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Evolution of MIR166 Gene Family in Land Plants

MIR166基因家族在陆生植物中的进化模式分析



全 文 :MIR166基因家族在陆生植物中的进化模式分析∗
赵旭耀1ꎬ2ꎬ 陈斯云1ꎬ 赵  磊1ꎬ 张雪梅1ꎬ 马朋飞1ꎬ 郭振华1∗∗
(1 中国科学院昆明植物研究所中国西南野生生物种质资源库ꎬ 云南 昆明  650201ꎻ 2 中国科学院大学ꎬ 北京  100049)
摘要: MicroRNA (miRNA) 是一类广泛存在于真核生物中的具有转录后水平调控功能的内源非编码小分
子 RNAꎮ 在植物中ꎬ miRNA通过对靶基因的剪切或沉默来实现对植物生命活动的调控ꎬ 它是基因表达调
控网络的重要组成部分ꎮ miR165 / 166 (miR166) 是陆生植物中最为古老的 MIRNA 家族之一ꎬ 它通过对 3
型同源异域型-亮氨酸拉链 (HD ̄ZIP III) 等靶标的调控ꎬ 在植物的众多发育时期起着关键的调控作用ꎮ
本文分析了 MIR166基因在陆生植物中的进化关系ꎬ 并对 MIR166在基部陆生植物小立碗藓 (Physcomitrella
patens) 中的复制及进化进行了研究ꎮ 此外ꎬ HD ̄ZIP III 蛋白是植物中重要的一类转录因子ꎬ miR166 对
HD ̄ZIP III基因的调控作用在陆地植物保守的存在ꎬ 本文对 HD ̄ZIP III 基因和 miR166 在进化中的相互作
用进行了初步的探讨ꎮ
关键词: miR166ꎻ MIRNA基因进化ꎻ 基因重复ꎻ HD ̄ZIP III转录因子
中图分类号: Q 75            文献标识码: A                文章编号: 2095-0845(2014)03-331-11
Evolution of MIR166 Gene Family in Land Plants
ZHAO Xu ̄Yao1ꎬ2ꎬ CHEN Si ̄Yun1ꎬ ZHAO Lei1ꎬ ZHANG Xue ̄Mei1ꎬ
MA Peng ̄Fei1ꎬ GUO Zhen ̄Hua1∗∗
(1 Germplasm Bank of Wild Species in Southwest Chinaꎬ Kunming Institute of Botanyꎬ Chinese Academy of Sciencesꎬ
Kunming 650201ꎬ Chinaꎻ 2 University of Chinese Academy of Sciencesꎬ Beijing 100049ꎬ China)
Abstract: MicroRNA (miRNA) is a class of endogenous non ̄coding small RNAs with important post ̄transcriptional
regulatory roles in eukaryotes. Plant miRNAs play important roles in the post ̄transcriptional regulatory network through
mediating cleavage or silencing of target mRNAs. As one of the ancient MIRNA familyꎬ miR165 / 166 (miR166) is a
key regulator in land plants. In this studyꎬ we analyzed the diversity and molecular evolution of MIR166 genes in land
plantsꎬ and identified the replication and evolution of MIR166 genes in Physcomitrella patens. Homeodomain Leucine ̄
zipper of class III (HD ̄ZIP III) proteins are important transcription factors in plantsꎬ HD ̄ZIP III genes are con ̄
served targeting of miR166 in angiospermsꎬ gymnospermsꎬ fernsꎬ and mosses. Hereꎬ a preliminary study was con ̄
ducted to make clear the relationships between HD ̄ZIP III genes and miR166 during the evolutionary process.
