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The circadian clock allows plants to anticipate and adapt to periodic environmental changes. Organ- and tissue-specific properties of the circadian clock and shoot-to-root circadian signaling have been reported. While this long-distance signaling is thought to coordinate physiological functions across tissues, little is known about the feedback regulation of the root clock on the shoot clock in the hierarchical circadian network. Here, we show that the plant circadian clock conveys circadian information between shoots and roots through sucrose and K+. We also demonstrate that K+ transport from roots suppresses the variance of period length in shoots and then improves the accuracy of the shoot circadian clock. Sucrose measurements and qPCR showed that root sucrose accumulation was regulated by the circadian clock. Furthermore, root circadian clock genes, including PSEUDO-RESPONSE REGULATOR7 (PRR7), were regulated by sucrose, suggesting the involvement of sucrose from the shoot in the regulation of root clock gene expression. Therefore, we performed time-series measurements of xylem sap and micrografting experiments using prr7 mutants and showed that root PRR7 regulates K+ transport and suppresses variance of period length in the shoot. Our modeling analysis supports the idea that root-to-shoot signaling contributes to the precision of the shoot circadian clock. We performed micrografting experiments that illustrated how root PRR7 plays key roles in maintaining the accuracy of shoot circadian rhythms. We thus present a novel directional signaling pathway for circadian information from roots to shoots and propose that plants modulate physiological events in a timely manner through various timekeeping mechanisms.

To understand in detail the transcriptional and functional overlap of IFN-I and IFN-II activated responses, we used an integrative RNAseq-ChIPseq approach in Huh7.5 cells and characterized the genome-wide role of pSTAT1, pSTAT2, IRF9 and IRF1 in time-dependent ISG expression. For the first time, our results provide detailed insight in the timely steps of IFNα and IFNγ induced transcription, in which pSTAT1 and pSTAT2-containing ISGF3 and GAF-like complexes and IRF1 are recruited to individual or combined ISRE and GAS composite sites in a phosphorylation and time-dependent manner. Accordingly, composite genes displayed a more intermediate expression pattern, as compared to GAS (early) and ISRE genes (late), with the time- and phosphorylation-dependent recruitment of GAF, ISGF3 and IRF1 after IFNα stimulation and GAF and IRF1 after IFNγ. By sharing features of GAS and ISRE genes, composite genes were able to sustain IFN responsiveness in STAT1-, STAT2-, IRF9-, IRF1- and IRF9/IRF1-mutant Huh7.5 cells compared to Wt cells. Thus, the ISRE + GAS composite site acted as a molecular switch, depending on the timely available components and transcription factor complexes. As part of the increasing complexity, STAT1, STAT2 and IRF9 were identified as functional composite genes that are part of a positive feedback-loop controlling long-term IFNα and IFNγ responses. More important, in the absence of any one of the components, the positive feedback regulation of the ISGF3 and GAF components appeared to be preserved. Together, these findings provide further insight in the existence of a novel intracellular amplifier circuit prolonging ISG expression and controlling cellular responsiveness to different types of IFNs and subsequent antiviral activity. It also offers an explanation for the existing molecular and functional overlap between IFN-I and IFN-II activated ISG expression.

Cellular senescence is a stress-induced irreversible cell cycle arrest typically accompanied by expression of the cyclin-dependent kinase inhibitor p16INK4a (hereafter referred to as p16) and mitochondrial dysfunction1. Recent studies have indicated that p16-expressing senescent cells accumulate in the body over time and contribute to aging1, 2. Many stresses, such as telomere shortening and oncogene activation, induce senescence by damaging nuclear DNA1. However, the molecular mechanisms linking DNA damage to senescence remain unclear. Here, we show that the outer mitochondrial transmembrane protein BNIP3 drives senescence by triggering a DNA damage response (DDR) of mitochondria. BNIP3 was identified in a genome-wide siRNA screen for genes required for p16 expression upon DNA damage. Mass spectrometric analysis of BNIP3-interacting proteins yielded the DDR kinase ATM and subunits of the mitochondrial contact site and cristae organizing system (MICOS) complex. BNIP3 is an ATM substrate that increases the number of mitochondrial cristae upon DNA damage. This increase enhances the oxidation of fatty acids to acetyl-CoA, an acetyl group donor, thereby promoting histone acetylation and associated p16 expression. Our findings indicate that DDR signaling to mitochondria promotes p16 expression by altering mitochondrial structure and metabolism and highlight the importance of nuclear–mitochondrial communication in senescence induction.

