In Neurospora crassa, FRQ, WC-1, and WC-2 proteins comprise the core circadian FRQ-based oscillator that is directly responsive to light and drives daily rhythms in spore development and gene expression. However, physiological and biochemical studies have demonstrated the existence of additional oscillators in the cell that function in the absence of FRQ (collectively termed FRQ-less oscillators [FLOs]). Whether or not these represent temperature-compensated, entrainable circadian oscillators is not known. The authors previously identified an evening-peaking gene, W06H2 (now called clock-controlled gene 16 [ccg-16]), which is expressed with a robust daily rhythm in cells that lack FRQ protein, suggesting that ccg-16 is regulated by a FLO. In this study, the authors provide evidence that the FLO driving ccg-16 rhythmicity is a circadian oscillator. They find that ccg-16 rhythms are generated by a temperature-responsive, temperature-compensated circadian FLO that, similar to the FRQ-based oscillator, requires functional WC-1 and WC-2 proteins for activity. They also find that FRQ is not essential for rhythmic WC-1 protein levels, raising the possibility that this WCFLO is involved in the generation of WC-1 rhythms. The results are consistent with the presence of 2 circadian oscillators within Neurospora cells, which the authors speculate may interact with each other through the shared WC proteins.
Pyrocystis lunula (Schutt) Schutt has long been a model cell system in the study of circadian rhythms of bioluminescence and photosynthesis. Despite this, relatively little is known about the cell's ultrastructure. Here we report the complete serial reconstruction of P. lunula cells during both day and night phases (the first four dimensional study of any dinoflagellate). This permitted us to track both positional and ultrastructural changes in plastids and scintillons (the organelles responsible for bioluminescence). In daytime cells, plastids extended radially from the cell center with thylakoid membranes in stacks of two. Daytime scintillons clustered in a central region of the cell surrounded by the Cshaped nucleus. During the night, plastids were closely associated in the cell center with their thylakoids stacked in a grana-like arrangement. Nighttime scintillons were spread into the cell periphery. The daily migration of plastids and scintillons may depend on these organelles' interactions with the cells' cytoskeletal framework and appears to be under control of the circadian clock.
The ceramiaceous red algal genus Campylaephora J. Agardh includes three species that occur exclusively in the northwest Pacific Ocean. We studied the morphology, basiphyte range, and molecular phylogeny of Campylaephora borealis, considered a variety of the C. crassa complex, using material collected over its geographic range. Samples of C. borealis, C. crassa, C. hypnaeoides, and putative relatives were taken from 43 locations in Korea, Japan, and Far–East Russia, including the type localities of the first two of these species. Campylaephora borealis is distinguished by proliferous branchlets on all sides of the main branches and an alternate branching pattern. It is characteristically epiphytic on diverse plants, such as Prionitis divaricata, and occurs mostly in exposed sites. It is distributed from Maengbang, Korea to Nakhodka, Far–East Russia. Based on pairwise divergences of the plastid RuBisCo spacer region and psbA sequences, C. borealis is more closely related to C. hypnaeoides than to C. crassa. The topology of the tree constructed using the combined data shows the monophyly of C. borealis, which is clearly separated from other Campylaephora species and putative relatives. Our molecular data together with the basiphyte range and a morphological reappraisal point to the independent taxonomic position of C. borealis, isolated from Campylaephora crassa. Therefore, we propose to raise Campylaephora crassa f. borealis to the rank of species: Campylaephora borealis (Nakamura) Seo et al., stat. nov. The phylogeny of Campylaephora is also discussed.
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