全 文 ：作物学报 ACTA AGRONOMICA SINICA 2009, 35(12): 2218−2224 http://www.chinacrops.org/zwxb/
ISSN 0496-3490; CODEN TSHPA9 E-mail: xbzw@chinajournal.net.cn

This study was supported by Natural Science Foundation of Fujian Province (2006J0059), National Natural Science Foundation of China (30900915),
and the foundation for young scholars in Fujian Agriculture and Forestry University (08B12).
* Correspondence author: PAN Da-Ren, E-mail: pandaren@yahoo.com.cn; Tel: +86 59183798876
Received(收稿日期): 2008-12-31; Accepted(接受日期): 2009-06-25.
DOI: 10.3724/SP.J.1006.2009.02218
Isolation and Characterization of IbNPR1 Gene from Sweet Potato (Ipo-
moea batatas)
CHEN Guan-Shui1, ZHOU Yi-Fei2, LIN Sheng1, ZHANG Zheng1, and PAN Da-Ren1,*
1College of Life Science, Fujian Agriculture and Forestry University, Fuzhou 350002, China; 2College of Crop Science, Fujian Agriculture and
Forestry University, Fuzhou 350002, China
Abstract: NPR1 (non-expressor of pathogenesis-related genes 1) protein is a key regulator of salicylic acid (SA)-mediated gene
epression in systemic acquired resistance (SAR). By using homologous cloning and RACE (rapid amplification of cDNA ends)
techniques, a full-length cDNA of IbNPR1 (Ipomoea batatas non-expressor of pathogenesis-related genes 1) was isolated from
sweet potato var. Qingnong 2. The full length cDNA was 2 353 bp, including an ORF (open reading frame) putatively encoding a
polypeptide of 586 amino acids residues with a predicted molecular mass of 64.851 kD. The deduced amino acid sequence shared
structural features with known NPR1 (-like) proteins: ankyrin repeat and BTB/POZ. Furthermore, phylogenetic analysis showed
IbNPR1 had the closest association with LeNPR1 from Lycopersicon esculentum. Southern-blot analysis revealed that the IbNPR1
belonged to low-copy gene family in sweet potato. Semi-quantitative RT-PCR analysis indicated that IbNPR1 was constitutively
expressed in roots, stems and leaves. In addition, IbNPR1 could be induced by salicylic acid. The results suggest that IbNPR1
plays an important role in the response to pathogen infections in sweet potato.
Keywords: Ipomoea batatas; IbNPR1 gene; Disease resistance; RACE
甘薯 IbNPR1全长 cDNA序列的分离与表达特性分析
陈观水 1 周以飞 2 林 生 1 张 铮 1 潘大仁 1,*
1 福建农林大学生命科学学院, 福建福州 350002; 2 福建农林大学作物科学学院, 福建福州 350002
摘 要: 在植物系统获得性抗性(SAR)中, NPR1 蛋白是水杨酸介导的基因表达中关键调控因子。本研究以青农 2 号
为试验材料, 利用同源序列法和 RACE技术分离甘薯 SAR 途径的主要抗病信号元件 NPR1 (none expresser of PR gene)
的全长 cDNA序列。序列分析表明, IbNPR1基因全长 2 353 bp, 包含一个编码 586个氨基酸残基的开放阅读框, 包含
有类似拟南芥 NPR1 蛋白中的 BTB/POZ 和锚蛋白重复氨基酸序列结构域。聚类分析显示 IbNPR1 与来源于番茄的
NPR1 蛋白关系最近。Southern 杂交及半定量 RT-PCR 分析表明, 甘薯 NPR1 基因属于低拷贝基因家族, 表达模式为
组成型表达, 并且 SA能提高其表达水平。由该结果推测, IbNPR1可能在甘薯抵御病原物的侵染中起重要的作用。
关键词: 甘薯; IbNPR1基因; 抗病; cDNA末端快速扩增技术
Plants have many signal transduction pathways
against pathogen attack. The defense response generated
by the induction of these pathways can be either specific
against a particular pathogen, as is the case for resistance
(R)-gene-mediated resistance, or general against a broad
spectrum of pathogens. Systemic acquired resistance
(SAR) is a long-lasting plant defense response that con-
fers broad spectrum resistance to viral, bacterial, and
fungal pathogens and induces expression of pathogene-
sis-related (PR) genes [1]. The previous reports showed
that small molecules including salicylic acid (SA), jas-
monic acid (JA) and ethylene (ET) acted as secondary
messengers to mediate and regulate signaling networks in
plant defense response. SA was required for the estab-
lishment of SAR defense response. The application of
exogenous SA, or SA analogs, such as 2,6-dichloroi-
sonicotinic acid (INA) and benzo (1,2,3) thiadiazole-7-
carbothioic acid S-methylester (BTH) could also raise the
activation of SAR[2-5]. The efforts to genetically elucidate
the SAR pathway downstream of the SA signal have al-
ways been linked to the discovery of numerous alleles of
a single gene designated NPR1 (nonexpressor of PR1
genes, also known as NIM1 and SAI1). In Arabidopsis
thaliana, NPR1 has been identified as a positive regula-
第 12期 陈观水等: 甘薯 IbNPR1全长 cDNA序列的分离与表达特性分析 2219