Key words: miR166ꎻ MIRNA gene evolutionꎻ gene duplicationꎻ HD ̄ZIP III transcription factors
  After the first miRNA gene ( lin ̄4) was identi ̄
fied in Caenorhabditis elegans (Lee et al.ꎬ 1993)ꎬ
more and more miRNAs were discovered in eu ̄
karyotes through deep sequencing and bioinformatics
植 物 分 类 与 资 源 学 报  2014ꎬ 36 (3): 331~341
Plant Diversity and Resources                                    DOI: 10.7677 / ynzwyj201413123

∗∗
Funding: The NSFC ̄Yunnan province joint foundation (U1136603)ꎻ the Knowledge Innovation Project of the Chinese Academy of Sciences
(KSCX2 ̄YW ̄N ̄067)ꎻ the National Natural Science Foundation of China (30990244)ꎻ Scientific Research Foundation for the
Returned Overseas Chinese Scholarsꎬ State Education Ministry and the Young Academic and Technical Leader Raising Foundation
of Yunnan Province (2008PY065)ꎻ the Western Light Talent Culture Project of the Chinese Academy of Sciences (2010312D11035)ꎻ
and the Yunnan Provincial Government through an innovation team programme
Author for correspondenceꎻ E ̄mail: guozhenhua@mail􀆰 kib􀆰 ac􀆰 cn
Received date: 2013-05-28ꎬ Accepted date: 2014-01-03
作者简介: 赵旭耀 (1987-) 男ꎬ 硕士ꎬ 从事生物信息与比较基因组学研究ꎮ E ̄mail: zhaoxuyao@mail􀆰 kib􀆰 ac􀆰 cn
approaches. Those MIRNA genes with significant se ̄
quence homology to each other when compared
based on mature miRNA sequences are grouped into
miRNA families (Ambros et al.ꎬ 2003). Hundreds
of miRNA families have been found in plantsꎬ but
most of them are lineage ̄specificꎬ suggesting that
most known MIRNA genes arose relatively recently in
evolutionary time scale ( Cuperus et al.ꎬ 2011 ).
There are only 8 families are deep conserved in land
plantsꎬ miR166 family is one of this kind (Nozawa et
al.ꎬ 2010).
miRNAs play important roles in various devel ̄
opmental and physiological processes ( Seed germi ̄
nationꎬ vegetative growingꎬ floweringꎬ seeding and
resistance to various abiotic or biotic stress) by tar ̄
geting mRNAs for cleavage or translational repres ̄
sion at the post ̄transcriptional level in the plants
kingdoms ( Reinhart et al.ꎬ 2002ꎻ Carrington and
Ambrosꎬ 2003). miR166 and its targets regulate an
array of plant developmental processesꎬ including
shoot apical and lateral meristem formationꎬ leaf po ̄
larityꎬ floral developmentꎬ and vascular development
(McConnell et al.ꎬ 2001ꎻ Otsuga et al.ꎬ 2001ꎻ
Prigge et al.ꎬ 2005ꎻ Jung and Parkꎬ 2007).
An increasing number of plant miRNA genes
have been discovered through experimental and
bioinformatic studies in plantsꎬ and they provide an
opportunity to study the origins and evolution of
them. There have been some evolutionary research
on miRNAs in animalsꎬ plants and some smaller lin ̄
eage (Li et al.ꎬ 2011ꎻ Hertel et al.ꎬ 2012ꎻ Zhao et
al.ꎬ 2012). The miRNAs in land plants are regarded
as deriving from a common ancestor ( Jones ̄Rhoad ̄
esꎬ 2012). Howeverꎬ it is unclear whether the miR ̄
NA pathway in green alga shares a common ancestry
with miRNA pathways of land plantsꎬ or whether it
is independently derived. There have not found a
miRNA conserved between land plants and algas
(Jones ̄Rhoadesꎬ 2012).
The previous research had revealed the evolu ̄
tionary history of the MIR166 homologs in Arabidop ̄
sis derived from duplication eventsꎬ including tan ̄
dem duplications and segmental duplication events
(Maher et al.ꎬ 2006). Thenꎬ Sun et al. (2012)
characterized the MIR166 genes derived from duplica ̄
tion events in riceꎬ sorghumꎬ and poplar. Those re ̄
searches indicating that duplication events are impor ̄
tant in the expansion of MIR166 genes in flowering
plants. In this studyꎬ we found the phenomenon is
exist in moss tooꎬ thenꎬ the overall phylogenetic tree
of miR166 in Physcomitrella patens was reconstruc ̄
ted base on the duplication events.
In addition to the duplication and loss events in
the genomeꎬ the targets of miRNA is another impor ̄
tant factor in the miRNA evolution. The “new” miR ̄
NAs only have a few suspected targets while the con ̄
served miRNAs target numerous important mRNAs
in the eukaryotes. In the evolutionary history of miR ̄
NAsꎬ the “ ancestor” miRNAs were subdivided into
hundreds of familiesꎬ and the miRNAs which cap ̄
ture important targets finally evolve to the conserved
multi ̄gene families ( Bompfunewerer et al.ꎬ 2005ꎻ
Hertel et al.ꎬ 2012). The mature miRNA sequence
is complementary to the mRNA targeted regionꎬ thus
the conserved target determine the conservative pro ̄
perty of miRNA. The gain of target mRNA can cause
the expansione or functional diversification of miR ̄
NAꎬ and the loss and pseudogene change of mRNA
can cause deletion or functional loss of miRNA.
