PDF file: Annual Report 2002/2003 - Scottish Crop Research Institute

Director’s Report
diagnostics and therapeutics. It would appear from
studies on eukaryotic organisms that the components
of the mechanism are highly conserved between
species and organisational groups. In essence, genes
can be silenced by double-stranded RNA (dsRNA)
versions of their coding sequence, beginning with
pairs of the protein molecule Dicer binding to
dsRNA, cutting it into 22-nucleotide-long small interfering
RNA molecules (siRNA), which are then delivered
to the RNA-induced silencing protein complex
RISC which in turn contains nucleases, enzymes that
cleave RNA. Approaches to investigate and utilise the
RNAi machinery in knockout analyses and silencing
were best illustrated in the work on the nematode
Caenorhabditis elegans, a famous model system for
developmental biology. By use of specially constructed
plasmid clones, inducibly producing dsRNA for
16,757 of the organism’s 19,427 predicted open reading
frames, RNAi silencing effects were noted on genes
that are highly conserved in eukaryotes, and tend to be
clustered in regions of up to 1 million bases long.
Plants Plant scientists found much of relevance in the
research on animal stem cells, cells akin to plant
meristematic cells that can both replicate indefinitely
or give rise to a range of differentiated cells. Some
stem cells have a degree of pre-determination and are
committed to produce specific tissue types. Much of
the public and political debate over human stem cells
concentrated on the use of foetal cells and was tied
into issues of abortion and human cloning. Stem cells
derived from adult tissues that show varying degrees
of totipotency attracted a great deal of research, ethical,
and applied medical interest. In plants, the control
systems underpinning meristematic activity,
differentiation, de-differentiation, as well as cellular,
organismal, and population senescence, are now capable
of being unravelled by molecular genetics combined
with proteomics, metabolomics, and
bioinformatics.
Evolution A fascinating development in the understanding
of the origins and evolution of cellular
organelles in eukaryotes came with investigations on
the binary division of mitochondria and chloroplasts.
It is known that in prokaryotic cells, the functioning
of the contractile protein that causes the pinching and
binary fission of the cells (FtsZ), is dependent on the
hydrolysis of the nucleotide guanosine triphosphate
(GTP). FtsZ-dependent division also occurs in the
chloroplasts of green higher plants and algal mitochondria.
In contrast, yeast and nematode mitochondria
use another protein belonging to the dynamins
group of proteins which also draw on GTP hydrolysis.
It was proposed that an evolutionary transitionary
development of mitochondria took place in which
both FtsZ and the dynamin-related protein functioned
together, one on the inner surface of the inner
membrane surrounding the organelle, and one on the
outer surface of the inner membrane. Prospects for
discovering of such a transition phase were enhanced
by the fact that FtsZ has been found to form a constricting
ring on the inner surface of the inner membrane
of gram-negative bacteria, the chloroplasts of
green plants, and the mitochondria of red algae; the
dynamin-related protein has been found on the outer
surface of the inner membrane in higher-plant mitochondria.
The year 2002-2003 was one when a new conifer
species forming a new genus, Xanthocyparis, was discovered,
as well as a 125-million-year-old fossil of
Archaefructus sinensis, giving rise to the view that the
ancestors of the angiosperms may have been aquatic
weedy rather than highly lignified woody plants similar
to the magnolias. The commonly held concept of
low-biodiversity tropical rainforests in the Paleocene
was reconsidered after the discovery of a diverse fossil
leaf site was dated to a period only 1.4 million years
younger than the Cretaceous-Tertiary extinction event
65 million years ago. To put this into context, earth
is thought to have come into existence about 4,600
million years ago, but was thought to have been uninhabited
for the first half of this period – the Archean
Era or Eon. Life was generally believed to have
emerged in the succeeding Proterozoic Era. Often,
the Archaen and Proterozoic Eras are referred to as the
Precambian. There was structural evidence from
studies on single-celled eukaryotic algal fossils from
the Roper Group rocks in Australia, that the eukaryotic
life-form must have evolved between 2.5 billion and
2.7 billion years ago in the late Archean Eon. The
Precambian Era gave way to the Palaezoic (‘ancient
life; circa 550-248 million years ago; comprising (oldest
to youngest) the Cambrian, Ordovician, Silurian,
Devonian, Carboniferous, and Permian Periods), followed
by the Mesozoic Era (middle forms of life; circa
245-65 million years ago; comprising the Triassic,
Jurassic, and Cretaceous Periods), followed by the
Cenozoic Era (‘recent life’; from circa 65 million years
ago; comprising the Paleocene, Eocene, Oligocene,
Miocene, and Pliocene Epochs of the Tertiary Period,
and the more recent Pleistocene and Holocene Epochs
of the Quaternary Period). To accompany the evolutionary
considerations, I recommend the excellent
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