Reactive oxygen species (ROS) play a central role in plant responses to biotic and abiotic stresses. ROS stimulate stomatal closure by inhibiting blue light (BL)-dependent stomatal opening under diverse stresses in the daytime. However, the stomatal opening inhibition mechanism by ROS remains unclear. In this study, we aimed to examine the impact of reactive carbonyl species (RCS), lipid peroxidation products generated by ROS, on BL signaling in guard cells. Application of RCS, such as acrolein and 4-hydroxy-(E)-2-nonenal (HNE), inhibited BL-dependent stomatal opening in the epidermis of Arabidopsis thaliana. Acrolein also inhibited H+ pumping and the plasma membrane H+-ATPase phosphorylation in response to BL. However, acrolein did not inhibit BL-dependent autophosphorylation of phototropins and the phosphorylation of BLUE LIGHT SIGNALING1 (BLUS1). Similarly, acrolein affected neither the kinase activity of BLUS1 nor the phosphatase activity of protein phosphatase 1, a positive regulator of BL signaling. However, acrolein inhibited fusicoccin-dependent phosphorylation of H+-ATPase and stomatal opening. Furthermore, carnosine, an RCS scavenger, partially alleviated the abscisic-acid- and hydrogen-peroxide-induced inhibition of BL-dependent stomatal opening. Altogether, these findings suggest that RCS inhibit BL signaling, especially H+-ATPase activation, and play a key role in the crosstalk between BL and ROS signaling pathways in guard cells.

Reactive oxygen species (ROS) function as key signaling molecules to inhibit stomatal opening and promote stomatal closure in response to diverse environmental stresses. However, how guard cells maintain basal intracellular ROS levels is not yet known. This study aimed to determine the role of autophagy in the maintenance of basal ROS levels in guard cells. We isolated the Arabidopsis autophagy-related 2 (atg2) mutant, which is impaired in stomatal opening in response to light and low CO(2) concentrations. Disruption of other autophagy genes, including ATG5, ATG7, ATG10, and ATG12, also caused similar stomatal defects. The atg mutants constitutively accumulated high levels of ROS in guard cells, and antioxidants such as ascorbate and glutathione rescued ROS accumulation and stomatal opening. Furthermore, the atg mutations increased the number and aggregation of peroxisomes in guard cells, and these peroxisomes exhibited reduced activity of the ROS scavenger catalase and elevated hydrogen peroxide (H(2)O(2)) as visualized using the peroxisome-targeted H(2)O(2) sensor HyPer. Moreover, such ROS accumulation decreased by the application of 2-hydroxy-3-butynoate, an inhibitor of peroxisomal H(2)O(2)-producing glycolate oxidase. Our results showed that autophagy controls guard cell ROS homeostasis by eliminating oxidized peroxisomes, thereby allowing stomatal opening.

Shape-persistent macrocycles and 3D nanocages have been prepared in one-pot under MeCN-promoted dynamic covalent bond conditions starting from silane catecholates, whose structures were confirmed by X-ray crystallography. Cation-exchange reactions of macrocycles and nanocages were performed along with the encapsulation of ammonium ions within the cavity of an anionic macrocycle and a tetrahedral nanocage.

Light-induced stomatal opening stimulates CO2 uptake and transpiration in plants. Weak blue light under strong red light effectively induces stomatal opening. Blue light-dependent stomatal opening initiates light perception by phototropins, and the signal is transmitted to a plasma membrane H+-ATPase in guard cells via BLUE LIGHT SIGNALING 1 (BLUS1) kinase. However, it is unclear how BLUS1 transmits the signal to H+-ATPase. Here, we characterized BLUS1 signaling in Arabidopsis thaliana, and showed that the BLUS1 C-terminus acts as an auto-inhibitory domain and that phototropin-mediated Ser-348 phosphorylation within the domain removes auto-inhibition. C-Terminal truncation and phospho-mimic Ser-348 mutation caused H+-ATPase activation in the dark, but did not elicit stomatal opening. Unexpectedly, the plants exhibited stomatal opening under strong red light and stomatal closure under weak blue light. A decrease in intercellular CO2 concentration via red light-driven photosynthesis together with H+-ATPase activation caused stomatal opening. Furthermore, phototropins caused H+-ATPase dephosphorylation in guard cells expressing constitutive signaling variants of BLUS1 in response to blue light, possibly for fine-tuning stomatal opening. Overall, our findings provide mechanistic insights into the blue light regulation of stomatal opening.

