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Molecular Plant Breeding 2011, Vol.2, No.15, 101
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officinarum
, constitute two small branches,
respectively, on account of their close relationship
(Figure 6).
Figure 6 Molecular evolutionary analysis of rbcL DNA
sequences among different higher plants
Note: The plant names and accessions in Genbank of DNA
sequences are showed in turn as follows:
Nicotiana tabacum
(Accession: NC001879),
Solanum lycopersicum
(Accession:
NC007898),
Spinacia oleracea
(Accession: NC002202),
Arabidopsis thaliana
(Accession: NC000932),
Citrus sinensis
(Accession: NC008334),
Calycanthus floridus var. glaucus
(Accession: NC004993),
Phalaenopsis aphrodite subsp.
formosana
(Accession: NC007499),
Oryza sativa subsp.
japonica
(Accession: NC001320),
Saccharum officinarum
(Accession: NC006084),
Zea mays
(Accession:NC001666),
Cycas taitungensis
(Accession: NC009618),
Cathaya
argyrophylla
(Accession: NC014589),
Pinus thunbergii
(Accession: NC001631).
The molecular level evolutionary relationship was
applied in biological systemic taxology widespreadly,
after the advance of "molecular evolutionary clock"
and "neutral theory" in 1960s. A few divergences are
present in the application of molecular evolution to
biological taxonomy, due to the dispute of "constant
speed of sequence evolution" and "darwinian positive
selection" in academic world. However, it is
acknowledged that the evolutionary units above
family can be differentiated exactly with the
phylogenetic analysis of DNA and AA sequence,
which was proved adequately in this study. The
Zea
mays
and
Saccharum officinarum
are separated from
Oryza sativa subsp. Japonica
correctly (Figure 6), in
virtue of their closer relationship, even though all the
three plants belong to
Gramineae
.
2 Discussion
In this study, we demonstrated that the rbcLs from
different higher plants don't possess signal peptide,
transmembrane topological structure and the traits of
hydrophobic protein. The principal secondary
structural elements are α-helix and random coil. The
compositions and the physical and chemical
characteristics are similar, and extremely high
homologies were exhibited among different higher
plants. The evolutionary relationship reflected by
DNA sequences corresponds with traditional botanical
taxonomy.
It is known that the sequences and structures of rbcLs
from different higher plants get high homologies, and
the similarities of that are above 80%, while the
similarities of rbcSs are much smaller and less than
50%. All the analyzed rbcL ORFs from higher plants
are about 1434bp, and translate into polypeptides that
consist of nearly 477 AA residues (Table 1). The
similarities of the rbcL AA residues from different
higher plants are more than 97%, and the inferior
homological region in the rbcL polypeptide mainly
locates at the C-terminal (Figure 5). The high
homology of rbcLs indicates the importance of
structural stability in maintaining high catalytic
efficiency. Also, it implies that the overwhelming
majority of rbcL AA residues play a crucial role in
keeping the structural stability, as the report that the
RuBisCo catalytic efficiency can be altered obviously
when some AA residues of rbcL were substituted
(Chen et al., 1988; 1993; Seokjoo and Robert., 1997;
Bainbridge et al., 1998; Pippa et al., 1998).
As a double functional enzyme, RuBisCo catalyzes
the oxygenation reaction of RuBP when it is
catalyzing the carboxylation reaction of that. Because
of the characteristics of RuBisCo, the plant will suffer
a great loss of about 20-50% of the organic carbon,
fixed by the carboxylation reaction, no merely energy
(Li et al., 2001). So in theoretically, the improvement
of crop RuBisCo is a breakthrough point in crop
variety improvement using modern biotechnology, and
has a tempting perspective (Mann, 1999; Parry et al.,
2007). Up to now, rapid progress has been making in
studies on RuBisCo structures, biological functions
and regulations, and enzymatic characters, but it is