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Tree Genetics and Molecular Breeding 2012, Vol.2, No.2, 8
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11
and transversion of nucleotide in the region of ITS
-
2
leading to the results from one-parameter model being
less than that of the two-parameter model. So, using
the two-parameter model to analyze the molecular
evolution of the genus
Buxus
would be better
corresponding to the true situation. Thus, two-parameter
model was used to analyze the following results in this
research. As analysis of the coefficient of variation,
coefficient of variation of ITS
-
1 in Boxus was 12.4%,
of ITS
-
2 was 19.3%, which the later was significantly
larger than the former, indicating that variation of
ITS
-
1 sequence was less than that of ITS
-
2. Whereas,
coefficient of variation in 5.8S sequence was 63.8%,
which was significantly higher than that of the former
two sequences. The reason might be significant
changes occurring in the 5.8 S sequences of three
species of
B. glomerate
,
B. gonoclada
, and
B.
citrifolia,
whose numbers of conversions and
transversions were increased signifycantly, leading
to variation coefficient of 5.8S sequence increasing.
1.3 Relative rate of genus
Buxus
detected
First of all, using Phylip software to build phylogenetic
tree of the genus
Buxus
, and taking
Pachysandra
terminalis
as reference of the outgroup, the maximum
parsimony tree was constructed based on the Kimura
two-parameter model (Figure 1). In this study, the 18
tested plants of the genus
Buxus
can be divided into
three major branches,
B. macowanii
,
B. glomerata
,
B. gonoclada
and
B. citrifolia
assigned to a branch.
B.
sempervirens, B. bodinieri and B. balearica
assigned
to a group; the rest assigned to a branch. These three
groups were further divided into seven clustering
groups, serially coded as
Ⅰ
,
Ⅱ
,
Ⅲ
,
Ⅳ
,
Ⅴ
,
Ⅵ
and
Ⅶ
, respectively. The relative rate was detected by
using the approach proposed by Sarich and Wilson
(1973), the results indicated in Table 3. The results
showed that there were differences in the rate of
molecular evolution of ITS sequences among the
different clustering groups in
Buxus
. Comparative
analysis of ITS
-
1 sequences showed that the evolution
rate of group
Ⅰ
was the fastest one, with the signi-
ficant differences (P <0.01) from the group
Ⅲ
and
Ⅳ
,
followed by
Ⅲ
groups and the slowest evolution rate
was group
Ⅳ
, with no significant differences (P
<0.01) from the group
Ⅱ
,
Ⅲ
(P> 0.05). Likewise,
analysis of ITS
-
2 sequence showed that the fastest
evolution rate was group
ⅰ
, with significant differences
group
ⅲ
, followed by group
ⅳ
, the slowest evolution
rate was group
ⅲ
, with no significant difference.
Comprehensive analysis of whole ITS sequence pres-
ented that the fastest evolutionary rate was groups
ⅰ
,
followed by group
ⅲ
, the slowest evolution rate was
group
ⅳ
, all of them have reached a very significant
difference.
2 Discussions
Recently, there is yet considerable debates on the
relative relationship of between pearl boxwood (
Buxus
sinica
var.
parvifolia
) and
Buxus
sinica
as well as the
taxonomic status of pearl boxwood (
Buxus
sinica
var.
parvifolia
). Zheng (1980) thought that the both
belonged to the same plant species and further considered
Figure 1 Phylogenetic tree of genus based on the ITS sequences