No abstract

A Ca2+/calmodulin (CaM)-binding protein kinase from rice ( Oryza sativa ), OsCBK, has been characterized that lacks Ca2+-binding EF hands and has Ca2+/CaM-independent autophosphorylation and substrate-phosphorylation activity. OsCBK has all 11 subdomains of a kinase catalytic domain and a putative CaM-binding domain, and shares high identity with Ca2+-dependent-protein-kinase ('CDPK')-related protein kinases in plants. OsCBK bound CaM in a Ca2+-dependent manner as previously reported for Ca2+/calmodulin-dependent protein kinases in animals, but autophosphorylation and phosphorylation of histone IIIs were Ca2+/CaM-independent. Surface plasmon resonance analysis showed that OsCBK specifically bound CaM with high affinity ( K (D)=30 nM). Capillary electrophoresis showed that phosphorylation of OsCBK occurred on serine and threonine residues. These data show that OsCBK is a serine/threonine protein kinase that binds Ca2+/CaM, but whose enzymic activity is independent of Ca2+/CaM. In situ hybridization showed that OsCBK is expressed in reproductive and vegetative tissues of rice and shows temporal and spatial changes during plant growth and development. OsCBK is highly expressed in zones of cell division and it is particularly abundant in sporogenous cells of the anther at meiosis.

A s a form of nucleic acid-based silencing, RNA interference (RNAi) plays essential roles in the cellular response to viral infection in plants and invertebrates (3,13,34,50). In virus-infected cells, aberrant accumulation of viral single-stranded RNA (ssRNA) triggers its conversion into viral replicative intermediate double-stranded RNA (vRI-dsRNA), which is processed by the dsRNA-specific endonuclease Dicer into 21-to 23-nucleotide (nt) small interfering RNAs (siRNAs). Next, the virus-derived siRNAs (viRNAs) are transferred from Dicer to Argonaute (AGO) proteins in the RNA-induced silencing complex (RISC), which then guides the specific degradation of homologous viral ssRNAs (1,8,11,50). In mammals, RNAi directed by viral and cellular microRNAs (miRNAs) also contributes to host innate immunity against viral infection (18,27,35).To combat RNAi-mediated immunity, many plant and animal viruses encode viral suppressors of RNA silencing (VSRs) that target different components in the RNAi machinery. By sequestering dsRNA and siRNA, plant VSRs like turnip crinkle virus (TCV) capsid protein and tombusvirus P19 protein inhibit the production of siRNAs and hinder the incorporation of siRNAs into RISC (25, 41, 52). Additionally, direct interaction with AGO protein is known as a common approach of many plant and insect VSRs, such as cucumber mosaic virus (CMV) 2b protein, TCV P38 protein, sweet potato mild mottle virus (SPMMV) P1 protein, and cricket paralysis virus (CrPV) 1A protein, for suppressing RISC-mediated mRNA cleavage (2,17,36,54).Although Dicer plays essential roles in RNAi immunity, the mechanism by which Dicer can be directly targeted by VSRs is still poorly understood. The core protein of hepatitis C virus (HCV) was previously reported to interact with Dicer; however, whether this interaction is required for the RNA silencing suppression activity of HCV core protein has not been determined (7, 51). Furthermore, several VSRs have been reported to be able to target both RNA and protein components in the RNAi machinery. For example, TCV P38 was shown to target both RNA duplexes and AGO1 (2, 33). A question that remains to be answered, however, is whether an interrelationship exists between diverse activities of VSRs that mediate RNA binding and interaction with RNAi protein components (51).The ideal model for studying viral pathogenesis and RNAi immunity is the persistent infection of Drosophila melanogaster cells with Flock House virus (FHV), the most extensively studied member of the Nodaviridae family, which encodes a well-defined VSR designated B2 (1,6,10,16,29). During the course of FHV infection, 5=-terminal vRI-dsRNA initiated by viral RNA-dependent RNA polymerase (RdRP) triggers RNAi immunity, which is suppressed by B2 protein because B2 associates with RdRP and binds to vRI-dsRNA, thereby leading to the inhibition of the production of siRNAs by Dicer-2 (Dcr-2) (1). Recently, an interaction of FHV B2 with the Piwi-Argonaut-Zwille (PAZ) domain of Dcr-2 was detected in vitro (45). Although whether this in...

We report three new FRBs discovered by the Five-hundred-meter Aperture Spherical radio Telescope (FAST), namely FRB 181017.J0036+11, FRB 181118, and FRB 181130, through the Commensal Radio Astronomy FAST Survey (CRAFTS). Together with FRB 181123, which was reported earlier, all four FAST-discovered FRBs share the same characteristics of low fluence (≤0.2 Jy ms) and high dispersion measure (DM, >1000 pc cm−3), consistent with the anticorrelation between DM and fluence of the entire FRB population. FRB 181118 and FRB 181130 exhibit band-limited features. FRB 181130 is prominently scattered (τ s ≃ 8 ms) at 1.25 GHz. FRB 181017.J0036+11 has full-bandwidth emission with a fluence of 0.042 Jy ms, which is one of the faintest FRB sources detected so far. CRAFTS has started to build a new sample of FRBs that fills the region for more distant and fainter FRBs in the fluence–DME diagram, previously out of reach of other surveys. The implied all-sky event rate of FRBs is 1.24 − 0.90 + 1.94 × 10 5 sky−1 day−1 at the 95% confidence interval above 0.0146 Jy ms. We also demonstrate here that the probability density function of CRAFTS FRB detections is sensitive to the assumed intrinsic FRB luminosity function and cosmological evolution, which may be further constrained with more discoveries.