In this studyꎬ we reconstructed the phylogenetic
tree of MIR166 genes in land plantsꎬ thenꎬ we iden ̄
tified the duplication events originated miR166 genes
in Physcomitrella patens and inferred their phyloge ̄
netic relationship. At lastꎬ the phylogenetic distribu ̄
tion of miR166 targeted ̄ HD ̄ZIP III in land plants
were constructed to study the interaction between
miR166 and HD ̄ZIP III.
1  Materials and methods
1􀆰 1  Phylogenetic analysis of MIR166 genes in
land plants
The mature sequences and precursor sequences
of miRNAs were downloaded from miRBase database
release 19 (http: / / www􀆰 mirbase􀆰 org / ) (Addition ̄
233                                  植 物 分 类 与 资 源 学 报                            第 36卷
al file 1ꎬ http: / / journal􀆰 kib􀆰 ac􀆰 cn / UserFiles / File /
ZXY􀆰 rar) . The LOGO representation of mature miR ̄
NAs was obtained with the WebLogo software
(Crooks et al.ꎬ 2004).
All of the stem ̄loop sequences of the miR166
family were aligned using Clustal W (Larkin et al.ꎬ
2007). Thenꎬ We excluded the incorrect aligned se ̄
quences in the conserved regions of miRNA: miR ̄
NA∗ and aligned the remaining sequences again.
Secondary structures were produced for each se ̄
quence in the alignment using RNAfold (Mohsen et
al.ꎬ 2009). Thenꎬ we used 4SALE to correct the a ̄
lignment manually by considering the agreement in
secondary structure ( Seibel et al.ꎬ 2006) and the
consensus sequences and structure using RNAalifold
(Bernhart et al.ꎬ 2008).
Neighbor ̄joining (NJ) phylogenetic trees based
on the p ̄distance and Kimura 2 ̄parameter distance
were generated by MEGA version 5􀆰 0 (Tamura et al.ꎬ
2011). Bootstrap confidence values were obtained ap ̄
plying by 1 000 replicationsꎬ and only the clades
with bootstrap value higher than 50 were shown.
1􀆰 2  Identification of miR166 homologues resides
in duplicated blocks in Physcomitrella patens
In order to determine whether the miRNAs a ̄
rose or evolved from segmental duplication eventsꎬ
genome ̄wide analysis was undertaken to examine
whether a miRNA resides within a duplicated block
as previously described (Zhang et al.ꎬ 2009ꎻ Sun et
al.ꎬ 2012). Firstꎬ we used NCBI map viewer (http:
/ / www􀆰 ncbi􀆰 nlm􀆰 nih􀆰 gov / projects / mapview / ) to ex ̄
tract 10 protein ̄coding genes in flanking regions for
each MIR166 homologues or tandemly duplicated
miR166 clusters. Then the flanking protein ̄coding
genes of every miRNA were alignedꎬ using standa ̄
lone BLAST (blastnꎬ version 2􀆰 2􀆰 27)ꎬ against those
protein ̄coding genes surrounding another miRNA in
order to identify paralogs. For each miRNA pairꎬ the
number of protein coding genes with the best non ̄self
match to protein ̄coding genes flanking another miR ̄
NA was counted (Sun et al.ꎬ 2012) (Additional file
2ꎬ http: / / journal􀆰 kib􀆰 ac􀆰 cn / UserFiles / File / ZXY􀆰
rar) . The flanking noncoding sequences were aligned
by Emboss to help resolve the evolutionary history of
the miR166 family (Rice et al.ꎬ 2000).
1􀆰 3  miR166 targeted ̄HD ̄Zip III in land plants
A total of 60 mRNA sequences of HD ̄Zip III
protein were downloaded from NCBI. Then 36 se ̄
quences from 9 plant species (Arabidopsis thalianaꎬ
Medicago truncatulaꎬ Oryza sativaꎬ Pinus taedaꎬ
Populus trichocarpaꎬ Ricinus communisꎬ Selaginella
moellendorffiiꎬ Solanum lycopersicumꎬ and Sorghum
bicolor) were collected for target prediction (Addi ̄
tional file 3ꎬ http: / / journal􀆰 kib􀆰 ac􀆰 cn / UserFiles /
File / ZXY􀆰 rar) . The miR166 ̄targeted HD ̄Zip III
mRNAs were predicted in psRNATarget under the
default rules (Dai and Zhaoꎬ 2011).
