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Analyses of the UBX Protein Family in Populus and Vitis

杨树和葡萄UBX蛋白质家族分析



全 文 :杨树和葡萄 UBX蛋白质家族分析∗
刘德团1∗∗ꎬ 曹  军2∗∗ꎬ 许  琨1∗∗∗
(1 中国科学院昆明植物研究所丽江森林生态系统定位研究站ꎬ 云南 昆明  650201ꎻ
2 江苏大学生命科学学院ꎬ 江苏  212013)
摘要: UBX (泛素调控 X因子) 蛋白质家族在泛素化相关的过程中起着重要的作用ꎬ 如细胞周期调控、
转录调控、 信号转导、 发育、 胁迫响应、 细胞程序性死亡、 内吞作用和 DNA 修复ꎮ 然而ꎬ 到目前为止ꎬ
UBX家族在杨树和葡萄中还没有被研究过ꎮ 为了更好的弄清这两个植物的 UBX家族ꎬ 我们对 UBX的基因
结构、 染色体位置、 基因重复、 系统发育关系作了分析ꎮ 该研究对葡萄和杨树的 UBX 蛋白质家族作了第
一个系统的分析ꎮ 基因的外显子 /内含子结构和蛋白质基序组成在同一个组里相对比较保守ꎮ 基因重复分
析表明ꎬ 串联重复和片段重复对于杨树和葡萄的 UBX基因家族的扩张有一定贡献ꎬ 基因缺失在 UBX基因
家族的扩张过程中也发生了作用ꎮ 本研究为 UBX蛋白质功能的研究奠定了基础ꎮ
关键词: 泛素调控 X因子ꎻ 基因结构ꎻ 基因重复ꎻ 系统发育
中图分类号: Q 75            文献标识码: A                文章编号: 2095-0845(2014)03-349-09
Analyses of the UBX Protein Family in Populus and Vitis
LIU De ̄Tuan1∗∗ꎬ CAO Jun2∗∗ꎬ XU Kun1∗∗∗
(1 Lijiang Alpine Botanic Gardenꎬ Kunming Institute of Botanyꎬ Chinese Academy of Sciencesꎬ Kunming 650201ꎬ Chinaꎻ
2 Institute of Life Sciencesꎬ Jiangsu Universityꎬ Jiangsu 212013ꎬ China)
Abstract: The UBX (Ubiquitin regulatory X) protein family plays important roles in ubiquitin ̄related processes in ̄
cluding cell ̄cycle controlꎬ transcriptional regulationꎬ signal transductionꎬ developmentꎬ stress responseꎬ pro ̄
grammed cell deathꎬ endocytosis and DNA repair. Howeverꎬ this family has not been studied to date in Populus and
Vitis. To better understand the UBX in these two plantsꎬ relevant analyses about gene structureꎬ chromosomal loca ̄
tionꎬ duplicationꎬ phylogenetic relationships were performed. Our study provides the first systematic analysis of the
Vitis and Populus UBX proteins. The exon / intron gene structure and motif composition were relatively conserved in
the same group. Duplication analyses suggested that tandem duplication and segmental duplication contribute to the
expansion of Populus and Vitis UBX gene familyꎬ while some gene loss has also occurred. The results presented basic
information on UBX proteinsꎬ which may show a scaffold for future functional analysis of this family.
Key words: UBXꎻ Gene structureꎻ Gene duplicationꎻ Phylogeny
  As sessile organismsꎬ plant growthꎬ develop ̄
ment and distribution are often affected by environ ̄
mental and endogenous signalsꎬ such as plant hor ̄
mones and stress. On the one handꎬ environmental
stimuliꎬ including coldꎬ heatꎬ droughtꎬ high salinity
and damage stimulusꎬ can seriously affect plant
growth and productivity worldwide (Boyerꎬ 1982).