tory protein of the SA-regulated PR gene expression and
disease resistance. Npr1 mutants not only fail to express
PR-1, PR-2, and PR-5 but also display enhanced suscep-
tibility to pathogen even after treatment with SA or INA
[6-7]. Recent researches have shown that NPR1 is essential
in balancing SA- and JA/ET-dependent signal transduc-
tion pathways as a cross-talk point through either direct
or indirect interaction with some WRKY transcription
factors (TFs) in Arabidopsis thaliana [3,5,8-9]. Together, the
data indicated that NPR1 is a key node of the plant dis-
ease-resistance signal network. NPR1 plays a pivotal role
in systemic acquired resistance (SAR) and induced sys-
temic resistance (ISR), and also in basic resistance and
resistance (R) gene-dependent resistance [5]. Overexpres-
sion of NPR1 results in enhanced resistance against
various pathogens in transgenic plants, such as Arabi-
dopsis thaliana, rice (Oryza sativa), tobacco (Nicotiana
benthamiana), and tomato (Lycopersicon esculentum)
[9-14]. NPR1 encodes a protein containing a bipartite nu-
clear localization sequence (NLS) and two conserved
protein-protein interaction domains: a BTB/POZ (broad-
complex, tramtrack and bric-abrac/pox virus and zinc
finger) and an ankyrin repeat domain (ARD). Nuclear
localization of NPR1 protein is essential for its biological
function [1,5,16-18]. In the absence of SAR induction, NPR1
protein forms an oligomer through intermolecular disul-
fide bonds and is excluded from the nucleus. However, in
the presence of SAR induction, plant cells attain a more
reduced environment due to the accumulation of antioxi-
dants [7,19], and under these conditions, NPR1 protein
transitions from an oligomeric to a monomeric form by
reducing two of its cysteines. The monomeric and re-
duced form of NPR1 is then translocated from the cyto-
sol to the nucleus where it can control PR gene expres-
sion. NPR1 redox modification and subsequent translo-
cation to the nucleus are both necessary for SAR.
Sweet potato [Ipomoea batatas (L.) Lam.] is a mem-
ber of the family Convolvulaceae, Genus Ipomoea, sec-
tion batatas. It is the only hexaploid (2n=6x=90) in this
section. Sweet potato is widely used as food and animal
feed and is often processed into starch, liquor, and a vari-
ety of other industrial products. However, its yield is
strongly affected by various diseases caused by fungi,
nematode, virus, etc. [20] To our knowledge, relatively
little is known about NPR1 proteins of sweet potato, and
no data are available on NPR1 gene family, gene struc-
ture and expression characterization in sweet potato. In
this study, we isolated and characterized NPR1 homo-
logue from sweet potato, designated as IbNPR1 (Ipomoea
batatas NPR1). The results will help to understand
NPR1-mediated resistance and a practical strategy for the
improvement of disease resistance in sweet potato.
1 Materials and Methods
1.1 Materials and treatment
A sweet potato cultivar Qingnong 2 (highly resistant
to knot nematode) was grown in a test field in Fujian
Agricultural and Forestry University. SA was sprayed on
sweet potato leaves at concentration of 1 mmol L−1. The
leaf tissues were sampled at time points of 0, 4, 8, 12, 24,
and 48 h after spraying. Total RNAs were extracted from
the treated leaves.
The Escherichia coli strain DH5α is from our labora-
tory. The RNAiso Reagent Kit, PCR fragment Recovery
Kit, PCR cloning vector pMD-18T, restriction enzymes
and rest tool enzymes were purchased from TaKaRa
Biotechnology Company (Dalian, China), BD SMARTTM
RACE cDNA Amplification Kit from BD Bioscience
Clontech Company, M-MLV transcriptase from Gibco
BRL Company. All other chemical reagents were ana-
lytical purity.
1.2 Isolation of Total RNA and DNA
Total RNA was isolated with RNAiso Reagent (Ta-
KaRa, Dalian, China) according to the instructions. Ge-
nomic DNA was extracted from young leaflets using
CTAB method, as described by Guo et al. [21]
1.3 Cloning of IbNPR1 internal fragment and
RACE
cDNA synthesis was performed using M-MLV tran-
scriptase (Gibco BRL, Cleveland, USA) according to the
manufacturers’ manuals. On the basis of the conserved
amino acid and nucleotide sequences of other known
NPR1, the forward primer IbNPRF1 and reverse primer
IbNPRR1 (Table 1) used for cloning of internal conser-
vative cDNA fragment were designed and synthesized.
RT-PCR condition was as follows: 94℃ for 5 min, fol-
lowed by 35 cycles of 94℃ for 45 s, 59℃ for 50 s, 72
℃ for 90 s, and 72℃ for 10 min. The PCR products
were purified and ligated with pMD-18T vector (TaKaRa,
Dalian, China). Recombinant clones were sequenced
twice using an ABI377 automated sequencer (Sangon,
Shanghai, China).
RACE was performed according to the manual of the
BD SMARTTM RACE cDNA amplification Kit (Clontech,
Palo Alto, California, USA). Based on the internal cDNA
fragment of IbNPR1, a gene-specific primer (IbNPR-
GSP5) for 5RACE was designed (Table 1). The 5′ cDNA
ends were amplified using BD SMARTTM RACE cDNA
Amplification Kit following the User Manual (Clontech,
Palo Alto, California, USA). The PCR products were
cloned into the pMD-18T vector and sequenced. Based
on the sequence of 5RACE product, another
gene-specific primer (IbNPRGSP3) was designed for
3′RACE (Table 1).
1.4 Cloning the full-length cDNA of IbNPR1
The alignment analysis of 5′RACE and 3′RACE
product sequences from cDNA internal fragment was
performed with DNAMAN software (version 6.0) pack-
age (http://www.lynnon.com/). The full-length cDNA of
IbNPR1 was obtained through RT-PCR amplification
using primers FIbNPRF and FIbNPRR (Table 1).