1􀆰 4  Phylogenetic analysis of HD ̄Zip III tran ̄
scription factor
Sequences of HD ̄Zip III mRNA were aligned
using CLUSTALXꎬ then MEGA version 5􀆰 0 was
used to construct neighbor ̄joining (NJ) and maxi ̄
mum likelihood (ML) tree. Supporting values were
assessed using 1000 replicate bootstrap tests.
2  Results
2􀆰 1  MIR166 is a diversity ancient miRNA gene
family that is ubiquitously distributed in flower ̄
ing plantsꎬ gymnospermsꎬ fernsꎬ and mosses
So farꎬ miRBase release 19 has collected a total
of 209 MIR166 genes of 35 species ranged from moss
to the higher plants ( Table 1). The precursor se ̄
quences of miR166 are diversified in land plantsꎬ
the longest precursor is 670nt and the shortest one is
72nt ( pvu ̄miR166 and sbi ̄miR166b). Howeverꎬ
the short functional mature sequence is highly con ̄
served in land plants. We also found that the mature
miRNA were sequence characterized in the different
lineages (Figure 1). MIR166 is a typical multiple ̄
gene familyꎬ and there are numerous paralogs in
many plants species ( miR166 is single copy in 7
plantsꎬ but it’s attribute to the lack of genome and
deeper research ). Evidences above indicate that
MIR166 is an old miRNA family in land plants. The
3333期                  ZHAO Xu ̄Yao et al.: Evolution of MIR166 Gene Family in Land Plants                   
features of miR166 precursors suggest that the
MIR166 genes have a complex evolution history.
Table 1  The distribution of miR166 in land plants
Clade Species
Number of
miR166
genes
Bryophyta Physcomitrella patens 13(13ꎬ0)
Fern Selaginella moellendorffii 3(1ꎬ2)
Picea abies 2(2ꎬ0)
 
Pinus densata 2(2ꎬ0)
Pinus taeda 2(2ꎬ0)
                                                                             
Brachypodium distachyon 7(5ꎬ2)
Hordeum vulgare 3(2ꎬ1)
Oryza sativa 14(8ꎬ6)
Sorghum bicolor 11(8ꎬ3)
Zea mays 14(12ꎬ2)
                                                                       
Arabidopsis lyrata 9(4ꎬ5)
Aquilegia coerulea 5(3ꎬ2)
Arabidopsis thaliana 9(4ꎬ5)
Brassica napus 6(4ꎬ2)
Cucumis melo 9(6ꎬ3)
Citrus reticulata 2(2ꎬ0)
Citrus sinensis 5(3ꎬ1)∗
Citrus trifoliata 1(0ꎬ0)∗
Digitalis purpurea 2(1ꎬ1)
 
Gossypium hirsutum 1(1ꎬ0)
Glycine max 21(6ꎬ15)
Hevea brasiliensis 2(2ꎬ0)
Helianthus paradoxus 1(1ꎬ0)
Helianthus petiolaris 1(0ꎬ1)
Malus domestica 9(4ꎬ5)
Manihot esculenta 1(0ꎬ1)
Medicago truncatula 8(6ꎬ2)
Nicotiana tabacum 8(3ꎬ5)
Populus trichocarpa 17(9ꎬ8)
Phaseolus vulgaris 1(0ꎬ0)∗
Ricinus communis 5(4ꎬ1)
Solanum lycopersicum 2(2ꎬ0)
Salvia sclarea 1(1ꎬ0)
Theobroma cacao 4(4ꎬ0)
Vitis vinifera 8(2ꎬ6)
The number in the bracket is type 1 and type 2 miR166 gene in this
speciesꎬ ∗ represent the miRNA genes with 5’ mature miRNAs
2􀆰 2  Evolution of MIR166 gene in land plants
Stem ̄loop sequences were usually applied to
study the phylogenetic relationship because they are
the most conserved parts of the miRNA genes (Li et
al.ꎬ 2011ꎻ Hertel et al.ꎬ 2012ꎻ Zhao et al.ꎬ 2012).