On the other handꎬ plant hormonesꎬ which include
auxinꎬ the gibberellins (GAs)ꎬ abscisic acid (ABA)ꎬ
and so onꎬ also participate in regulating plant growth
植 物 分 类 与 资 源 学 报  2014ꎬ 36 (3): 349~357
Plant Diversity and Resources                                    DOI: 10.7677 / ynzwyj201413146

∗∗
∗∗∗
Funding: The “Strategic Priority Research Program” of the Chinese Academy of Sciences (XDA05050206)
The co ̄first author
Author for correspondenceꎻ E ̄mail: xukun@mail􀆰 kib􀆰 ac􀆰 cn
Received date: 2013-07-02ꎬ Accepted date: 2013-08-20
作者简介: 刘德团 (1984-) 男ꎬ 主要从事植物学相关研究ꎮ
and development (Grayꎬ 2004).
Proteins in cells keep in a continuous metabo ̄
lism process of degradation and updateꎬ which is es ̄
sential for the normal life function. Ubiquitin is an
evolutionarily highly conserved small proteinꎬ which
plays important roles in plant hormone synthesis and
signaling cascades process ( Dreher and Callisꎬ
2007). The ubiquitin system controls the selective
degradation of many short ̄lived regulatory proteins in
eukaryotic cellsꎬ which plays an important role in
cell ̄cycle controlꎬ transcriptional regulationꎬ signal
transductionꎬ developmentꎬ vesicular trafficꎬ stress
responseꎬ DNA repairꎬ programmed cell death and
so on (Hershko and Ciechanoverꎬ 1998). The pivot ̄
al role of the selective degradation process controlled
by ubiquitin protein has increasingly gained the at ̄
tention of researchers. The regulation of ubiquitin in
such a variety of cellular processes relies on the in ̄
teraction with its distinct binding specificities and ef ̄
fector functions. Consequentlyꎬ more and more ubiq ̄
uitin associated proteins that contain ubiquitin ̄bind ̄
ing domain have been identified ( Buchbergerꎬ
2002).
UBX domain (PF00789ꎬ pfam) is an 80 amino
acid residue moduleꎬ which is proved to be present
typically at the carboxyl terminus of many kinds of
eukaryotic proteins ( http: / / pfam􀆰 sanger􀆰 ac􀆰 uk / ) .
The UBX family is more structurally homologous to
ubiquitin than other members of the ubiquitin clan
( Buchberger et al.ꎬ 2001). Recent research re ̄
vealed that the highly conserved AAA ATPase p97
in yeast participates in ubiquitin ̄dependent proteoly ̄
sis (Ghislain et al.ꎬ 1996). P97 was thought to be a
molecular chaperone which is a key component in
the ubiquitin ̄proteasome system. This function is de ̄
pendent on association with cofactors ( Schuberth
and Buchbergerꎬ 2008ꎻ Kloppsteck et al.ꎬ 2012).
UBX domain containing proteins are mainly the co ̄
factors of p97 (Schuberth and Buchbergerꎬ 2008).
Ubx2ꎬ a transmembrane proteinꎬ participated in En ̄
doplasmic Reticulum ̄associated degradation (ERAD)
processꎬ which selectively transports the misfolded
proteins from the endoplasmic reticulum to the cyto ̄
plasm for further ubiquitylation and degradation
(Römischꎬ 2006) (Schuberth and Buchbergerꎬ 2005).
SAKS1ꎬ a UBX domain containing adaptor for p97ꎬ
can negatively modulate ERAD and p97 ̄dependent
degradation (LaLonde and Bretscherꎬ 2011). Ubx2 /
Ubxd8 regulates lipid droplet homeostasis ( Wang
and Leeꎬ 2012). Another UBX domain ̄containing
proteinꎬ TUG can also regulate the p97 ATPase
(Orme and Boganꎬ 2012). All above suggest an im ̄
portant role of UBX involved in processes including
protein degradationꎬ endocytosis and so on (Buch ̄
berger et al.ꎬ 2001).
