A Duplicated NUCLEOLIN Gene with Antagonistic Activity Is Required for Chromatin Organization of Silent 45S rDNA in Arabidopsis

In plants as well as in animals, hundreds to thousands of 45S rRNA gene copies localize in Nucleolus Organizer Regions (NORs), and the activation or repression of specific sets of rDNA depends on epigenetic mechanisms. Previously, we reported that the Arabidopsis thaliana nucleolin protein NUC1, an abundant and evolutionarily conserved nucleolar protein in eukaryotic organisms, is required for maintaining DNA methylation levels and for controlling the expression of specific rDNA variants in Arabidopsis. Interestingly, in contrast with animal or yeast cells, plants contain a second nucleolin gene. Here, we report that Arabidopsis NUC1 and NUC2 nucleolin genes are both required for plant growth and survival and that NUC2 disruption represses flowering. However, these genes seem to be functionally antagonistic. In contrast with NUC1, disruption of NUC2 induces CG hypermethylation of rDNA and NOR association with the nucleolus. Moreover, NUC2 loss of function triggers major changes in rDNA spatial organization, expression, and transgenerational stability. Our analyses indicate that silencing of specific rRNA genes is mostly determined by the active or repressed state of the NORs and that nucleolin proteins play a key role in the developmental control of this process.     

'Lysobacter enzymogenes ssp. cookii ' Christensen 1978 should be recognized as an independent species, Lysobacter cookii sp. nov.

' Lysobacter enzymogenes ssp. cookii ' was proposed by Christensen and Cook in 1978; however, this subspecies name has not been cited in the Approved Lists of Bacterial Names and therefore the nomenclature has not been validated. In our genetic approach to clarify the relationships of the designated type strain of ' L. enzymogenes ssp. cookii ' PAGU 1119 (GenBank accession number ATCC29488 ) within the genus Lysobacter revealed that the strain was closely related to Lysobacter capsici YC5194 ^T (99.4%) rather than L. enzymogenes DSM2043 ^T (97.2%). The value for whole genome DNA–DNA relatedness between strain PAGU 1119 and L. enzymogenes DSM 2043^T or L. capsici YC5194 ^T was 20.7–26.1% or 60.9–62.0%, respectively. Although PAGU 1119 and L. capsici YC5194 ^T showed relatively high DNA relationships, the fatty acid profiles and some phenotypic characteristics were different, and we concluded that PAGU 1119 should be placed in a new species. We therefore propose a new species with the name Lysobacter cookii sp. nov. The type strain is PAGU 1119^T ( ATCC29488 ).     

Convenient Assay for Settlement Inducing Substances of Barnacles

A convenient assay method for estimation of barnacle, Balanus amphitrite, settlement inductive activity was developed. To avoid the inductive effect by comrades and laborious observation requirements, cyprid larvae were put individually into wells of a 96-well plate. The settlement ratio from the experiment without any inducers was quite low; therefore this assay allowed easy estimation of settlement inductive activities. Some known inductive agents, such as serotonin and barnacle extracts, clearly showed inductive activities. This assay method is proven to be suitable for estimation of barnacle settlement-inducing activities of both water-soluble and -insoluble compounds. Received October 31, 1997; accepted July 10, 1998.     

Seasonal dynamics of the fish parasite Neoplagioporus ayu (Digenea) in its definitive host, Plecoglossus altivelis, in the Chikugo River, Kyushu, Japan

Seasonal dynamics of the fish parasite Neoplagioporus ayu (Digenea; Opecoelidae; Plagioporinae) in its definitive host, the ayu Plecoglossus altivelis, in the Chikugo River, Kyushu, Japan, was examined. Natural ayu are amphidromous. In the upper Chikugo River, ayu fry raised in hatcheries are released into the river every spring because the migration of ayu is completely blocked by a dam that has no fish-pass channel. Ayu collected in April 2003 (within 1 month after release) harbored no N. ayu, but the prevalence of N. ayu rose to about 80% in May. The prevalence, abundance, and maturity of N. ayu were maintained at high levels from June to September. These finding indicate that the life cycle of N. ayu is completed in a freshwater area, although its intermediate hosts have not yet been identified despite the intense examination of invertebrates.