The selections for mutations in structured RNA
mainly arise from base ̄pairings to maintain the RNA
structures while in protein ̄coding sequences selec ̄
tion pressure disadvantages mutations in triplet codes
that disrupt protein functions through alteration of a ̄
mino ̄acids (Li et al.ꎬ 2011). As a class of func ̄
tional RNAꎬ structure character of pre ̄miRNA is
more important than its sequence character out of the
region of miRNA: miRNA∗ꎬ just as nonsense muta ̄
tion in the proteinꎬ the substitution don’ t cause
structural change in the stem ̄loop is non ̄significa ̄
tion mutation. So we construct the phylogenetic tree
of MIR166 using the structure and sequence charac ̄
ters of the stem ̄loop.
We aligned the stem ̄loop sequences of miR166ꎬ
three precursors with 5’ mature miRNA were exclu ̄
ded (Ambros et al.ꎬ 2003). Then we used RNAfold
to predicted their stem ̄loop structuresꎬ in this stepꎬ
we classified the pre ̄miR166 into two types accord ̄
ing to their structural conservation in the region of
loop (Figure 2)ꎬ type 1 pre ̄miR166 which have a
long stem with several mismatch bases and a loop is
canonical stem ̄loop structureꎬ and there are extra
loops in type 2 pre ̄miR166 cause by the abundant
mismatch in this region which may be induced by
nucleotide variation in the evolution history. Type 1
is the main form of pre ̄miR166 in land plantsꎬ all
the pre ̄miR166 in the base of land plants Physcomi ̄
trella patens are belong to type 1ꎬ and type 2 pre ̄
miR166 is a variation of type 1.
So we determined to use the 127 type 1 pre ̄miR166
to build the phylogenetic tree in land plantsꎬ the stem ̄
loop are divided into three space partitions in the
structure: miRNA: MIRNA∗ duplexesꎬ prolonged
stemꎬ and loop. The most conserved miRNA: MIR ̄
NA∗ duplexes region were retainꎬ in the prolonged
stems and loops which is cause by base pairing and
base mismatch respectivelyꎬ the sequence characters
of AUCG were translated into structure characters.
Thenꎬ we used RNAalifold to identify the consensus
sequences and structures of prolonged stems and
loops of pre ̄mir166 (Figure 3). At lastꎬ the structure
433                                  植 物 分 类 与 资 源 学 报                            第 36卷
Fig􀆰 1  RNA logo of mature miR166 in land plants
Sequence characterized of the mature miRNA in the different lineagesꎬ U / A at16nt in monocotsꎬ
U / C at 17nt in dicotsꎬ U / A at 13nt in the lineage of mossꎬ fern and gymnosperms
Fig􀆰 2  Structure of pre ̄miRNA
The stem ̄loop structure of pre ̄miRNA is divided into three partsꎬ the
part in green wireframe is miRNA: miRNA∗ duplexꎬ the part in pur ̄
ple wireframe is prolonged stemꎬ the part in red wireframe is loop. The
sequences of red is mature miRNA. Type 1 premiRNA in the left have
a typical stem ̄loop secondary structureꎬ and the premiRNA with a
complicated loop in the right is belongs to type 2
characters of prolonged stems and loops were transla ̄
ted into sequence characters based on the consensus
sequences and structures again (Additional file 4ꎬ
http: / / journal􀆰kib􀆰 ac􀆰 cn / UserFiles / File / ZXY􀆰 rar)ꎬ
the sequences of pre ̄miRNAs were aligned by Clust ̄
al W and then the NJ tree were constructed by
MEGA 5􀆰 0 (Figure 4).
    In the treeꎬ the homologous genes are highly
conserved in mossꎬ most of MIR166 genes show a
clustered tendency in monocotsꎬ they also have a
closer neighbor relationship to the moss. Howeverꎬ
their homologies in dicots showed a more diversified
evolutionary relationship. We speculate that the
MIR166 gene was originated in the original group
land plant just as moss. Thenꎬ the original seeding
plant inherited the gene and then hand down it to the
original Gymnosperm and flowering plants in the o ̄
rigination and evolution of flowering and seeding
plantsꎬ the ancestor of monocots should be appeared
before the dicots even the gymnosperm.
