The COP1 ortholog PPS regulates the juvenile-adult and vegetative-reproductive phase changes in rice

Because plant reproductive development occurs only in adult plants, the juvenile-to-adult phase change is an indispensable part of the plant life cycle. We identified two allelic mutants, peter pan syndrome-1 (pps-1) and pps-2, that prolong the juvenile phase in rice (Oryza sativa) and showed that rice PPS is an ortholog of Arabidopsis thaliana CONSTITUTIVE PHOTOMORPHOGENIC1. The pps-1 mutant exhibits delayed expression of miR156 and miR172 and the suppression of GA biosynthetic genes, reducing the GA(3) content in this mutant. In spite of its prolonged juvenile phase, the pps-1 mutant flowers early, and this is associated with derepression of RAP1B expression in pps-1 plants independently of the Hd1-Hd3a/RFT1 photoperiodic pathway. PPS is strongly expressed in the fourth and fifth leaves, suggesting that it regulates the onset of the adult phase downstream of MORI1 and upstream of miR156 and miR172. Its ability to regulate the vegetative phase change and the time of flowering suggests that rice PPS acquired novel functions during the evolution of rice/monocots.     

Screening for resistance against Pseudomonas syringae in rice-FOX Arabidopsis lines identified a putative receptor-like cytoplasmic kinase gene that confers resistance to major bacterial and fungal pathogens in Arabidopsis and rice

Approximately 20,000 of the rice-FOX Arabidopsis transgenic lines, which overexpress 13,000 rice full-length cDNAs at random in Arabidopsis, were screened for bacterial disease resistance by dip inoculation with Pseudomonas syringae pv. tomato DC3000 (Pst DC3000). The identities of the overexpressed genes were determined in 72 lines that showed consistent resistance after three independent screens. Pst DC3000 resistance was verified for 19 genes by characterizing other independent Arabidopsis lines for the same genes in the original rice-FOX hunting population or obtained by reintroducing the genes into ecotype Columbia by floral dip transformation. Thirteen lines of these 72 selections were also resistant to the fungal pathogen Colletotrichum higginsianum. Eight genes that conferred resistance to Pst DC3000 in Arabidopsis have been introduced into rice for overexpression, and transformants were evaluated for resistance to the rice bacterial pathogen, Xanthomonas oryzae pv. oryzae. One of the transgenic rice lines was highly resistant to Xanthomonas oryzae pv. oryzae. Interestingly, this line also showed remarkably high resistance to Magnaporthe grisea, the fungal pathogen causing rice blast, which is the most devastating rice disease in many countries. The causal rice gene, encoding a putative receptor-like cytoplasmic kinase, was therefore designated as BROAD-SPECTRUM RESISTANCE 1. Our results demonstrate the utility of the rice-FOX Arabidopsis lines as a tool for the identification of genes involved in plant defence and suggest the presence of a defence mechanism common between monocots and dicots.     

Characterization and Transcription of the Genes Involved in Butyrate Production in Butyrivibrio fibrisolvens TypeI and II Strains

The genes in Butyrivibrio fibrisolvens that encode the enzymes involved in butyrate production were sequenced. In a type I strain (ATCC 19171(T)), the genes coding for the enzymes that catalyze the conversion from acetyl-CoA to butyryl-CoA, thl (thiolase), crt (crotonase), hbd (beta-hydroxybutyryl-CoA dehydrogenase), bcd (butyryl-CoA dehydrogenase), etfB (electron transfer flavoprotein [ETF]-beta), and etfA (ETF-alpha), were found to be clustered and arranged in this order. A type II strain (ATCC 51255) had the same clustered genes with the same arrangement, except that crt was not present in the clustered genes. The deduced amino acid sequences of these enzymes did not greatly differ between the two strains, and even between B. fibrisolvens and clostridia. Amino acid identity appeared to be higher within the same type than between types I and II. The clustered genes were shown to be cotranscribed, and constitutively transcribed without being affected significantly by culture conditions.     

Morphology,stomach contents and growth of the endangered salmonid,Sakhalin taimen <Emphasis Type="Italic">Hucho perryi</Emphasis>, captured in the Sea of Okhotsk,northern Japan: evidence of an anadromous form

Synopsis We describe a total of 25 anadromous Sakhalin taimen Hucho perryi collected on the coast of Sarufutsu, northern Hokkaido, Japan in June 1997 and 1999. We examined morphology, stomach contents and growth of three anadromous taimen (one male and two females) in detail, which were preserved in good condition. The three taimen were aged and one female still had some eggs retained in her abdomen. The stomach contents of the three taimen consisted of sand lance Ammodytes personatus Girard and sculpin Triglops sp. On the basis of scale analyses, the growth rate of the three taimen was estimated by using the back-calculation method, and the highest rates were observed at young ages. Guanine pigmentation was present at the base of the caudal fin of each taimen and is considered as a potential morphological trait to differentiate anadromous from fluvial specimens. Another anadromous taimen, of which some individuals had reared for more than 3 years in seawater are also reported. For the conservation of this rare and endangered species, their migration route between rivers and sea should be protected     

