Histone modification in chromatin is one of the key control points in gene regulation in eukaryotic cells. Protein complexes composed of histone acetyltransferase or deacetylase, WD40 repeat protein, and many other components have been implicated in this process. Here, we report the identification and functional characterization of HOS15, a WD40-repeat protein crucial for repression of genes associated with abiotic stress tolerance through histone deacetylation in Arabidopsis. HOS15 shares high sequence similarity with human transducin-beta like protein (TBL), a component of a repressor protein complex involved in histone deacetylation. Mutation of the HOS15 gene renders mutant plants hypersensitive to freezing temperatures. HOS15 is localized in the nucleus and specifically interacts with histone H4. The level of acetylated histone H4 is higher in the hos15 mutant than in WT plants. Moreover, the stress inducible RD29A promoter is hyperinduced and associated with a substantially higher level of acetylated histone H4 in the hos15 mutant under cold stress conditions. Our results suggest a critical role for gene activation/repression by histone acetylation/deacetylation in plant acclimation and tolerance to cold stress.cold responsive gene expression ͉ freezing tolerance ͉ histone H4 deacetylation ͉ WD 40 protein

Cold, hyperosmolarity, and abscisic acid (ABA) signaling induce RD29A expression, which is an indicator of the plant stress adaptation response. Two nonallelic Arabidopsis thaliana (ecotype C24) T-DNA insertional mutations, cpl1 and cpl3, were identified based on hyperinduction of RD29A expression that was monitored by using the luciferase (LUC) reporter gene (RD29A::LUC) imaging system. Genetic linkage analysis and complementation data established that the recessive cpl1 and cpl3 mutations are caused by T-DNA insertions in AtCPL1 (Arabidopsis C-terminal domain phosphatase-like) and AtCPL3, respectively. Gel assays using recombinant AtCPL1 and AtCPL3 detected innate phosphatase activity like other members of the phylogenetically conserved family that dephosphorylate the C-terminal domain of RNA polymerase II (RNAP II). cpl1 mutation causes RD29A::LUC hyperexpression and transcript accumulation in response to cold, ABA, and NaCl treatments, whereas the cpl3 mutation mediates hyperresponsiveness only to ABA. Northern analysis confirmed that LUC transcript accumulation also occurs in response to these stimuli. cpl1 plants accumulate biomass more rapidly and exhibit delayed flowering relative to wild type whereas cpl3 plants grow more slowly and flower earlier than wild-type plants. Hence AtCPL1 and AtCPL3 are negative regulators of stress responsive gene transcription and modulators of growth and development. These results suggest that C-terminal domain phosphatase regulation of RNAP II phosphorylation status is a focal control point of complex processes like plant stress responses and development. AtCPL family members apparently have both unique and overlapping transcriptional regulatory functions that differentiate the signal output that determines the plant response. P lants tolerate environmental stress because of numerous physiological adaptations, which have been attributed to the function of various determinant genes (1). In Arabidopsis thaliana, transcription of RD (Responsive to Dehydration) (2) and COR (Cold Responsive) (3) genes is activated by cold or hyperosmotic stress. The plant hormone abscisic acid (ABA) activates transcription of some RD and COR genes through an interaction involving the cis element ABRE (ABA-responsive element) and basic leucine zipper transcription factors such as ABFs͞AREBs (4, 5). However, expression of some RD or COR genes is activated by low temperature or desiccation, independent of ABA, by the interaction of CBF͞DREB DNA-binding proteins with another cis element, DRE (6, 7). Overexpression of CBF͞DREB in transgenic Arabidopsis plants induces ectopic expression of RD͞COR genes and confers desiccation and cold tolerance (7,8).Recent genetic dissection of cold-, hyperosmolarity-, and ABA-induced signaling that regulates gene expression and adaptation indicates that the cascade signature is modulated by numerous positive and negative regulators (9-14). Signaling control of plant gene expression is known now to include components that function at various stages in mRNA metaboli...