The production of cytokines in response to DNA damage events may be an important host defense response to help prevent the escape of pre-cancerous cells. The innate immune pathways involved in these events are known to be regulated by cellular molecules such as STING (stimulator of interferon genes), which controls type I interferon and pro-inflammatory cytokine production in response to the presence of microbial DNA or cytosolic DNA that has escaped from the nucleus. STING signaling has been shown to be defective in a variety of cancers, such as colon cancer and melanoma, actions which may enable damaged cells to escape the immunosurveillance system. Here, we report through examination of databases that STING signaling may be commonly suppressed in a greater variety of tumors due to loss-of-function mutation or epigenetic silencing of the STING/cGAS promoter regions. In comparison, RNA activated innate immune pathways controlled by RIG-I/MDA5 were significantly less affected. Examination of reported missense STING variants confirmed that many exhibited a loss of function phenotype and could not activate cytokine production following exposure to cytosolic DNA or DNA-damage events. Our data implies that the STING signaling pathway may be recurrently suppressed by a number of mechanisms in a considerable variety of malignant disease and be a requirement for cellular transformation.

Divalent Ni2+ cation-conducting solid electrolytes, (NixHf1−x)4/(4−2x)Nb(PO4)3, were successfully developed by introducing Ni2+ cations into a HfNb(PO4)3 solid exhibiting a three-dimensional NASICON-type structure. Although the HfNb(PO4)3 solid has been reported to be purely a Hf4+ ion conductor, the conducting species was changed to the divalent Ni2+ cation upon Ni2+ doping, due to the facile migration of lower-valence ions in the rigid crystal lattice. In addition, by selecting the well-ordered NASICON-type structure as the mother crystal, the (NixHf1−x)4/(4−2x)Nb(PO4)3 solid electrolytes exhibited lower activation energies and higher Ni2+ cation conductivities than a previously reported NiZr4(PO4)6 solid with the β-Fe2(SO4)3-type structure. Among the (NixHf1−x)4/(4−2x)Nb(PO4)3 solids, (Ni0.06Hf0.94)4/3.88Nb(PO4)3 (x = 0.06) showed the highest Ni2+ ion conductivity, of 2.27 × 10−4 S·cm−1 at 600 °C, which is ca. 23 times higher than that of the NiZr4(PO4)6 solid.

Tumor suppressor p53 plays an integral role in DNA-damage induced apoptosis, a biological process that protects against tumor progression. Cell shape dramatically changes when cells undergo apoptosis, which is associated with actomyosin contraction, however, it remains entirely elusive how p53 regulates actomyosin contraction in response to DNA-damaging agents. To identify a novel p53 regulating gene encoding the modulator of myosin, we conducted DNA microarray analysis. We found that, in response to DNA-damaging agent doxorubicin, expression of myotonic dystrophy protein kinase (DMPK), which is known to upregulate actomyosin contraction, was increased in a p53-dependent manner. The promoter region of DMPK gene contained potential p53-binding sequences and its promoter activity was increased by overexpression of the p53 family protein p73, but, unexpectedly, not of p53. Furthermore, we found that doxorubicin treatment induced p73 expression, which was significantly attenuated by downregulation of p53. These data suggest that p53 induces expression of DMPK through upregulating p73 expression. Overexpression of DMPK promotes contraction of the actomyosin cortex, which leads to formation of membrane blebs, loss of cell adhesion, and concomitant caspase activation. Taken together, our results suggest the existence of p53-p73-DMPK axis which mediates DNA-damage induced actomyosin contraction at the cortex and concomitant cell death.

Dectin-1 recognizes β-glucan and plays important roles for the antifungal immunity through the activation of spleen tyrosine kinase (Syk) in dendritic cells or macrophages. Recently, expression of Dectin-1 was also identified in human and mouse mast cells, although its physiological roles were largely unknown. In this report, rat mast cell line RBL-2H3 was analyzed to investigate the molecular mechanism of Dectin-1-mediated activation and responses of mast cells. Treatment of cells with Dectin-1-specific agonist curdlan induced tyrosine phosphorylation of cellular proteins and the interaction of Dectin-1 with the Src homology 2 domain of Syk. These responses depended on tyrosine phosphorylation of the hemi-immunoreceptor tyrosine-based activation motif in the cytoplasmic tail of Dectin-1, whereas they were independent of the γ-subunit of high-affinity IgE receptor. DNA microarray and real-time PCR analyses showed that Dectin-1-mediated signaling stimulated gene expression of transcription factor Nfkbiz and inflammatory cytokines, such as monocyte chemoattractant protein-1, IL-3, IL-4, IL-13, and tumor necrosis factor (TNF)-α. The response was abrogated by pretreatment with Syk inhibitor R406. These results suggest that Syk is critical for Dectin-1-mediated activation of mast cells, although the signaling differs from that triggered by FcϵRI activation. In addition, these gene expressions induced by curdlan stimulation were specifically observed in mast cells, suggesting that Dectin-1-mediated signaling of mast cells offers new insight into the antifungal immunity.