2􀆰 3  Evolutionary conservation analysis of miR166
homologues derived from duplication events in
P􀆰 patens
Gene duplications are derived from the duplica ̄
tion events which including whole ̄genome duplica ̄
tion (WGD)ꎬ segmental duplicationsꎬ and local du ̄
5333期                  ZHAO Xu ̄Yao et al.: Evolution of MIR166 Gene Family in Land Plants                   
Fig􀆰 3  The methods of construct phylogenetic tree of miRNA gene
The part in red is mature and star miRNA sequencesꎬ the part in green is the sequences of loop structureꎬ the part in black is the sequences
of prolonged stem. In step 1ꎬ the most conserved miRNA: MIRNA∗ duplexes region is removedꎬ the sequences of prolonged stems and loops
are retained. Thenꎬ the sequence characters of AUCG were translated into structure characters. After thatꎬ the consensus sequences and struc ̄
tures of prolonged stems and loops are identify. Nextꎬ the structure characters of prolonged stems and loops were translated into sequence char ̄
acters based on the consensus sequences and structures again. At lastꎬ the removed sequences of miRNA and miRNA∗ are restored
plications that involve one or two genes known as
tandem duplications (Maher et al.ꎬ 2006). The du ̄
plication events also contribute to expansion of miR ̄
NA familiesꎬ especially in the WGDꎬ some protein ̄
coding genes and TE will generate new miRNA
genes (Hertel et al.ꎬ 2006ꎻ Maher et al.ꎬ 2006ꎻ
Yuan et al.ꎬ 2011). Previous studies showed that
many plant MIRNAs are resided in the genomic du ̄
plication blocksꎬ the context sequencing of them and
them duplication is conserved to their repetition
(Sun et al.ꎬ 2012). So the flanking sequencesꎬ in ̄
cluding conserved coding genes and conserved non ̄
coding regions flanking can be used for identification
the MIRNA gene in duplicated blocks.
Maher et al. (2006) have studied the evolution
of duplication derived MIRNA165 / 166 in A􀆰 thalianaꎬ
in their researchꎬ the overall evolution of seven
miR166 members were reconstructed. Recent re ̄
search suggests ath ̄miR165a is origin from ath ̄
miR166b before the origin of ath ̄miR166aꎬ then a
base substitution is introduced into ath ̄miR165aꎬ in
the recent large large ̄scale duplication eventꎬ ath ̄
miR165b and ath ̄miR166a are originated from the
duplicated blocks of ath ̄miR165a and ath ̄miR166b
respectively. It’s in accordance with the results in
phylogenetic research aboveꎬ ath ̄miR165a and ath ̄
miR166b belong to type 1 MIR166 geneꎬ ath ̄
miR165b and ath ̄miR166b belong to type 2 MIR166
geneꎬ it’s also a evidence for that the type 2 MIR166
gene is originated from type 1 MIR166 gene.
As a genome sequenced plantꎬ the research of
miRNA in P􀆰 patens is concerned. Though P􀆰 patens
is a non ̄flowering plantꎬ several conserved miRNAs
exist in flowering plants were detected in moss.
miR166 is the one of the miRNAs which is found in
moss earliestꎬ Floyd and Bowman (2004) cloned a
HD ̄ZIP III gene homolog PpC3HDZIP1 which con ̄
tains a conserved miR166 ̄targerted region from
P􀆰 patensꎬ they also cloned a putative miR166 ̄
guided cleavage product of PpC3HDZIP1 mRNA.
The experiment indirectly demonstrates the exists of
miR166 in moss. In the next studyꎬ more and more
moss miRNA were detected with the availability of
P􀆰 patens genomesꎬ including 12 MIRNA166 genes
(Arazi et al.ꎬ 2005). The numerous homologies in
moss suggest that the expansion of miR166 is consid ̄
erable. Howeverꎬ as outlined aboveꎬ miR166 family
is more conserved in P􀆰 patens than other plants with
633                                  植 物 分 类 与 资 源 学 报                            第 36卷
many membersꎬ so we want to reveal the intraspecif ̄
ic evolution of miR166 in P􀆰 patens.