Serotonin (5HT) is a pivotal signaling molecule that modulates behavioral and endocrine responses to diverse chemical and physical stimuli. We report cell-specific regulation of 5HT biosynthesis by transient receptor potential V(TRPV) ion channels in C. elegans. Mutations in the TRPV genes osm-9 or ocr-2 dramatically downregulate the expression of the gene encoding the 5HT synthesis enzyme tryptophan hydroxylase(tph-1) in the serotonergic chemosensory neurons ADF, but neither the mutation nor the double mutation of both channel genes affects other types of serotonergic neurons. The TRPV genes are expressed in the ADF neurons but not in other serotonergic neurons, and act cell-autonomously to regulate a neuron-specific transcription program. Whereas in olfactory neurons OSM-9 and OCR-2 function is dependent on ODR-3 Gα, the activity of ODR-3 or two other Gα proteins expressed in the ADF neurons is not required for upregulating tph-1 expression, thus the TRPV ion channels in different neurons may be regulated by different mechanisms. A gain-of-function mutation in CaMKII UNC-43 partially suppresses the downregulation of tph-1 in the TRPV mutants, thus CaMKII may be an effector of the TRPV signaling. Mutations in the TRPV genes cause worms developmentally arrest at the Dauer stage. This developmental defect is due in part to reduced 5HT inputs into daf-2/insulin neuroendocrine signaling.

We report the identification and characterization of an Arabidopsis mutant, hos10-1 (for high expression of osmotically responsive genes), in which the expression of RD29A and other stress-responsive genes is activated to higher levels or more rapidly activated than in wild-type by low temperature, exogenous abscisic acid (ABA), or salt stress (NaCl). The hos10-1 plants are extremely sensitive to freezing temperatures, completely unable to acclimate to the cold, and are hypersensitive to NaCl. Induction of NCED3 (the gene that encodes the rate-limiting enzyme in ABA biosynthesis) by polyethylene glycol-mediated dehydration and ABA accumulation are reduced by this mutation. Detached shoots from the mutant plants display an increased transpiration rate compared with wild-type plants. The hos10-1 plants exhibit several developmental alterations, such as reduced size, early flowering, and reduced fertility. The HOS10 gene encodes a putative R2R3-type MYB transcription factor that is localized to the nucleus. Together, these results indicate that HOS10 is an important coordinating factor for responses to abiotic stress and for growth and development

A hyper-osmotically sensitive mutant of Arabidopsis thaliana, designated hos3-1 (high expression of osmotically responsive genes), was identified based on its hyper-luminescence of RD29A:LUC promoter fusion plants upon treatment with NaCl and ABA. These responses implicate the disrupted gene as a direct or indirect negative regulator of the RD29A stress-responsive pathway. By sequencing the flanking regions of the T-DNA borders, it was determined that the disrupted gene is at locus At4g36830, annotated as encoding a putative protein with high homology to CIG30 (ELO2/FEN1). CIG30 has been implicated in synthesis of very long chain fatty acids (VLCFA), which are essential precursors for sphingolipids and ceramides. Altered stress responses characteristic of ABA-hypersensitivity, including reduced root growth inhibition and reduced germination with ABA treatment and reduced water loss from leaves, were exhibited by allelic hos3-1 and hos3-2 mutants. The hos3-2 mutant is partially suppressed in its transcript abundance and is inherited as a recessive trait. Further, the HOS3 ORF under the control of the 35SCaMV promoter restored wild-type NaCl- and ABA-root growth sensitivity as well as RD29A:LUC luminescence in mutant plants. We also show here that the HOS3 wild-type gene functionally complements the sensitivity of elo2 and elo3 yeast mutants to monensin. Furthermore, both hos3-1 and hos3-2 alleles shared increased sensitivity to the herbicide Metolachlor, which inhibits acyl chain elongation in synthesis of VLCFA, and HOS3 functionally complemented both elo2 and elo3 and restored levels of VLCFA. Together, these data establish that HOS3 inhibits ABA-mediated stress responses and implicate the VLCFA pathway and products as control points for several aspects of abiotic stress signaling and responses. The results also provide support for a role of ceramide in the control of stomatal behavior.