Topolins and hydroxylated thidiazuron derivatives are substrates of cytokinin O-glucosyltransferase with position specificity related to receptor recognition

Glucosides of trans-zeatin occur widely in plant tissues, formed either by O-glucosylation of the hydroxylated side chain or N-glucosylation of the purine ring structure. O-Glucosylation is stereo-specific: the O-glucosyltransferase encoded by the Phaseolus lunatus ZOG1 gene has high affinity for trans-zeatin as the substrate, whereas the enzyme encoded by the maize (Zea mays) cisZOG1 gene prefers cis-zeatin. Here we show that hydroxylated derivatives of benzyladenine (topolins) are also substrates of ZOG1 and cisZOG1. The m-OH and o-OH derivatives are the preferred substrate of ZOG1 and cisZOG1, respectively. Among the hydroxylated derivatives of thidiazuron tested, the only enzyme/substrate combination resulting in conversion was cisZOG1/(o-OH) thidiazuron. The abilities of these cytokinins to serve as substrates to the glucosyltransferases were in a large part correlated with their biological activities in the P. lunatus callus bioassay, indicating that there may be similarities between cytokinin-binding sites on the enzymes and cytokinin receptors. Further support for this interpretation is provided by cytokinin recognition studies involving the Arabidopsis (Arabidopsis thaliana) CRE1/WOL/AHK4 and maize ZmHK1 receptors. The AHK4 receptor responded to trans-zeatin and m-topolin, while the ZmHK1 receptor responded also to cis-zeatin and o-topolin. Three-dimensional molecular models of the substrates were applied to explain the results.     

KNOX homeobox genes potentially have similar function in both diploid unicellular and multicellular meristems, but not in haploid meristems

Members of the class 1 knotted-like homeobox (KNOX) gene family are important regulators of shoot apical meristem development in angiosperms. To determine whether they function similarly in seedless plants, three KNOX genes (two class 1 genes and one class 2 gene) from the fern Ceratopteris richardii were characterized. Expression of both class 1 genes was detected in the shoot apical cell, leaf primordia, marginal part of the leaves, and vascular bundles by in situ hybridization, a pattern that closely resembles that of class 1 KNOX genes in angiosperms with compound leaves. The fern class 2 gene was expressed in all sporophyte tissues examined, which is characteristic of class 2 gene expression in angiosperms. All three CRKNOX genes were not detected in gametophyte tissues by RNA gel blot analysis. Arabidopsis plants overexpressing the fern class 1 genes resembled plants that overexpress seed plant class 1 KNOX genes in leaf morphology. Ectopic expression of the class 2 gene in Arabidopsis did not result in any unusual phenotypes. Taken together with phylogenetic analysis, our results suggest that (a) the class 1 and 2 KNOX genes diverged prior to the divergence of fern and seed plant lineages, (b) the class 1 KNOX genes function similarly in seed plant and fern sporophyte meristem development despite their differences in structure, (c) KNOX gene expression is not required for the development of the fern gametophyte, and (d) the sporophyte and gametophyte meristems of ferns are not regulated by the same developmental mechanisms at the molecular level.     

Photoaffinity labeling identifies the substrate-binding site of mammalian squalene epoxidase

Squalene epoxidase (SE) catalyzes the conversion of squalene to (3S)-2,3-oxidosqualene. Photolabeling and site-directed mutagenesis were performed on recombinant rat SE (rrSE) in order to identify the location of the substrate-binding site and the roles of key residues in catalysis. Truncated 50-kDa rrSE was purified and photoaffinity labeled by competitive SE inhibitor (Ki=18.4 microM), [(3)H]TNSA-Dza. An 8-kDa CNBr/BNPS-skatole peptide was purified and the first 24 amino acids were sequenced by Edman degradation. The sequence PASFLPPSSVNKRGVLLLGDAYNL corresponded to residues 388-411 of the full-length rat SE. Three nucleophilic residues (Lys-399, Arg-400, and Asp-407) were labeled by [(3)H]TNSA-Dza. Triple mutants were prepared in which bulky groups were used to replace the labeled charged residues. Purified mutant enzymes showed lower enzymatic activity and reduced photoaffinity labeling by [(3)H]TNSA-Dza. This constitutes the first evidence as to the identity of the substrate-binding site of SE.