2220 作 物 学 报 第 35卷

Table 1 Primers used for the cloning of IbNPR1 in amplification
Name Sequence (5′→3′) Description
IbNPRF1 ATTGTCAARTCTRAYGTDGAT Degenerate primer, forward
IbNPRR1 AACTCTGTTTTCAAGGT Degenerate primer, reverse
IbNPRF2 ATTGTCAAATCAGATGTTGAT IbNPR1 specific primer, forward
IbNPRR2 TTCATCGCAGATCATCACC IbNPR1 specific primer, reverse
ACTINF TCCGTGACATCAAGGAAAAG Inner control primer, forward
ACTINR GATATCAACATCGCACTTCATG Inner control primer, reverse
IbNPRGSP5 TAATGCCTCACCCTTTACCACACG 5′RACE reverse primer
IbNPRGSP3 GCGGTTGTGTTTAGAGATTCTGGAGC 3′RACE forward primer
FIbNPRF CTGTATAATGGATGTAAGAATGGGG Full-length cDNA and DNA primer, forward
FIbNPRR GTACAACATAGAAATTCACCATAGGG Full-length cDNA and DNA primer, reverse


The PCR products were cloned into the pMD-18T
vector and sequenced. The full-length cDNA sequence of
IbNPR1 was then analyzed for molecular characteriza-
tion.
1.5 Sequence analysis
Nucleotide sequence analysis and translation into the
corresponding amino acid sequence were performed us-
ing DNAMAN (ver. 6.0) software. Similarity searches
were performed with Blastx and Blastp program in the
NCBI (National Centre for Biotechnology Information)
website. Multiple alignments were performed with
ClustalW1.8 software and DNAMAN software (ver. 6.0)
package. Phylogenetic and molecular evolutionary analy-
sis were conducted using MEGA software (ver. 3.1). The
Bootstrap value was used to evaluate the reliability.
1.6 Southern blot analysis
30 µg genomic DNA was digested with Sac I and Kpn
I. The digested DNA were fractionated on 1.0% (M/V)
agarose gels, and then transferred onto a positively
charged Hybond-N+ nylon membranes (Amersham,
Germany) according to the manufacturer’s instruction.
The membrane was subsequently hybridized with a ran-
domly-labeled IbNPR1 fragment generated with specific
primers IbNPRF2 and IbNPRR2. Southern blot was per-
formed according to the manufacturer’s instructions. Hy-
bridization of DNA transferred to nylon membranes was
performed using a nonradioactive digoxigenin-probe
labelling system (PCR DIG Probe kit, Roche Diagnos-
tics).
1.7 Expression analysis of IbNPR1 in sweet potato
Semi-quantitative RT-PCR was used to investigate
IbNPR1 expression profiling in various tissues of sweet
potato and in response to SA. Amplification for IbNPR1
was performed at 94oC for 5 min followed by 28 cycles
of amplification (94oC for 45 s, 58oC for 50 s, 72oC for
90 s) using primers IbNPRF2 and IbNPRR2 (Table 1),
which amplified a fragment of 780 bp. At the same time,
sweet potato β-actin gene was used as the internal control