In this studyꎬ we analysed the context of
MIR166 genes in P􀆰 patens to seek their flanking
coding genes and noncoding sequencesꎬ those se ̄
quences were used to identify miR166 homology
genes origined from duplication block. Thenꎬ a total
of 9 duplication blocks around MIR166 genes were
obtained in P􀆰 patens (Table 2). There are 8 out of
13 miR166 loci were located in miRNA clusters
(ppt ̄miR166cdf clusterꎬ ppt ̄miR166ij clusterꎬ and
ppt ̄miR166hkm cluster)ꎬ the short length of three
miRNA clusters indicate at last one tachytelic evolu ̄
tion events of tandem duplications occurred in moss
genomeꎬ ppt ̄miR166m of the base substitution is or ̄
igin from ppt ̄miR166h or ppt ̄miR166k in a latter
tandem duplications event. On the other handꎬ the
clusters of miR166 suggest they provide stable and
conservative regulatory effect in the P􀆰 patens. Then
through the conserved flanking coding gene between
MIRNA166 genesꎬ we found that one flanking coding
gene of miR166e is conserved to two flanking coding
genes of the miR166ij clusterꎬ thenꎬ the higher con ̄
served stem ̄loop structure between miR166e and
miR166j indicted that miR166j is origin from the du ̄
plication block of miR166e before the tandem dupli ̄
cations event. There are two conserved flanking cod ̄
ing genes between ppt ̄miR166ij and ppt ̄miR166aꎬ
thenꎬ we found there are conserved noncoding se ̄
quences between ppt ̄miR166a and ppt ̄miR166ijꎬ
so we inferred that ppt ̄miR166a is a segmental du ̄
plication of ppt ̄miR166ij cluster before the loss e ̄
vent near the ppt ̄miR166a.
We also reconstruct the phylogenetic tree of
miR166 gene in the P􀆰 patens (Figure 5). In the treeꎬ
we found that the tandem duplications and segmental
duplications is frequently in the moss genomeꎬ it is
most likely to occur a large large ̄scale duplication e ̄
vent in the genome levelꎬ but we need more evi ̄
dence. The gene loss of miR166 in the moss is fre ̄
quent tooꎬ there are at least 3 loss events we known.
There is a replication block between ppt ̄miR166g Fig􀆰 4  The phylogenetic tree of type 1 premiR166
7333期                  ZHAO Xu ̄Yao et al.: Evolution of MIR166 Gene Family in Land Plants                   
Table 2  The number of conserved protein ̄coding genes
in the flanking the miR166
Duplicated
miRNAs 1
Duplicated
miRNAs 2
flanking conserved
protein ̄coding genes
ppt ̄miR166a ppt ̄miR166ij 2
ppt ̄miR166b ppt ̄miR166e 1
ppt ̄miR166b ppt ̄miR166g 1
ppt ̄miR166g ppt ̄miR166ij 1
ppt ̄miR166cdf ppt ̄miR166l 2
ppt ̄miR166e ppt ̄miR166ij 2
ppt ̄miR166e ppt ̄miR166l 1
ppt ̄miR166e ppt ̄miR166g 1
ppt ̄miR166ij ppt ̄miR166hkm 1
Fig􀆰 5  Reconstruction of miR166 evolution in Physcomitrella patens
Trigon is represent a segmental duplications eventꎬ
a circle is a tandem duplications event
and miR166eꎬ there also a replication block of ppt ̄
miR166h between ppt ̄miR ̄166i or ppt ̄miR166l.
Howeverꎬ the evolution details of ppt ̄miR166g and
ppt ̄miR166h is still unknown.
2􀆰 4  Phylogenetic distribution of miR166 targe ̄
ted ̄HD ̄ZIP III in land plants
Members of the Class III HOMEODOMAIN ̄
LEUCINEZIPPER transcriptional factors are plant ̄
specific and involved in many plant development
processes (Boualem et al.ꎬ 2008ꎻ Zhu et al.ꎬ 2011ꎻ
Sakaguchi and Watanabeꎬ 2012ꎻ Zhang et al.ꎬ
2012). The shoot apical meristem ( SAM) fate is
specified by HD ̄ZIP III transcriptional factors (Sak ̄
aguchi and Watanabeꎬ 2012). HD ̄ZIP III gene is
regulated by miR166: AGO1ꎬ in this processꎬ
AGO10 combined with miR166 competitively to re ̄
straint the negative regulation of HD ̄ZIP III gene
and maintenance of undifferentiated stem cells in the
SAM ( Liu et al.ꎬ 2009). HD ̄ZIP III gene and
MIR166 gene are present in many land plants because
they make an important contribution to maintain the
SAM and determine adaxial / abaxial polarity in plant
tissues. Negative regulation of HD ̄ZIP III by miR166
is highly conserved in land plantsꎬ and these HD ̄ZIP
III functions show diversity among different plant
groups (Sakaguchi and Watanabeꎬ 2012).