Howeverꎬ only very few UBX domain proteins
have been studied up to now. A lot of researchers
have thoroughly studied other gene families in Popu ̄
lus or in Vitis. But they have not studied UBX family
in Populus or in Vitis. Few information about UBX
family in woody plant species such as Populus tricho ̄
carpa (poplar) and Vitis vinifera (grape) have been
commended.
In this studyꎬ the UBX proteins were analyzed
in silico for gene structureꎬ chromosomal locationꎬ
phylogenetic relationshipsꎬ protein sequence motifsꎬ
gene duplication in Populus and Vitis. We aimed to
better understand the evolution of UBX in these
plants. Our results show that the gene structure and
motif composition were highly conserved in the same
groupꎬ and tandem duplication and segmental dupli ̄
cation contribute to the expansion of Populus and Vi ̄
tis UBX gene familyꎬ while some gene loss has also
occurred. These will provide a fundamental basis for
further functional investigations on these proteins.
1  Methods
1􀆰 1  Sequence retrieval and identification
To identify potential members of the UBX pro ̄
tein family in Populus and Vitisꎬ we performed multi ̄
ple database searches. Arabidopsis UBX proteins
were obtained from the TAIR database ( http: / /
www􀆰 arabidopsis􀆰 org / ) The UBX protein number
present in the Arabidopsis was reported to be 15
053                                  植 物 分 类 与 资 源 学 报                            第 36卷
(Bednarekꎬ 2009). Additional searches were also
performed based on keyword “ UBX”ꎬ “ Ubiquitin
regulatory X”. Arabidopsis UBX protein sequences
were retrieved and used as queries in blastp searches
against the Poplar Genome database (http: / / genome􀆰
jgj ̄psf􀆰 org) and the Genoscope Grape Genome data ̄
base ( http: / / www􀆰 cns􀆰 fr) . Blastp searches were
also performed against the Poplar and Grape genomes
at Phytozome 7􀆰 0 (http: / / www􀆰 phytozome􀆰 net). To
perform a thorough search of UBX proteinsꎬ HMMER
version 3􀆰 0 (http: / / hmmer􀆰 janelia􀆰 org / ) was used to
perform searches against the entire protein set.
SMART (Simple Modular Architecture Research
Toolꎬ http: / / smart􀆰 embl ̄heidelberg􀆰 de / ) and Pfam
(http: / / pfam􀆰 sanger􀆰 ac􀆰 uk / ) were used to ensure
the presence of UBX domain (Punta et al.ꎬ 2012).
To estimate the isoelectric point (pI) and grand av ̄
erage hydropathy (GRAVY) valuesꎬ ProtParam tool
from ExPASy (http: / / us􀆰 expasy􀆰 org / tools / protparam􀆰
html) was used.
1􀆰 2  Phylogenetic analyses of the UBX protein
family
The software MEGA 5 (Tamura et al.ꎬ 2011)
was used to construct the phylogenetic tree in this
study. The amino acid sequences were first aligned
using the MUSCLE program with default parameters
in this softwareꎬ followed by manual comparisons
and refinement. Gaps and ambiguously aligned re ̄
gions were removed before phylogenetic analyses. A
neighbor ̄joining phylogenetic tree based on the a ̄
lignment described above was generated with p ̄dis ̄
tance model and the method of pairwise deletion of
gaps. Bootstrap replicates (1000) were used to eva ̄
luate the significance of each node of the tree. Other
options were default. The phylogenetic tree was dis ̄
played using MEGA software.