with primers ACTINF and ACTINR (Table 1).
2 Results
2.1 Cloning and sequence analysis of IbNPR1
cDNA
On the basis of the conserved region of NPR1 proteins
cloned from other plants, a fragment of about 600 bp was
amplified with primers IbNPRF1 and IbNPRR1 (Fig.
1-A). Specific primers (IbNPRGSP3 and IbNPRGSP5)
were subsequently used for the amplification of 3′-end
and 5′-end cDNA, resulting in fragments of approxi-
mately 1 400 bp (Fig. 1-B) and 1 000 bp (Fig. 1-C) at the
3′-end and the 5′-end, respectively. By comparing and
aligning the sequences of 3′RACE and 5′RACE products,
the full-length cDNA of Ipomoea batatas NPR1 (desig-
nated as IbNPR1, GenBank accession No. EF190039)
was obtained. The full-length cDNA of IbNPR1 com-
prised 2 353 bp including the 5′-untranslated region,
coding sequence, 3′-untranslated region and poly (A) tail.
The longest open reading frame started at nucleotide 163
and ended at nucleotide 1 938, encoding a putative 586
amino acids polypeptide with calculated molecular
weight (MW) of 64.851 kD and an isoelectric point (pI)
of 6.06.


Fig. 1 RACE results of IbNPR1 cDNA
A: PCR products amplified by primes IbNPRF1 and IbNPRR1;
B: 3′RACE products; C: 5′RACE products.
第 12期 陈观水等: 甘薯 IbNPR1全长 cDNA序列的分离与表达特性分析 2221


Bioinformatics analysis indicated that the IbNPR1
gene contains an ankyrin repeat domained (from 259 to
391 residues) and a BTB/POZ domain (from 65 to 138
residues). Both of the domains were highly conserved
among all NPR1 proteins and involved in protein–protein
interactions (Fig. 2). Multiple alignment analysis showed
amino acids which are crucial for the NPR1 function as
defined by genetic mutants, such as npr1-1(H), npr1-2(C),
and nim1-4(R), are conserved in deduced amino acid of
IbNPR1 (Fig. 2). In addition, a potential bipartite NLS
(nuclear localization sequence) was found in the
C-terminal 55 amino acids of IbNPR1 (designated as A
and B), which were rich in basic residues (Fig. 2). NLSs
have been shown to be required for nuclear import of
NPR1 or NPR1-like proteins in both plants and animals.
Blast results indicated that the deduced amino acid
sequence of IbNPR1 was highly similar to CaNPR1 from
Capsicum annuum (80% identity, 88% positivity),
NtNPR1 from Nicotiana tabacum (79% identity, 88%
positivity), LeNPR1 from Lycopersicon esculentum (79%
identity, 88% positivity), GhNPR1 from Gossypium hir-
sutum (66% identity, 81% positivity), OsNPR1 from
Oryza sativa (57% identity, 74% positivity), AtNPR1
from Arabidopsis thaliana (52% identity, 70% positivity)
and BjNPR1 from Brassica juncea (50% identity, 69%
positivity).