    Twenty ̄two out of 35 HD ̄Zip III genes were the
putative target genes for miR166 family with high
probability (Additional file 5ꎬ http: / / journal􀆰 kib􀆰
ac􀆰 cn / UserFiles / File / ZXY􀆰 rar) . The targeted re ̄
gion of HD ̄Zip III genes is very conserved in land
plants. We also built the phylogenetic tree of the
eight plants (Figure 6). There are two clades of HD ̄
Zip III genesꎬ all the P􀆰 patens HD ̄Zip III genes be ̄
long to clade 1ꎬ they shows considerable conserved
and it may be the reason to the evolutional characters
of ppt ̄miR166. HD ̄ZIP III protein is a key tran ̄
scription factorꎬ it seems to be conserved in the du ̄
plication eventsꎬ the more copy of HD ̄ZIP III is a
factor of expand of MIR166 gene. And the stability
function of HD ̄ZIP III restrict the conserved of
MIR166 gene.
3  Discussion
The evolutionary rate around the plant is dispro ̄
portionꎬ it’s more slower in the functional sequences
just as protein coding genes than the junk DNA as
pseudogene. MIRNA gene is a “special case” ꎬ the
overall evolutionary rate of MIRNA gene is approxi ̄
mate to pseudogene although it is transcribed into
mRNA ̄like RNA and generate a functional RNA
production finally. The evolutionary rate of the differ ̄
ent regions in MIRNA gene is vary drasticallyꎬ the
rate of mature and star miRNA is considerably lower
than other regionsꎬ the conservative property of ma ̄
ture sequences is higher than the miRNA∗ sequence
833                                  植 物 分 类 与 资 源 学 报                            第 36卷
for the mature miRNA are essential to recognize tar ̄
get mRNAs as well as to make a duplex structure
with star sequencesꎬ whereas star sequences appear
to be essential only for keeping the duplex structure
with mature sequences (Nozawa et al.ꎬ 2010).
Individual miRNAs are much more evolutionary
labileꎬ the expansion or loss is frequentlyꎬ thenꎬ the
incongruous conservative property between mature
sequence and precursor sequence increase the diffi ̄
culty to understand the overall evolutionary of those
miRNA gene as MIR166 through the traditional
methods. The structure character is useful to the evo ̄
lution research in the MIRNA genes.
Howeverꎬ the surrounding conserved coding
genes sequences of MIRNA gene with normal evolu ̄
tionary ratesꎬ the duplication events and evolutional
of them could be traced. So the evolution of the con ̄
served flanking protein ̄coding gene and non ̄coding
sequences give a track to the evolutional history of
miRNAs in the same duplication blocks. The arising
of their homologues gene always be associated to the
duplications events in the genomeꎬ it can contribute
Fig􀆰 6  Phylogenetic distribution of HD ̄ZIP III genes in land plants. The miR166 targeted ̄ HD ̄ZIP III genes are signed in yellow
9333期                  ZHAO Xu ̄Yao et al.: Evolution of MIR166 Gene Family in Land Plants                   
to the research of the evolution in a smaller lineage.
In reconstructing of the evolution history of
MIR166 genesꎬ the structure characteristics of pre ̄
miR166 were taken into account tentatively and we
acquired believable results. We hope miRNAs could
be used as the phylogeny markers in the future.
Acknowledgments: We thank Dr. Wei Jiang (Kunming In ̄
stitute of Botanyꎬ Chinese Academy of Sciences) and Pro.
Berezikov (Hubrecht Instituteꎬ KNAW and University Medi ̄
cal Center Utrecht) for their constructive advices.
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Additional file
Additional file 1. The sequences and structures of type 1 premiR166.
Additional file 2. The number of conserved protein ̄coding genes in the flanking the miR166.
Additional file 3. mRNA sequences of HD ̄ZIP III we used for target prediction.
Additional file 4. The premiR166 sequences processed through the structure character.
Additional file 5. miR165 / 166 targeted ̄HD ̄ZIP III genes in land plants.
􀳋 􀳋 􀳋 􀳋 􀳋 􀳋 􀳋 􀳋 􀳋 􀳋 􀳋 􀳋 􀳋 􀳋 􀳋
〔上接第 296页〕
华南植物研究所早期史———中山大学农林植物研究所史事 (1928-1954)ꎬ 中国近世生物学机构与人
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的胡先骕 (长江文艺出版社ꎬ 2005)、 静生生物调查所史稿 (山东教育出版社ꎬ 2005)、 胡先骕先生年
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的让人赞叹不已! 不要说自学成才了ꎬ 就是我等专业人士也自愧不如ꎮ
马金双 (邮箱: jinshuangma@gmail􀆰 com)
2014年 4月 15日星期二于上海松江 
1433期                  ZHAO Xu ̄Yao et al.: Evolution of MIR166 Gene Family in Land Plants