1􀆰 3  Chromosomal location and gene structure
of the UBX proteins
The chromosomal locations of the UBX proteins
were determined using the Populus genome browser
http: / / www􀆰 phytozome􀆰 net / poplar and Vitis genome
browser http: / / www􀆰 genoscope􀆰 cns􀆰 fr / spip / Vitis ̄
vinifera ̄e􀆰 html. Fig􀆰 2 and Fig􀆰 3 were drawn accord ̄
ing to the chromosome size and the position of UBX
genes. We just used the figures of the references so
we can easily see whether UBX is located in segmen ̄
tal blocks (Jaillon et al.ꎬ 2007ꎻ Licausi et al.ꎬ 2010ꎻ
Tuskan et al.ꎬ 2006). Gene intron / extron structure
information was collected from the genome annota ̄
tions of Populus and Vitis from NCBI and Phytozome
databases (7􀆰 0ꎬ http: / / www􀆰 phytozome􀆰 net). Gene
structure display server program (GSDSꎬ http: / / gs ̄
ds􀆰 cbi􀆰 pku􀆰 edu􀆰 cn / index􀆰 php) was used to display
the UBX gene structures by comparison of the full ̄
length cDNA sequences with the corresponding ge ̄
nomic DNA sequences (Guo et al.ꎬ 2007). Because
cDNA sequences are obtained from the correspond ̄
ing databasesꎬ which are already full ̄length cDNA.
1􀆰 4  Estimation of duplication time
Paralogous alignments were performed using
ClustalW (codons) in Mega 5. K ̄Estimator 6􀆰 0 was
used to estimate the Ka and Ks values of the paralo ̄
gous genes. And then the Ks was used to estimate the
approximate date of the duplication event. That is
T =Ks / 2λꎬ where λ represent clock ̄like rates of syn ̄
onymous substitution. For Populusꎬ λ=9􀆰 1×10-9 was
used (Lynch and Coneryꎬ 2000)ꎬ and 6􀆰 5×10-9 for
Vitis (Gaut et al.ꎬ 1996).
1􀆰 5  Conserved motifs analyses and sequence logo
Multiple Expectation Maximization for Motif
Elicitation (MEMEꎬ Version 4􀆰 9􀆰 0ꎬ http: / / meme􀆰
sdsc􀆰 edu) tool was used to identify motifs constitu ̄
tion in Populus and Vitis UBX protein sequences
(Bailey et al.ꎬ 2006). MEME was run locally with
the following parameters: Distribution of motif occur ̄
rences: Any number of repetitionsꎻ Number of dif ̄
ferent motifs: 30ꎻ Minimum motif width: 6ꎻ Maxi ̄
mum motif width: 200.
2  Results and discussion
2􀆰 1  Identification of the UBX protein family in
Populus and Vitis
To identify potential members of the UBX pro ̄
tein family in Populus and Vitisꎬ Arabidopsis UBX
1533期              LIU De ̄Tuan et al.: Analyses of the UBX Protein Family in Populus and Vitis                 
prtoteins were used as queries in blastp searches a ̄
gainst the Populus Genome database and the Vitis
Genome database. Sequences returned were identi ̄
fied with SMART and Pfam tools. The UBX protein
number present in the Arabidopsis was reported to be
15 ( Bednarekꎬ 2009). Twenty ̄three UBX proteins
were identified in Populus (Table 1) and 10 in Vitis
(Table 2). The UBX proteins in Vitis and Populus
range from 165 to 738 amino acids in length. The iso ̄
electric point ( pI) in Populus ranged from 4􀆰 58 to
9􀆰 78ꎬ and 4􀆰 81 to 6􀆰 22 in Vitis. The grand average
hydropathy (GRAVY) value is -0􀆰 807 to -0􀆰 245 in
Populus and -0􀆰 739 to -0􀆰 436 in Vitis respectively.
Lower GRAVY values indicate that they are soluble.