Fig. 2 Multiple alignment of the amino acid sequences of deduced IbNPR1 protein with related NPR1 proteins
The alignment was performed with ClustalW1.8 software and DNAMAN software (version 6.0) package using the published amino-acid sequences of
IbNPR1 (EF190039), BjNPR1 (DQ359129), CaNPR1(DQ648785), AtNPR1(EF470718), NtNPR1(DQ837218), LeNPR1(AY640378),
GhNPR1(DQ325523), and OsNPR1(AK067198). Comparison of IbNPR1 and related NPR1 proteins indicated that there were two functional domains:
the BTB domain (I) and the ankyrin repeat sequence (II). Seven conserved cysteine residues are indicated by asterisks; these residues may control the
oligomerization state. Three crucial amino acids for NPR1 function, such as npr1-1(H), nprl-2(C), niml-4(R), were indicated (↓). Two potential NLSs
which are used for the nuclear localization are designated by A and B.
2222 作 物 学 报 第 35卷

2.2 Molecular evolution analysis
Phylogenetic analysis was performed to characterize
the evolutionary relationships among different NPR1
proteins from various plant species using the Clustal
W1.8 and MEGA 3.0 programs. In the phylogenetic tree
(Fig. 3), the 8 members of plant NPR1 proteins were di-
vided into two major groups. Among these NPR1 pro-
teins, IbNPR1 was most closely related to LeNPR1 from
Lycopersicon esculentum.



Fig. 3 Neighbor-joining phylogenetic tree for NPR1 proteins from
different species
The phylogenetic tree was generated using the MEGA3.0 software. All
the amino acid sequences of NPR1 and NPR1-like proteins used for
construction of the tree were derived from the GenBank database under
the following accession numbers: AtNPR1 (EF470718) from Arabidop-
sis thaliana; BjNPR1(DQ359129) from Brassica juncea; CaNPR1
(DQ648785) from Capsicum annuum; GhNPR1(DQ325523) from
Gossypium hirsutum; NtNPR1 (DQ837218) from Nicotiana tabacum;
LeNPR1(AY640378) from Lycopersicon esculentum; OsNPR1
(AK067198) from Oryza sativa; IbNPR1 (EF190039) from Ipomoea
batatas. The numbers on the branches indicate bootstrap values (1 000
iterations).

2.3 Southern blot analysis
To investigate the genomic organization of IbNPR1
gene in sweet potato, genomic DNA was digested with
Sac I and Kpn I, and hybridized with IbNPR1 cDNA
fragment. As shown in Fig. 4, one band was detected for
Sac I digestion, and two bands were detected for Kpn I
digestion. The results suggested that IbNPR1 belongs to a
low-copy gene family.


Fig. 4 Southern blot pattern of the IbNPR1 gene
Genomic DNA isolated from leaves of sweet potato was digested with
Sac I (lane S) and Kpn I (lane K), respectively, followed by hybridiza-
tion with IbNPR1 coding sequence as the probe.
2.4 Expression pattern of IbNPR1 gene in differ-
ent tissues
To determine the tissue-specific expression pattern
of the IbNPR1 gene, semi-quantitative RT-PCR was
performed using total RNA extracted from roots, stems
and leaves. As shown in Fig. 5, the IbNPR1 gene ex-
pression was observed in root, stem, and leaf. The ex-
pression level had no significant difference in different
tissues.



Fig. 5 Expression profiling of IbNPR1 gene in different tissues by
semi-quantitative RT-PCR
R: root; S: stem; L: leaf. Twenty-eight cycles were used for the PCR
amplification of IbNPR1 and β-actin (as the control).

2.5 Expression of IbNPR1 in response to SA
The NPR1 transcript level was increased with treat-
ment of SA or SA analogs and pathogen infection which
resulted in the activation of SAR. The gene expression
patterns of IbNPR1 in response to SA showed that
IbNPR1 mRNA accumulated rapidly and stably com-
pared with the unstressed control samples. It suggested
that IbNPR1 is constitutively expressed at low levels but
is induced by exogenous application of SA.
3 Discussion
NPR1 is a key regulator of SAR-related PR gene ex-
pression, which confers lasting broad-spectrum resistance.
Since 1997, many NPR1 homologs have been isolated
from Arabidopsis thaliana, Capsicum annuum, Nicotiana
tabacum, Lycopersicon esculentum, Gossypium hirsutum,
Beta vulgaris, Carica papaya, Brassica juncea and
Oryza sativa [6,10,13,22-23]. Presently, the molecular and
biochemical characterization of both NPR1 and analo-
gous genes are extensively studied in model plant species,
such as Arabidopsis, tobacco, cotton and rice. However,
neither NPR1 nor its analogues in sweet potato (Ipomoea
batatas) have been reported.
In this report, the full-length cDNA of NPR1 gene was
first isolated from sweet potato, which provides an evi-
dence of the presence of a NPR1 homolog in sweet po-
tato. The derived amino acid sequence of IbNPR1 cDNA
shows 80% identity to CaNPR1, 79% identity to NtNPR1,
66% identity to GhNPR1, 70% identity to CpNPR1, 57%
identity to OsNPR1, and 52% identity to AtNPR1. Addi-
tionally, it bears all the important functional domained,
such as the ankyrin repeats and the BTB-POZ domains,
第 12期 陈观水等: 甘薯 IbNPR1全长 cDNA序列的分离与表达特性分析 2223


