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Circadian clocks are biological timekeeping systems that coordinate genetic, metabolic and physiological behaviors with the external day–night cycle. The clock in plants relies on the transcriptional-translational feedback loops transcription-translation feedback loop (TTFL), consisting of transcription factors including PSUEDO-RESPONSE REGULATOR (PRR) proteins, plant lineage–specific transcriptional repressors. Here, we report that a novel synthetic small-molecule modulator, 5-(3,4-dichlorophenyl)-1-phenyl-1,7-dihydro-4H-pyrazolo[3,4-d] pyrimidine-4,6(5H)-dione (TU-892), affects the PRR7 protein amount. A clock reporter line of Arabidopsis was screened against the 10,000 small molecules in the Maybridge Hitfinder 10K chemical library. This screening identified TU-892 as a period-lengthening molecule. Gene expression analyses showed that TU-892 treatment upregulates CIRCADIAN CLOCK–ASSOCIATED 1 (CCA1) mRNA expression. TU-892 treatment reduced the amount of PRR7 protein, a transcriptional repressor of CCA1. Other PRR proteins including TIMING OF CAB EXPRESSION 1 were altered less by TU-892 treatment. TU-892-dependent CCA1 upregulation was attenuated in mutants impaired in PRR7. Collectively, TU-892 is a novel type of clock modulator that reduces the levels of PRR7 protein. [ABSTRACT FROM AUTHOR]

In multi-step phosphorelay (MSP) signaling, upon reception of various environmental signals, histidine kinases (HKs) induce autophosphorylation and subsequent phosphotransfer to partner histidine-containing phosphotransfer proteins (HPts). Recently, we reported that (i) two Per-Arnt-Sim (PAS) domain-containing HKs (PHK1 and PHK2) of the moss Physcomitrium (Physcomitrella) patens suppressed red light-induced branching of protonema tissue, and (ii) they interacted with partner HPts (HPt1 and HPt2) in the nucleus in the dark while cytoplasmic interactions also occurred under red light. Here we demonstrate that PHK1 is diurnally regulated, i.e. , it is localized and interacts with HPt1 and HPt2 in the nucleus at night whereas these activities reversibly expand and become nucleocytoplasmic in the day. In the dark, PHK1 interacts with HPts only in the nucleus, even in subjective daytime, indicating that endogenous regulation by the circadian clock is not involved. These results suggest that PHK1 is a regulator of moss' adaptation to a light environment on a daily timescale. We discuss a possible regulatory mechanism for the branching of protonema. [Display omitted] • Localization of PHK1 is diurnally regulated, nuclear by night and nucleocytoplasmic by day. • Interactions of PHK1 with HPt1/2 are similarly regulated, nuclear by night and nucleocytoplasmic by day. • These properties of PHK1 provide a novel regulatory framework of plant MSPs. [ABSTRACT FROM AUTHOR]

In Escherichia coli, capsular colanic acid polysaccharide synthesis is regulated through the multistep RcsC[right arrow]YojN[right arrow]RcsB phosphorelay. By monitoring a hallmarked cps::lacZ reporter gene, we first searched for physiological stimuli that propagate the Rcs signaling system. The expression of cps::lacZ was activated when cells were grown at a low temperature (20[degrees]C) in the presence of glucose as a carbon source and in the presence of a relatively high concentration of external zinc (1 mm Zn[Cl.sub.2]). In this Rcs signaling system, the rcsF gene product (a putative outer membrane-located lipoprotein) was also an essential signaling component. Based on the defined signaling pathway and physiological stimuli for the Rcs signaling system, we conducted genomewide analyses with microarrays to clarify the Rcs transcriptome (i.e., Rcs regulon). Thirty-two genes were identified as putative Rcs regulon members; these genes included 15 new genes in addition to 17 of the previously described cps genes. Using a set of 37 two-component system mutants, we performed alternative genome-wide analyses. The results showed that the propagation of the zinc-responsive Rcs signaling system was largely dependent on another two-component system, PhoQ/P. Considering the fact that the PhoQ/P signaling system responds to external magnesium, we obtained evidence which supports the view that there is a signaling network that connects the Rcs system with the PhoQ/P system, which coordinately regulates extracellular polysaccharide synthesis in response to the external concentrations of divalent cations.

The yhhP gene of Escherichia coli encodes a 81-residue protein that contributes to the stability of the sigma-s, a stress-induced sigma factor. Analysis of deletion mutants reveals that this protein is essential to the general physiology of Escherichia. Organisms deficient in yhhP fail to thrive in standard laboratory rich media and assume filamentous morphology. This protein has homologs in a wide range of bacterial species.

Multi‐step phosphorelay (MSP) is a broadly distributed signaling system in organisms. In MSP, histidine kinases (HKs) receive various environmental signals and transmit them by autophosphorylation followed by phosphotransfer to partner histidine‐containing phosphotransfer proteins (HPts). Previously, we reported that Per‐Arnt‐Sim (PAS) domain‐containing HK1 (PHK1) and PHK2 of the moss Physcomitrium (Physcomitrella) patens repressed red light‐induced protonema branching, a critical step in the moss life cycle. In plants, PHK homolog‐encoding genes are conserved only in early‐diverging lineages such as bryophytes and lycophytes. PHKs‐mediated signaling machineries attract attention especially from an evolutionary viewpoint, but they remain uninvestigated. Here, we studied the P. patens PHKs focusing on their subcellular patterns of localization and interaction with HPts. Yeast two‐hybrid analysis, a localization assay with a green fluorescent protein, and a bimolecular fluorescence complementation analysis together showed that PHKs are localized and interact with partner HPts mostly in the nucleus, as unprecedented features for plant HKs. Additionally, red light triggered the interactions between PHKs and HPts in the cytoplasm, and light co‐repressed the expression of PHK1 and PHK2 as well as genes encoding their partner HPts. Our results emphasize the uniqueness of PHKs‐mediated signaling machineries, and functional implications of this uniqueness are discussed. [ABSTRACT FROM AUTHOR]