2􀆰 2  Phylogenetic analyses of the UBX proteins
in Arabidopsisꎬ Populus and Vitis
In order to investigate the evolutionary relation ̄
ships of the UBX proteins in Arabidopsisꎬ Populus
Table 1  UBX genes identified in Populus
Gene name Gene ID Location: chr: start ̄end (strand) Locus name Protein length PI GRAVY
popUBX1 7479342 scaffold_1: 6752650-6757124 (+) PUBXR_0001s08840 592 4􀆰 76 -0􀆰 753
popUBX2 7467049 scaffold_1: 8688279-8691670 (+) PUBXR_0001s11200 473 5􀆰 04 -0􀆰 264
popUBX3 7456202 scaffold_1: 23043626-23044670 (+) PUBXRDRAFT_844989 165 9􀆰 78 -0􀆰 245
popUBX4 7480069 scaffold_1: 26097804-26099520 (+) PUBXR_0001s27170 229 6􀆰 46 -0􀆰 575
popUBX5 7494211 scaffold_1: 34653537-34654649 (+) PUBXR_0001s36150 176 9􀆰 51 -0􀆰 319
popUBX6 7496891 scaffold_2: 18119451-18121869 (-) PUBXR_0002s21600 429 5􀆰 2  -0􀆰 694
popUBX7 7489882 scaffold_2: 19060655-19062952 (+) PUBXRDRAFT_711401 254 5􀆰 57 -0􀆰 471
popUBX8 7465837 scaffold_3: 12879636-12884009 (+) PUBXR_0003s12230 589 4􀆰 58 -0􀆰 779
popUBX9 7497510 scaffold_3: 14581207-14584774 (+) PUBXR_0003s14510 474 5􀆰 06 -0􀆰 29 
popUBX10 7492568 scaffold_4: 222264-226984 (-) PUBXR_0004s00590 305 5􀆰 52 -0􀆰 64 
popUBX11 7492568 scaffold_4: 236182-238326 (+) PUBXR_0004s00620 218 5􀆰 24 -0􀆰 616
popUBX12 7491781 scaffold_7: 1416610-1421004 (+) PUBXR_0007s02410 520 5􀆰 6  -0􀆰 586
popUBX13 7482908 scaffold_8: 8746906-8751006 (+) PUBXR_0008s13320 480 6􀆰 28 -0􀆰 57 
popUBX14 7457839 scaffold_8: 9414593-9422375 (+) PUBXR_0008s14230 455 4􀆰 89 -0􀆰 526
popUBX15 7482291 scaffold_9: 6203578-6205202 (+) PUBXR_0009s06420 250 6􀆰 61 -0􀆰 472
popUBX16 7462631 scaffold_10: 11284948-11292772 (-) PUBXR_0010s10910 451 4􀆰 98 -0􀆰 525
popUBX17 7484509 scaffold_11: 357597-358981 (+) PUBXR_0021s00560 253 5􀆰 36 -0􀆰 406
popUBX18 7484546 scaffold_11: 1135741-1138580 (-) PUBXR_0011s01620 305 5􀆰 32 -0􀆰 581
popUBX19 7496924 scaffold_14: 5422940-5428222 (+) PUBXR_0014s07170 464 5􀆰 62 -0􀆰 713
popUBX20 7462075 scaffold_14: 11585957-11588052 (-) PUBXR_0014s15560 408 5􀆰 11 -0􀆰 659
popUBX21 7453782 scaffold_15: 10460579-10463003 (-) PUBXR_0015s09180 401 8􀆰 07 -0􀆰 505
popUBX22 7463293 scaffold_17: 4926068-4932450 (+) PUBXR_0017s06430 543 5􀆰 69 -0􀆰 592
popUBX23 7457047 scaffold_Un: 2571-4878 (-) PUBXRDRAFT_792398 409 5􀆰 33 -0􀆰 807
Table 2  UBX genes identified in Vitis
Gene name Gene ID Location: chr: start ̄end (strand) Locus name Protein length PI GRAVY
vitUBX1 100247740 chr1: 2244794-2294793 (-) GSVIVG01010276001 456 4􀆰 81 -0􀆰 525
vitUBX2 100257839 chr1: 5295143-5301096 (-) GSVIVG01011678001 474 6􀆰 22 -0􀆰 438
vitUBX3 100263375 chr2: 2079818-2091015 (+) GSVIVG01019629001 354 5􀆰 24 -0􀆰 482
vitUBX4 100251323 chr2: 3558065-3566452 (-) GSVIVG01019815001 738 4􀆰 84 -0􀆰 739
vitUBX5 100244691 chr5: 21017108-21042799 (-) GSVIVG01013567001 542 5􀆰 25 -0􀆰 599
vitUBX6 100262315 chr10: 111796-117184 (+) GSVIVG01004812001 299 5􀆰 47 -0􀆰 636
vitUBX7 100261938 chr10: 120527-137361 (-) GSVIVG01004815001 428 5􀆰 79 -0􀆰 559
vitUBX8 100243031 chr12: 6128660-6135333 (-) GSVIVG01030489001 366 4􀆰 97 -0􀆰 477
vitUBX9 100249155 chr14: 26293468-26297939 (-) GSVIVG01001850001 231 5􀆰 77 -0􀆰 533
vitUBX10 100241512 chr17: 10309381-10311030 (-) GSVIVG01007694001 335 5􀆰 86 -0􀆰 436
253                                  植 物 分 类 与 资 源 学 报                            第 36卷
and Vitisꎬ we constructed a neighbor ̄joining phylo ̄
genetic tree from a multiple sequence alignment of
full length UBX proteins using Mega 5. Based on the
