved in essential cellular processes, such as microtubule growth and nuclear factor κB activation. We provide evidence that PP4 is involved in tumor necrosis factor (TNF)-α signaling in human embryonic kidney 293T (HEK293T) cells. Treatment of HEK293T cells with TNF-α resulted in time-dependent activation of endogenous PP4, peaking at 10 min, as well as increased serine and threonine phosphorylation of PP4. We also found that PP4 is involved in relaying the TNF-α signal to c-Jun N-terminal kinase (JNK) as indicated by the ability of PP4-RL, a dominant-negative PP4 mutant, to block TNF-α-induced JNK activation. Moreover, the response of JNK to TNF-α was inhibited in HEK293 cells stably expressing PP4-RL in comparison to parental HEK293 cells. The involvement of PP4 in JNK signaling was further demonstrated by the specific activation of JNK, but not p38 and ERK2, by PP4 in transient transfection assays. However, no direct PP4-JNK interaction was detected, suggesting that PP4 exerts its positive regulatory effect on JNK in an indirect manner. Taken together, these data indicate that PP4 is a signaling component of the JNK cascade and involved in relaying the TNF-α signal to the JNK pathway.

The c-Jun N-terminal kinase (JNK) signaling pathway is involved in transforming growth factor β (TGF-β) signaling in a variety of cell systems. We report here that hematopoietic progenitor kinase 1 (HPK1), a novel Ste20-like protein serine/threonine kinase, serves as an upstream mediator for the TGF-β-activated JNK1 cascade in 293T cells. TGF-β treatment resulted in a time-dependent activation of HPK1, which was accompanied by similar kinetics of JNK1 activation. The activation of JNK1 by TGF-β was abrogated by a kinase-defective HPK1 mutant but not by a kinase-defective mutant of kinase homologous to Ste20/Sps1. This result indicates that HPK1 is specifically required for TGF-β-induced activation of JNK1. We also found that TGF-β-induced JNK1 activation was blocked by a kinase-defective mutant of TGF-β-activated kinase 1 (TAK1). In addition, interaction between HPK1 and TAK1 was observed in transient transfection assays, and this interaction was enhanced by TGF-β treatment. Both stress-activated protein kinase/extracellular signal-regulated kinase kinase (SEK) and mitogen-activated protein kinase kinase 7 (MKK7) are immediate upstream activators of JNK1. Although SEK and MKK7 acted downstream of TAK1, only a kinase-defective SEK mutant blocked TGF-β-induced activation of JNK1, indicating that the TGF-β signal is relayed solely through SEK, but not MKK7,in vivo. Furthermore, TGF-β-induced activating protein 1 activation was blocked by a HPK1 mutant, as well as by TAK1 and SEK mutants. Taken together, these studies establish a potential cascade of TGF-β-activated interacting kinases beginning with HPK1, a Ste20 homolog, and ending in JNK1 activation: HPK1 → TAK1 → SEK → JNK1.

The yeast serine/threonine kinase STE20 activates a signaling cascade that includes STE11 (mitogen-activated protein kinase kinase kinase), STE7 (mitogen-activated protein kinase kinase), and FUS3/KSS1 (mitogen-activated protein kinase) in response to signals from both Cdc42 and the heterotrimeric G proteins associated with transmembrane pheromone receptors. Using degenerate polymerase chain reaction, we have isolated a human cDNA encoding a protein kinase homologous to STE20. This protein kinase, designated HPK/GCK-like kinase (HGK), has nucleotide sequences that encode an open reading frame of 1165 amino acids with 11 kinase subdomains. HGK was a serine/threonine protein kinase that specifically activated the c-Jun N-terminal kinase (JNK) signaling pathway when transfected into 293T cells, but it did not stimulate either the extracellular signal-regulated kinase or p38 kinase pathway. HGK also increased AP-1-mediated transcriptional activity in vivo. HGK-induced JNK activation was inhibited by the dominant-negative MKK4 and MKK7 mutants. The dominant-negative mutant of TAK1, but not MEKK1 or MAPK upstream kinase (MUK), strongly inhibited HGK-induced JNK activation. TNF-α activated HGK in 293T cells, as well as the dominant-negative HGK mutants, inhibited TNF-α-induced JNK activation. These results indicate that HGK, a novel activator of the JNK pathway, may function through TAK1, and that the HGK → TAK1 → MKK4, MKK7 → JNK kinase cascade may mediate the TNF-α signaling pathway.