The opening of stomata in plants in response to blue light is driven by the plasma membrane H(+)-ATPase in guard cells. To evaluate the activation of the H(+)-ATPase in vivo, we can use H(+)-pumping by guard cells in response to blue light and fusicoccin. To do this, it is required to prepare a large amount of guard cell protoplasts and measure H(+)-pumping in the protoplasts. It is also necessary to determine the protein amount of H(+)-ATPase. In this protocol, we describe the procedures required for these preparations and measurements.

Macrophage-inducible C-type lectin (Mincle) interacts with the γ-subunit of high-affinity IgE receptor (FcεRIγ) and activates Syk by recognizing its specific ligand, trehalose-6,6′-dimycolate, a glycolipid produced by Mycobacterium tuberculosis. It has been suggested that mast cells participate in the immune defense against pathogenic microbes including M. tuberculosis, although the functions are still uncertain. In this study, we examined the Mincle-mediated signaling pathway and cellular responses using RBL-2H3 cells. Mincle formed a protein complex with not only FcεRIγ but also FcεRIβ in a stable cell line expressing myc-tagged Mincle. In addition, engagement of Mincle increased the levels of protein tyrosine phosphorylation and ERK phosphorylation. A pull-down assay demonstrated that cross-linking of Mincle induced binding of FcεRIβγ subunits to the Src homology 2 domain of Syk. Pharmacological and genetic studies indicated that activation of Syk was critical for Mincle-mediated activation of phospholipase Cγ2, leading to the activation of ERK and nuclear factor of activated T cells. Moreover, engagement of Mincle efficiently induced up-regulation of characteristic mast cell genes in addition to degranulation. Taken together, our present results suggest that mast cells contribute to Mincle-mediated immunity through Syk activation triggered by association with the FcεRIβγ complex.

Oncogenic Ras induces cell transformation and promotes an invasive phenotype. The tumor suppressor p53 has a suppressive role in Rasdriven invasion. However, its mechanism remains poorly understood. Here we show that p53 induces activation of the mitochondrial protease high-temperature requirement A2 (HtrA2; also known as Omi) and prevents Ras-driven invasion by modulating the actin cytoskeleton. Oncogenic Ras increases accumulation of p53 in the cytoplasm, which promotes the translocation of p38 mitogen-activated protein kinase (MAPK) into mitochondria and induces phosphorylation of HtrA2/Omi. Concurrently, oncogenic Ras also induces mitochondrial fragmentation, irrespective of p53 expression, causing the release of HtrA2/Omi from mitochondria into the cytosol. Phosphorylated HtrA2/Omi therefore cleaves β-actin and decreases the amount of filamentous actin (F-actin) in the cytosol. This ultimately down-regulates p130 Crk-associated substrate (p130Cas)-mediated lamellipodia formation, countering the invasive phenotype initiated by oncogenic Ras. Our novel findings provide insights into the mechanism by which p53 prevents the malignant progression of transformed cells. © 2014 Yamauchi et al., published_or_final_version

Tumor suppressor p53 prevents tumorigenesis and tumor growth by suppressing the activation of several transcription factors, including nuclear factor-κB (NF-κB) and STAT3. On the other hand, p53 stimulates actin cytoskeleton remodeling and integrin-related signaling cascades. Here, we examined the p53-mediated link between regulation of the actin cytoskeleton and activation of NF-κB and STAT3 in MCF-7 cells and mouse embryonic fibroblasts (MEFs). In the absence of p53, STAT3 was constitutively activated. This activation was attenuated by depleting the expression of p65, a component of NF-κB. Integrin β3 expression and lamellipodia formation were also downregulated by NF-κB depletion. Inhibition of integrin αvβ3, Rac1 or Arp2/3, which diminished lamellipodia formation, suppressed STAT3 activation induced by p53 depletion. These results suggest that loss of p53 leads to STAT3 activation via NF-κB-dependent lamellipodia formation. Our study proposes a novel role for p53 in modulating the actin cytoskeleton through suppression of NF-κB, which restricts STAT3 activation.