presented in other plant NPR1 protein (Fig. 2). Previous
reports indicated that two conserved cysteine residues
(Cys82 and Cys216) were essential for the formation of
the AtNPR1 oligomer through disulfide bonds, and that
mutations in these residues cause constitutive mono-
merization and localization of AtNPR1 to the nucleus[1,23].
In rice, two conserved cysteine residues (Cys76 and
Cys216) play an essential role in OsNPR1 oligomer for-
mation [15]. Sequence alignment analysis indicated that
the IbNPR1 protein also contains two conserved cysteine
residues at positions 81 and 214 (Fig. 2). In addition, the
positions of single-point mutations, such as npr1-1(H),
npr1-2(C), and nim1-4(R), could also cause loss of func-
tion of NPR1 in Arabidopsis thaliana. Multiple align-
ment analysis showed three crucial amino acids for
NPR1 function, such as npr1-1(H), nprl-2(C), niml-4(R),
are conserved in IbNRP1 protein (Fig. 2). The mutation
analysis of these residues is currently in progress to ver-
ify their function in IbNPR1.
In Arabidopsis thaliana, NPR1 has been identified as
a positive regulatory protein of the SA-regulated PR gene
and disease resistance. The studies indicated that NPR1
was essential in balancing SA- and JA/ET-dependent
signal transduction pathways as a cross-talk point of a
variety of defensive signal pathways [3,9]. Previous reports
showed that NPR1 had different genome organization
patterns in different plant species. For example, there
were at least six and five NPR1-like genes in the Arabi-
dopsis thaliana genome and in the rice genome, respec-
tively[9,13,15]. However, NPR1 is a single copy in the Gos-
sypium hirsutum and Thinopyrum intermedium ge-
nomes[23-24]. In this study, the result showed that IbNPR1
presented with a low copy in the sweet potato genome. A
weaker band detected by Southern blot analysis may
represent other NPR1-like genes in the sweet potato ge-
nome (Fig. 4). However, the number of NPR1-like genes
in sweet potato and the analysis of their functions remain
to investigate in the future.
The NPR1 was found to constitutively express in un-
treated plants and to be induced moderately by the appli-
cation of exogenous SA, or SA analogs [6,15,22-26]. In this
study, like the NPR1 in Arabidopsis thaliana, the IbNPR1
was transcribed in different tissues and enhanced by the
application of exogenous SA (Fig. 5 and Fig. 6). We also
found that IbNPR1 was highly homologous to NtNPR1,
LeNPR1 and CpNPR1. Therefore, we predicted that
IbNPR1 contributes to the positive regulation of SAR on
biotic stress defense.
It is the first study to reveal the existence of NPR1 in
sweet potato and its expression pattern upon chemical
treatment. Isolation and characterization of NPR1 gene
from sweet potato pave a way for research on NPR1-
based resistance against fungal and bacterial diseases in
sweet potato. Further functional analysis of IbNPR1 is
now under intensive investigation in our laboratory.



Fig. 6 Expression profiling of IbNPR1 gene in response to salicylic
acid (SA)
RNA from the treated (1.0 mmol L−1 SA) leaves of sweet potato was
subjected to semi-quantitative RT-PCR. Numbers indicate the time
intervals after treatment with SA.

4 Conclusion
The full length cDNA encoding a sweet potato NPR1
protein, designated IbNPR1, was isolated by RT-PCR and
RACE methods (GenBank accession No. EF190039).
The putative IbNPR1 protein, with a molecular weight
(MW) of 64.851 kD and an isoelectric point (pI) of 6.06,
has two conservative function domains (an ankyrin re-
peat domain and a BTB/POZ domain) of the known
NPR1 protein. In addition, the IbNPR1 belonged to low
copy family, was transcribed in different tissues and en-
hanced by the application of exogenous SA. The results
suggest that IbNPR1 is potentially involved in signalling
defence responses.
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