bootstrap valuesꎬ gene structure and conserved mo ̄
tifꎬ we further divided them into seven subgroupsꎬ
namely Groups 1-7 (Fig􀆰 1).
Each group contains all the three speciesꎬ which
suggested that some ancestor UBX genes had
branched before species evolved into woody plant
and herbarium lineages. In a single homologsꎬ which
can be called as homologousꎬ most Populus UBXs
clustered with their homologous in Populus (Populus
-Populus)ꎬ sometimes clustered together with a grape
UBX (Populus-Vitis)ꎬ but never clustered together
Fig􀆰 1  Phylogenetic relationshipsꎬ gene structure and conserved motif of UBX proteins in Arabidopsis (at)ꎬ Populus (pop) and Vi ̄
tis (vit) . The molecular phylogeny ( left panel) was constructed using full length UBX protein sequences from the three species.
Numbers associated with branches show bootstrap support values for neighbor ̄joining (NJ) analyses. The 7 major groups designated
from 1 to 7 are marked with different color backgrounds. Exon / intron structures of the UBX genes are shown in the middle panel. The
long intron was denoted by “ / / ” . Green boxes represent exons and black lines represent introns. A schematic representation of con ̄
served motifs (obtained using MEME) in UBX proteins is displayed on the right panel. Different boxes represent different motifs
3533期              LIU De ̄Tuan et al.: Analyses of the UBX Protein Family in Populus and Vitis                 
with any corresponding protein in Arabidopsis (Popu ̄
lus≠Arabidopsis). It’s the same to grapeꎬ in a sin ̄
gle homologsꎬ grape UBXs clustered together with
grape UBXs (Vitis-Vitis)ꎬ sometimes clustered to ̄
gether with a single Populus protein (Populus -Vi ̄
tis)ꎬ but never clustered together with any protein in
Arabidopsis ( Populus ≠ Arabidopsis ). It indicated
that some UBX proteins may have evolved after the
woody plant and herbs differentiation.
2􀆰 3   Exon ̄intron evolution of the UBX family
genes in Arabidopsisꎬ Populus and Vitis
The exon / intron structure can provide new clues
for our further understanding the evolutionary mecha ̄
nisms underlying the origin of family genes (Chen et
al.ꎬ 2012). So a comparison between the cDNA and
genomic sequences were conducted in Arabidopsisꎬ
Populus and Vitis. Fig􀆰 1 illustrated the distribution
and position of exons / introns within each of the UBX
genes. Generallyꎬ intron loss / gain events are impor ̄
tant mechanism generating structural diversity and
complexityꎬ while the structural diversity may be a
mechanism for the gene family expansion (Cao et al.ꎬ
2011). In this studyꎬ we analyzed the structural di ̄
versity of UBX proteins and found that exon / intron
loss or gain events occurred during the expansion and
structural evolution of UBX paralogous. The family
proteins in the same group have similar exon / intron
structures ( include intron number or exon lengthꎬ
Fig􀆰 1)ꎻ which better support their close phylogeny
relationship. For instanceꎬ the UBX genes in each
group contained at least two introns with exception of
atUBX5 in group 2 and popUBX4ꎬ popUBX15 in
group 7ꎬ which had no introns. In contrast to other
members in group 7ꎬ a gene having simple gene
structure and the same function may be an advanced
kind of evolved form. Different gene structures in the
different phylogenetic subgroups can be a clue of
gene family expansion from ancient paralogous or a
clue of multiple origins of gene ancestry.