Interferon-α (IFN-α) and IFN-λ are structurally distinct cytokines that bind to different receptors, but induce expression of similar sets of genes through Janus kinase (JAK)-signal transducers and activators of transcription (STAT) pathways. The difference between IFN-α and IFN-λ signaling remains poorly understood. Here, using the CRISPR/Cas9 system, we examine the role of STAT1 and STAT2 in the inhibition of hepatitis C virus (HCV) replication by IFN-α and IFN-λ. Treatment with IFN-α increases expression of IFN-stimulated genes (ISGs) such as double-stranded RNA-activated protein kinase (PKR) and decreases viral RNA and protein levels in HCV-infected Huh-7.5 human hepatoma cells. These responses are only partially attenuated by knockout of STAT1 but are abolished by knockout of STAT2. In contrast, the inhibition of HCV replication by IFN-λ is abolished by knockout of STAT1 or STAT2. Microarray analysis reveals that IFN-α but not IFN-λ can induce expression of the majority of ISGs in STAT1 knockout cells. These findings suggest that IFN-α can inhibit HCV replication through a STAT2-dependent but STAT1-independent pathway, whereas IFN-λ induces ISG expression and inhibits HCV replication exclusively through a STAT1- and STAT2-dependent pathway.

Apoptosis signal-regulating kinase 1 (ASK1), a member of the mitogen-activated protein kinase kinase kinase family, plays pivotal roles in reactive oxygen species (ROS)-induced cellular responses. In resting cells, endogenous ASK1 constitutively forms a homo-oligomerized but still inactive high-molecular-mass complex including thioredoxin (Trx), which we designated the ASK1 signalosome. Upon ROS stimulation, the ASK1 signalosome unbinds from Trx and forms a fully activated higher-molecular-mass complex, in part by recruitment of tumor necrosis factor receptor-associated factor 2 (TRAF2) and TRAF6. However, the precise mechanisms by which Trx inhibits and TRAF2 and TRAF6 activate ASK1 have not been elucidated fully. Here we demonstrate that the N-terminal homophilic interaction of ASK1 through the N-terminal coiled-coil domain is required for ROS-dependent activation of ASK1. Trx inhibited this interaction of ASK1, which was, however, enhanced by expression of TRAF2 or TRAF6 or by treatment of cells with H2O2. Furthermore, the H2O2-induced interaction was reduced by double knockdown of TRAF2 and TRAF6. These findings demonstrate that Trx, TRAF2, and TRAF6 regulate ASK1 activity by modulating N-terminal homophilic interaction of ASK1.

Hepatitis C virus (HCV) nonstructural protein 5A (NS5A) is thought to regulate the replication of viral RNA and the assembly of virus particles in a serine/threonine phosphorylation-dependent manner. However, the host kinases that phosphorylate NS5A have not been fully identified. Here, we show that HCV particle assembly involves the phosphorylation of NS5A by the c-Abl tyrosine kinase. Pharmacological inhibition or knockdown of c-Abl reduces the production of infectious HCV (J6/JFH1) particles in Huh-7.5 cells without markedly affecting viral RNA translation and replication. NS5A is tyrosine-phosphorylated in HCV-infected cells, and this phosphorylation is also reduced by the knockdown of c-Abl. Mutational analysis reveals that NS5A tyrosine phosphorylation is dependent, at least in part, on Tyr(330) (Tyr(2306) in polyprotein numbering). Mutation of this residue to phenylalanine reduces the production of infectious HCV particles but does not affect the replication of the JFH1 subgenomic replicon. These findings suggest that c-Abl promotes HCV particle assembly by phosphorylating NS5A at Tyr(330).

Tumor suppressor p53 prevents tumorigenesis and tumor growth by suppressing the activation of several transcription factors, including nuclear factor-κB (NF-κB) and STAT3. On the other hand, p53 stimulates actin cytoskeleton remodeling and integrin-related signaling cascades. Here, we examined the p53-mediated link between regulation of the actin cytoskeleton and activation of NF-κB and STAT3 in MCF-7 cells and mouse embryonic fibroblasts (MEFs). In the absence of p53, STAT3 was constitutively activated. This activation was attenuated by depleting the expression of p65, a component of NF-κB. Integrin β3 expression and lamellipodia formation were also downregulated by NF-κB depletion. Inhibition of integrin αvβ3, Rac1 or Arp2/3, which diminished lamellipodia formation, suppressed STAT3 activation induced by p53 depletion. These results suggest that loss of p53 leads to STAT3 activation via NF-κB-dependent lamellipodia formation. Our study proposes a novel role for p53 in modulating the actin cytoskeleton through suppression of NF-κB, which restricts STAT3 activation.

