Summary
While angiosperm clocks can be described as an intricate network of interlocked transcriptional feedback loops, clocks of green algae have been modelled as a loop of only two genes. To investigate the transition from a simple clock in algae to a complex one in angiosperms, we performed an inventory of circadian clock genes in bryophytes and charophytes. Additionally, we performed functional characterization of putative core clock genes in the liverwort Marchantia polymorpha and the hornwort Anthoceros agrestis.Phylogenetic construction was combined with studies of spatiotemporal expression patterns and analysis of M. polymorpha clock gene mutants.Homologues to core clock genes identified in Arabidopsis were found not only in bryophytes but also in charophytes, albeit in fewer copies. Circadian rhythms were detected for most identified genes in M. polymorpha and A. agrestis, and mutant analysis supports a role for putative clock genes in M. polymorpha.Our data are in line with a recent hypothesis that adaptation to terrestrial life occurred earlier than previously expected in the evolutionary history of charophyte algae. Both gene duplication and acquisition of new genes was important in the evolution of the plant circadian clock, but gene loss has also contributed to shaping the clock of bryophytes.
In this study, the complete genome sequence of a Newcastle disease virus (NDV) isolate collected from an outbreak in 1995 in chickens was fully characterized and compared with other NDV sequences. The genome was found to be 15,192 nucleotides long and to consist of six genes in the order 3'-NP-P-M-F-HN-L-5', similar to other avian paramyxoviruses type-I. However, a six-nucleotide insertion was observed in the 5' non-coding regions of the nucleoprotein (NP) gene, a feature that is unique to some NDV isolates. The isolate shows the amino acid sequence (112)RRQKRF(117) at the cleavage site of the F protein, which is identical to a known motif for virulent pathotypes of NDV. The phylogenetic analysis of the coding region of the F gene indicated that this isolate belongs to genotype VI, more specifically to genotype VId, along with isolates from the other European countries (Denmark, Switzerland and Austria). The same genotype caused outbreaks in the Middle East and Greece in the late 1960s, and in Hungary, in the early 1980s, suggesting a common source for these outbreaks.
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