2􀆰 4   Chromosomal location and duplication of
the UBX proteins
To further study the gene duplication mecha ̄
nism in the Populus and Vitis genomesꎬ we mapped
the UBX gene onto chromosome. The chromosomal
location of UBX illustrated as Fig􀆰 2 (Populus) and
Fig􀆰 3 ( Vitis). As presented in Fig􀆰 2ꎬ we found
these UBX genes are distributed unevenly among
twelve chromosomes of the Populus genome. Chromo ̄
somes 5ꎬ 6ꎬ 12ꎬ 13ꎬ 16ꎬ 18 and 19 had no UBXꎬ
while relatively high densities of UBXs located on
chromosome I. PopUBX23 localized to unknown ge ̄
nomic sequence scaffolds and thus could not be
mapped to any particular chromosome.
Chromosomal segments duplicationꎬ tandem du ̄
plication and transposition events are three factors
result in family gene expansion ( Cannon et al.ꎬ
2004ꎻ Kong et al.ꎬ 2007). Study of Tuskan et al.
(2006) has identified the segmental duplication e ̄
vent in the Salicaceae (salicoid duplication) caused
the duplicated paralogous and significantly contribu ̄
ted to the expansion of plenty of gene families. Illus ̄
trated as Fig􀆰 2ꎬ it was found that 95% (21 / 22)
UBX genes are located in duplicated blocks except
for popUBX5. Two duplicated paralogous pairs
(popUBX ̄1 / 8 and popUBX ̄14 / 16) are located in
paralogous segment blocksꎬ so they can be the direct
results of the segmental duplication event. Two du ̄
plicated paralogous pair ( popUBX 2 ̄9ꎬ 4 ̄15ꎬ 17 ̄
18) located on the blocksꎬ but the position of corre ̄
sponding block shiftꎬ which suggested that dynamic
transposition events may have occurred after the seg ̄
mental duplication. Five duplicated UBX (popUBX ̄
12ꎬ 13ꎬ 19ꎬ 21ꎬ 20) also located on the blocksꎬ
but lacked duplicated parologous on the correspon ̄
ding blockꎬ suggesting that either the genes losses or
transposition may have occurred. According to phylo ̄
genetic resultꎬ several pairs of UBX proteins can be
considered as putative paralogous ( Fig􀆰 1). So we
computed the duplication time of these paralogous
according to Ks. These putative paralogous UBX pro ̄
teins account for 17􀆰 4% of all the UBX family in
Populus. As table 3 illustratedꎬ the duplication events
of these UBX in Populus occurred from 10􀆰 2Ma to
14􀆰 59Ma. This period is consistent with the time about
453                                  植 物 分 类 与 资 源 学 报                            第 36卷
Fig􀆰 2  Chromosomal locations of the Populus UBX protein family. The schematic diagram shows the 22 UBX proteins mapped to 12
chromosomes. One remaining genes (popUBX23) is located on unassembled scaffolds. Homologous blocks derived from
segmental duplication are indicated using the same colors according to Tuskan et al. (2006)
13Ma ago when large ̄scale genome duplication event
has occurred in Populusꎬ which suggest that large
scale gene loss has occurred after the large scale ge ̄
nome duplication event in Populus. For Vitisꎬ the
segmental duplication event of vitUBX6 / 7 was esti ̄
mated to occur in 11􀆰 78Ma.
