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Tree Genetics and Molecular Breeding 2012, Vol.2, No.2, 8
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Table 3 The molecular evolution relative rate of ITS sequences in different clusters of
Buxus genus
Group1/Group2
ITS
-
1
ITS
-
2
ITS
-
1
△
K
P
△
K
P
△
K
P
Ⅲ
/
Ⅰ
-
0.0763±0.0185
0.009**
-
0.0094±0.0024
0.011*
-
0.0191±0.0033
0.002**
Ⅲ
/
Ⅱ
0.0202±0.0061
0.030*
-
0.0004±0.0026
0.877
0.0092±0.0019
0.009**
Ⅳ
/
Ⅰ
-
0.1652±0.0343
0.005**
-
0.0051±0.0184
0.809
-
0.0517±0.0033
0.000**
Ⅳ
/
Ⅱ
-
0.0687±0.0350
0.121
0.0039±0.0184
0.851
-
0.0234±0.0018
0.000**
Ⅳ
/
Ⅲ
-
0.0889±0.0348
0.063
0.0044±0.0185
0.825
-
0.0326±0.0007
0.000**
Ⅳ
/
Ⅶ
-
0.1133±0.0337
0.006**
0.0005±0.0185
0.982
-
0.0375±0.0042
0.000**
Ⅴ
/
Ⅰ
-
0.0610±0.0423
0.200
0.1007±0.0238
0.024*
0.0256±0.0188
0.223
Ⅴ
/
Ⅱ
0.0355±0.0468
0.483
0.1097±0.0281
0.011*
0.0539±0.0220
0.058
Ⅴ
/
Ⅲ
0.0153±0.0467
0.756
0.1102±0.0281
0.011*
0.0447±0.0220
0.098
Ⅴ
/
Ⅳ
0.1042±0.0549
0.116
0.1058±0.0320
0.021*
0.0773±0.0220
0.017*
Ⅴ
/
Ⅶ
0.0170±0.0410
0.684
0.1061±0.0240
0.019*
0.0485±0.0140
0.003**
Note: The ITS sequence of
Pachysandra
terminalis
as reference ,
△
K is the margin of two groups substitution numbers relatively,
Positive means that evolution rate of group 1 is faster than that of group 2, Negative is reverse; * means P < 0.05, ** means P < 0.01
that pearl boxwood (Buxus sinica var.
parvifolia
) was
a kind of the
Buxus
sinica
’s variant. In this study we
found that pearl boxwood (
Buxus
sinica
var.
parvifolia
)
was not a variant of
Buxus
sinica
, but could be a kind
of sister species, the rate of molecular evolution
detected was different rates of evolution, the evolution
rate of
Buxus
sinica
was significantly higher than that
of the pearl boxwood (
Buxus
sinica
var.
parvifolia
).
The karyotype analysis in our laboratory also
confirmed that two species was not the same plant
species, the former (
Buxus
sinica
var.
parvifolia
).
Would be more advanced evolutionary than the latter.
In contrast,
B.
henryi
would be much closer in the
relationship than the pearl boxwood, which also had
some supporting results in karyotype analysis. Ther-
efore, the authors thought that pearl boxwood (
Buxus
sinica
var.
parvifolia
) was not a variant of
Buxus
sinica
,
but whether pearl boxwood could be considered as
being independent species, which it remains to be
validated by the barcoding genes such as
matK
and
rbcL
or other genes.
There are many plant species in
Buxus
genus, 17
species existing in China only, and mainly distributed
in the southwest of China. Therefore, Acquiring plant
materials would be the difficulty to build the
completely phylogenetic relationships of
Buxus
genus,
which we will step up the work in our lab. Authors
believed that, the difficulty in genus
Buxus
for
classifying different groups might be due to the
inter-species hybridization and continuity of the
morphological variation. If we directly study the
phylogenetic relationships of the genus at the DNA
levels, it would play a great action to overcome the
synonyms or homonym in genus as well as to promote
the studies for domestication and breeding of
Buxus
plant, biodiversity research and applications in garde-
ning and landscape.
Molecular systematics is to study the history of biolo-
gical evolution and reconstruction of phylogenetic
relationships based on the information of biological
macromolecules, of which the theoretical basis,
known as the “molecular clock hypothesis”, is the
evolutionary rate is relatively constant with biological
macromolecules in the evolutionary events (Tang et
al., 2002). However, since the hypothesis has been
proposed, there were more contentious in the studies
of phylogenetics in higher organisms (Muse, 2000),
especially, whether the rate of molecular evolution in
different cluster groups of the same organisms is
relatively consistent. Many scholars have long suspe-
cted that this hypothesis be reasonable, and some
experimental evidenceshas been come out negative,
for examples, Hartl and Clark (1997) and Vawter and
Brown (1986) independently proposed that different
gene should have different evolutionary rate. Zhang
and Ryder (1993) found the same gene should be
significantly differences in evolutionary rate in different
biological groups. Therefore, the same gene with
allometric phenomena of molecular evolution would
be one of the major challenges for molecular clock