Mitogen-activated protein kinase (MAPK) kinases (MKKs) are dual-specificity protein kinases that phosphorylate and activate MAPK. We have isolated a cDNA encoding a novel protein kinase that has significant homology to MKKs. The novel kinase MKK7 has a nucleotide sequence that encodes an open reading frame of 347 amino acids with 11 kinase subdomains. MKK7 is ubiquitously expressed in all adult and embryonic organs but displays high expression in epithelial tissues at later stages of fetal development. When transiently expressed in 293 cells, MKK7 specifically activated stress-activated protein kinases (SAPKs)/c-Jun N-terminal protein kinases (JNKs) but not extracellular-regulated kinase or p38 kinase. A kinase-negative mutant of MKK7 inhibits interleukin-1β, lipopolysaccharide, and MEKK1-induced SAPK/JNK activation. Thus, MKK7 is a new member of the MAPK kinase family that functions upstream of SAPK/JNK in the SAPK/JNK signaling pathway.

Transforming growth factor β (TGF-β)-activated kinase (TAK1) is known for its involvement in TGF-β signaling and its ability to activate the p38-mitogen-activated protein kinase (MAPK) pathway. This report shows that TAK1 is also a strong activator of c-Jun N-terminal kinase (JNK). Both the wild-type and a constitutively active mutant of TAK1 stimulated JNK in transient transfection assays. Mitogen-activated protein kinase kinase 4 (MKK4)/stress-activated protein kinase/extracellular signal-regulated kinase (SEK1), a dual-specificity kinase that phosphorylates and activates JNK, synergized with TAK1 in activating JNK. Conversely, a dominant-negative (MKK4/SEK1 mutant inhibited TAK1-induced JNK activation. A kinasedefective mutant of TAK1 effectively suppressed hematopoietic progenitor kinase-1 (HPK1)-induced JNK activity but had little effect on germinal center kinase activation of JNK. There are two additional MAPK kinase kinases, MEKK1 and mixed lineage kinase 3 (MLK3), that are also downstream of HPK1 and upstream of MKK4/SEK mutant. However, because the dominant-negative mutants of MEKK1 and MLK3 did not inhibit TAK1-induced JNK activity, we conclude that activation of JNK1 by TAK1 is independent of MEKK1 and MLK3. In addition to TAK1, TGF-β also stimulated JNK activity. Taken together, these results identify TAK1 as a regulator in the HPK1 → TAK1 → MKK4/SEK1 → JNK kinase cascade and indicate the involvement of JNK in the TGF-β signaling pathway. Our results also suggest the potential roles of TAK1 not only in the TGF-β pathway but also in the other HPK1/JNK1-mediated pathways.

We have previously shown that protein kinase C (PKC)-ζ is activated and required for nerve growth factor (NGF)-induced differentiation of rat pheochromocytoma PC12 cells (Wooten, M. W., Zhou, G., Seibenhener, M. L., and Coleman, E. S. (1994) Cell Growth & Diff.5, 395–403; Coleman, E. S., and Wooten, M. W. (1994) J. Mol. Neurosci.5, 39–57). Here we report the characterization and identification of a 106-kDa nuclear protein as a specific substrate of PKC-ζ. NGF treatment of PC12 cells resulted in translocation of PKC-ζ and coincident phosphorylation of a protein that was localized within the nucleoplasm of nuclei isolated from PC12 cells. Addition of PKC-ζ pseudosubstrate peptide in vitroor myristoylated peptidein vivodiminished phosphorylation of pp106 in a dose-dependent fashion. Likewise, addition of purified PKC-ζ, but neither PKC-α nor δ, to nuclear extracts resulted in an incremental increase in the phosphorylation of pp106. Expression of dominant-negative PKC-ζ inhibited NGF-induced phosphorylation of pp106, by comparison overexpression of PKC-ζ enhanced basal phosphorylation without a noticeable effect upon NGF-induced effects. Amino acid sequence analysis of four peptides derived from purified pp106 revealed that this protein was homologous to nucleolin. Using anin vitroreconstitution system, purified nucleolin was likewise shown to be phosphorylated by purified PKC-ζ. The staining intensity of both enzyme and substrate in the nucleus increased upon treatment with NGF. In vivolabeling with32Piand stimulation of PC12 cells with NGF followed by immunoprecipitation with anti-nucleolin antibody corroborated the in vitroapproach documenting enhanced phosphorylation of nucleolin by NGF treatment. Taken together, the findings presented herein document that nucleolin is a target of PKC-ζ that serves to relay NGF signals from cell surface to nucleus in PC12 cells.