Opening of stomata in the plant facilitates photosynthetic CO2 fixation and transpiration. Blue-light perception by phototropins (phot1, phot2) activates the plasma membrane H(+)-ATPase, causing stomata to open. Here we describe a regulator that connects these components, a Ser/Thr protein kinase, BLUS1 (BLUE LIGHT SIGNALING1), which mediates a primary step for phototropin signalling in guard cells. blus1 mutants identified by infrared thermography result in a loss of blue light-dependent stomatal opening. BLUS1 encodes a protein kinase that is directly phosphorylated by phot1 in vitro and in vivo at Ser-348 within its C-terminus. Both phosphorylation of Ser-348 and BLUS1 kinase activity are essential for activation of the H(+)-ATPase. blus1 mutants show lower stomatal conductance and CO2 assimilation than wild-type plants under decreased ambient CO2. Together, our analyses demonstrate that BLUS1 functions as a phototropin substrate and primary regulator of stomatal control to enhance photosynthetic CO2 assimilation under natural light conditions.

Fcγ receptor (FcγR)-mediated phagocytosis requires myosin II activity. Here we show that myosin II contributes to FcγR activation and subsequent F-actin assembly at the nascent phagocytic cup. Inhibition of myosin II attenuates phosphorylation of the immunoreceptor tyrosine-based activation motif (ITAM) of FcγR and binding of Syk to the ITAM. Furthermore, FcγR clusters independently of myosin II activity at the phagocytic cup, from which the receptor-like protein tyrosine phosphatase CD45 is excluded depending on myosin II activity. These findings suggest that myosin II-dependent segregation of CD45 from FcγR facilitates phosphorylation of the ITAM and triggers phagocytosis.

Protein phosphatase 1 (PP1) is a eukaryotic serine/threonine protein phosphatase comprised of a catalytic subunit (PP1c) and a regulatory subunit that modulates catalytic activity, subcellular localization and substrate specificity. PP1c positively regulates stomatal opening through blue light signaling between phototropins and the plasma membrane H(+)-ATPase in guard cells. However, the regulatory subunit functioning in this process is unknown. We identified Arabidopsis PRSL1 (PP1 regulatory subunit2-like protein1) as a regulatory subunit of PP1c. Tautomycin, a selective inhibitor of PP1c, inhibited blue light responses of stomata in the single mutants phot1 and phot2, supporting the idea that signals from phot1 and phot2 converge on PP1c. We obtained PRSL1 based on the sequence similarity to Vicia faba PRS2, a PP1c-binding protein isolated by a yeast two-hybrid screen. PRSL1 bound to Arabidopsis PP1c through its RVxF motif, a consensus PP1c-binding sequence. Arabidopsis prsl1 mutants were impaired in blue light-dependent stomatal opening, H(+) pumping and phosphorylation of the H(+)-ATPase, but showed normal phototropin activities. PRSL1 complemented the prsl1 phenotype, but not if the protein carried a mutation in the RVxF motif, suggesting that PRSL1 functions through binding PP1c via the RVxF motif. PRSL1 did not affect the catalytic activity of Arabidopsis PP1c but it stimulated the localization of PP1c in the cytoplasm. We conclude that PRSL1 functions as a regulatory subunit of PP1 and regulates blue light signaling in stomata.

Apoptosis signal-regulating kinase 1 (ASK1), a mitogen- activated protein kinase kinase kinase, plays pivotal roles in stress responses. In addition, ASK1 has emerged as a key regulator of immune responses elicited by pathogen-associated molecular patterns (PAMPs) and endogenous danger signals. Recent studies have demonstrated that reactive oxygen species (ROS)-dependent activation of ASK1 is required for LPS-stimulated cytokine production as well as extracellular ATP-induced apoptosis in immune cells. The mechanism of ROS-dependent regulation of ASK1 activity by thioredoxin and TRAFs has been well characterized. In this review, we focus on the molecular details of the activation of ASK1 and its involvement in innate immunity.