Furthermoreꎬ the tandem duplications also con ̄
tribute to the expansion of UBX gene family (popUBX ̄
10 / 11). And popUBX22 was located on segmental
duplicate blocks with its counterpart popUBX23 not
mapped to any chromosome yet. Altogetherꎬ the seg ̄
ment duplicationꎬ tandem duplication and maybe
transposition eventsꎬ contributed to the expansion of
UBX gene family in the Populus UBX genome.
And as illustrated in Fig􀆰 3ꎬ the result showed
that the UBX genes are dispersed randomly through ̄
out the seven chromosomes of Vitis. Chromosomes 3ꎬ
4ꎬ 6ꎬ 7ꎬ 8ꎬ 9ꎬ 11ꎬ 13ꎬ 15ꎬ 16ꎬ 18 and 19 had no
Fig. 3   Chromosomal locations of the Vitis UBX family. The 10 UBX
proteins mapped to the 8 of the 19 grape chromosomes are shown.
Paralogous regions in the putative ancestral constituents of the
Vitis genome are depicted using the colors according to
Jaillon et al. (2007) and Licausi et al. (2010)
5533期              LIU De ̄Tuan et al.: Analyses of the UBX Protein Family in Populus and Vitis                 
Table 3  Estimation of duplication time
Ka Ks time (Ma)
popUBX14 / 16 0􀆰 0522  0􀆰 26546 14􀆰 59
popUBX1 / 8 0􀆰 08218 0􀆰 18562 10􀆰 2 
vitUBX6 / 7 0􀆰 06831 0􀆰 15309 11􀆰 78
UBX. We found that some UBX proteins are located
in tandem clusters on the chromosomesꎻ examples
are vitUBX6 ̄7 ( Fig􀆰 3). Tandem duplications may
also be a factor contributing to the genesis of family
genes in Vitis.
2􀆰 5  Conserved domains and motifs in UBX proteins
The major domains of the UBX proteins in Po ̄
pulusꎬ Vitis and Arabidopsis were verified using Pfam
and SMART (Punta et al.ꎬ 2012ꎻ Letunic et al.ꎬ
2012). While these tools are unable to recognize
smaller or more divergent motifsꎬ we used MEME to
discern for more detailed motif informationꎬ and thir ̄
ty distinct motifs were identified in these proteins
(right panel in Fig􀆰 1). Our result shows that seven
groups have different types of motif compositionꎻ
these motifs are highly conserved in the same groupꎬ
suggesting closely evolutionary relationships and sim ̄
ilar function among group members.
Most UBX members in all the seven subgroup
shared motif 1 (Fig􀆰 1)ꎬ suggesting its conservative
and functional importance. So we illustrated the top
one conserved motif ( motif 1) with sequence logo
(Fig􀆰 4). From the sequence logoꎬ we can determine
the consensus sequence and the relative frequency of
bases and the information content ( measured in
bits) at every position in a site (Schneider and Ste ̄
phensꎬ 1990). The logo displays both significant
residues and subtle sequence patterns.
Fig􀆰 4  Sequence logo plot of the top one conserved motif (motif 1) identified by MEME program for all the predicted full ̄length UBX proteins.
The height of a letter indicates its relative frequency at the given position (x ̄axis) in the motif. Numbers on the x ̄axis represent the sequence
positions in zinc finger motifs. The sequence logos were derived using WebLogo (Crooks et al.ꎬ 2004)
3  Conclusion
This study provides a comparative genome anal ̄
ysis including phylogenyꎬ chromosomal locationꎬ
gene structure of the UBX family in Populus and Vi ̄
tis. The exon / intron gene structure and motif compo ̄
sition were relatively conserved in the same group.
Duplication analyses suggested tandem duplication
and segmental duplication contribute to the expan ̄
sion of Populus and Vitis UBX gene familyꎬ while
some gene loss has also occurred. The results pres ̄
ented in this study provide basic information on UBX
proteinsꎬ which may provide valuable information for
future functional investigations of this family.
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