Caenorhabditis elegans OCR-2 (OSM-9 and capsaicin receptor-related) is a TRPV (vanilloid subfamily of transient receptor potential channel) protein that regulates serotonin (5-HT) biosynthesis in chemosensory neurons and also mediates olfactory and osmotic sensation. Here, we identify the molecular basis for the polymodal function of OCR-2 in its native cellular environment. We show that OCR-2 function in 5-HT production and osmotic sensing is governed by its N-terminal region upstream of the ankyrin repeats domain, but the diacetyl sensitivity is mediated by independent mechanisms. The ocr-2(yz5) mutation results in a glycine-to-glutamate substitution (G36E) within the N-terminal region. The G36E substitution causes dramatic downregulation of 5-HT synthesis in the ADF neurons, eliminates osmosensation mediated by the ASH neurons, but does not affect the response to the odorant diacetyl mediated by the AWA neurons. Conversely, wild-type sequence of the N-terminal segment confers osmotic sensitivity and upregulation of 5-HT production to a normally insensitive C. elegans homolog, OCR-4, but this chimeric channel does not respond to diacetyl stimuli. Furthermore, expression of either the mouse or human TRPV2 gene under the ocr-2 promoter can substantially restore 5-HT biosynthesis in ocr-2-null mutants but cannot improve the deficits in osmotic or olfactory sensation, suggesting that TRPV2 can substitute for the role of OCR-2 only in serotonergic neurons. Thus, different sensory functions of OCR-2 arise from separable intrinsic determinants, and specific functional properties of TRPV channel proteins may be selectively conserved across phyla.

We hypothesize that adiponectin and leptin may be capable of mediating some of the effects that body weight has on prostate cancer and that a mouse model may be effective to examine this hypothesis. We found that tumors from the TRAMP prostate cancer model expressed adiponectin and leptin receptors. TRAMP-C2 prostate cancer cell proliferation was reduced by adiponectin. Leptin was able to block the ability of adiponectin to reduce cell proliferation through altered signaling of the ERK pathway. Overall, this work suggests that adiponectin, leptin, and their receptors may play an important role in prostate cancer.

The kinase-associated protein phosphatase (KAPP) is a regulator of the receptor-like kinase (RLK) signaling pathway. Loss-offunction mutations rag1-1 (root attenuated growth1-1) and rag1-2, in the locus encoding KAPP, cause NaCl hypersensitivity in Arabidopsis thaliana. The NaCl hypersensitive phenotype exhibited by rag1 seedlings includes reduced shoot and primary root growth, root tip swelling, and increased lateral root formation. The phenotype exhibited by rag1-1 seedlings is associated with a specific response to Na 1 toxicity. The sensitivity to Na 1 is Ca 21 independent and is not due to altered intracellular K 1 /Na 1 . Analysis of the genetic interaction between rag1-1 and salt overly sensitive1 (sos1-14) revealed that KAPP is not a component of the SOS signal transduction pathway, the only Na 1 homeostasis signaling pathway identified so far in plants. All together, these results implicate KAPP as a functional component of the RLK signaling pathway, which also mediates adaptation to Na 1 stress. RLK pathway components, known to be modulated by NaCl at the messenger RNA level, are constitutively downregulated in rag1-1 mutant plants. The effect of NaCl on their expression is not altered by the rag1-1 mutation.Animal receptor Tyr kinases and receptor Ser/Thr kinases are cell surface enzyme-linked receptors that are activated by peptide ligands and initiate a diverse range of signal transduction pathways, including those that control cell growth, differentiation and survival, defensive responses. and metabolism (Holland and Holland, 2002). Receptor-like kinases (RLKs; a.k.a. plant receptor kinase; Cock et al., 2002) are animal receptor kinase orthologs in plants, so classified because of conserved structures that include an extracellular receptor, a transmembrane domain, and an intracellular kinase domain . The mechanisms by which RLKs activate and regulate downstream components of the signaling pathway resemble those of receptor Tyr kinases and receptor Ser/Thr kinases (Cock et al., 2002;. RLK activation occurs upon binding of an extracellular ligand to the plasma membrane-localized heterodimeric receptor form (Morris and Walker, 2003;Tichtinsky et al., 2003;Torii, 2004). Subsequently, the RLK complex undergoes autotransphosphorylation to form an active complex (Trotochaud et al., 1999(Trotochaud et al., , 2000Clark, 2001;Rojo et al., 2002). RLKs are also transcriptionally regulated (Becraft, 2002). Plant RLKs activate diverse signal transduction pathways, including those that control hormone responses Matsubayashi et al., 2002;Montoya et al., 2002;Scheer and Ryan, 2002;Yin et al., 2002;Szekeres, 2003), flower development (Williams et al., 1997;Stone et al., 1998), innate immunity against bacterial pathogens (Gomez-Gomez et al., 2001), self incompatibility (Braun et al., 1997), and root nodule formation (Downie and Walker, 1999;Endre et al., 2002;Krusell et al., 2002;Nishimura et al., 2002;Spaink, 2002;Stracke et al., 2002).The kinase-associated protein phosphatase (KAPP; Stone et al., 1994) is a cytosol...