全 文 :植物科学学报 2014ꎬ 32(4): 394~405
Plant Science Journal
DOI: 10 3724 / SP J 1142 2014 40394
冬性植物红菜薹在不同温度处理下花青素积累的分子机制
魏国超ꎬ 程 钧ꎬ 马百全ꎬ 王 鲁ꎬ 谷 超ꎬ 韩月澎∗
(中国科学院武汉植物园ꎬ 中国科学院植物种质创新与特色农业重点实验室ꎬ 武汉 430074)
摘 要: 芸薹属植物红菜薹(Brassica rapa)是一种常见的蔬菜ꎬ 它的花茎和叶柄表皮中均积累有花青素ꎮ 为了
解红菜薹中花青素合成的分子机制ꎬ 进行了花青素含量的测定和花青素合成相关基因的表达分析ꎮ 研究结果表
明ꎬ 叶柄表皮中的花青素含量显著高于叶片(去主脉)的花青素含量ꎮ 同时ꎬ 叶柄表皮花青素合成相关基因的表
达水平高于叶柄(去表皮)和叶片(去主脉)的表达水平ꎬ 这表明红菜薹中花青素的合成调控发生在转录水平ꎮ
BrMYBA1仅在叶柄表皮中表达ꎬ 但 BrbHLH1 和 BrWD40 在叶片和叶柄表皮中均能检测到表达ꎮ 因此ꎬ BrMY ̄
BA1的转录激活可能与红菜薹的花青素合成相关ꎮ 连续低温处理时ꎬ 红菜薹叶柄表皮中的花青素含量逐渐增加ꎬ
而该组织中花青素合成的结构基因表达水平逐渐降低ꎮ
关键词: 红菜薹ꎻ 花青素ꎻ BrMYBAꎻ 转录因子
中图分类号: Q945ꎻ S634 703 文献标识码: A 文章编号: 2095 ̄0837(2014)04 ̄0394 ̄12
收稿日期: 2014 ̄03 ̄17ꎬ 退修日期: 2014 ̄03 ̄27ꎮ
基金项目: 国家自然科学基金项目(National Natural Science Foundation of Chinaꎬ No. 31000139)ꎮ
作者简介: 魏国超(1988-)ꎬ 男ꎬ 硕士研究生ꎬ 研究方向为园林与观赏植物遗传与育种(E ̄mail: weiguochaohn@126. com)ꎮ
∗通讯作者(Author for correspondence E ̄mail: yphan@wbgcas. cn)ꎮ
Molecular Characterization of Anthocyanin Accumulation
under Different Temperatures in Winter Plant
Hongcaitai (Brassica rapa L.)
WEI Guo ̄Chaoꎬ CHENG Junꎬ MA Bai ̄Quanꎬ WANG Luꎬ GU Chaoꎬ HAN Yue ̄Peng∗
(Key Laboratory of Plant Germplasm Enhancement and Specialty Agricultureꎬ Wuhan
Botanical Gardenꎬ Chinese Academy of Sciencesꎬ Wuhanꎬ 430074ꎬ China)
Abstract: Hongcaitai (Brassica rapa) is a vegetable that accumulates anthocyanins in both
floral stems and leaf petioles. To understand the mechanism underlying the regulation of
anthocyanin biosynthesis in B. rapaꎬ anthocyanin accumulation and expression patterns of
anthocyanin biosynthesis genes in seedlings of Hongcaitai were investigated. Anthocyanin
content in epidermal tissues of petioles were significantly higher than those in leaves with
excised mid ̄veins. Expression levels of all anthocyanin biosynthesis pathway genes were
significantly higher in epidermal tissues of petioles than those detected in either endodermal
tissues of petioles or in leavesꎬ suggesting that anthocyanin biosynthesis was regulated at the
transcriptional level. Transcripts of BrMYBA1 were exclusively expressed in the petiole
epidermisꎻ whereasꎬ transcripts of BrbHLH1 and BrWD40 were detected in both leaves and
petiole epidermal tissues. This suggests that activation of BrMYBA1 was likely responsible for
anthocyanin pigmentation in Hongcaitai. Following cold treatmentꎬ seedlings demonstrated
increased accumulation of anthocyanins in petiole epidermal tissuesꎬ while the transcription of
anthocyanin pathway genes was reduced in petiole epidermal tissues.
Key words: Brassica rapaꎻ Anthocyaninꎻ BrMYBAꎻ Transcription factors
Hongcaitai (Brassica rapa L. ssp. chinensis
L. var. purpurea Bailey)ꎬ one of the most popular
Chinese vegetables and a specialty crop in Wu ̄
hanꎬ Chinaꎬ produces anthocyanin pigments in
its floral stems and leaf petioles. Brassica rapa
(syn. B. campestris) is a diploid with 2n = 20.
Anthocyanins are not only responsible for red
coloration in various plant speciesꎬ but they also
provide benefits for human health due to their an ̄
tioxidant activities[1] . Despite the functional value
of anthocyanin pigmentsꎬ howeverꎬ few studies
have been reported on the mechanism regulating
anthocyanin biosynthesis in B. rapa. The antho ̄
cyanin biosynthetic pathway is the most well ̄
known secondary metabolite pathway in plants[2] .
The synthesis of anthocyanins is complex and in ̄
volves coordinated activities of different classes
of enzymesꎬ including chalcone synthase
(CHS)ꎬ chalcone isomerase (CHI)ꎬ flavanone
3 ̄hydroxylase ( F3H)ꎬ flavanone ̄3′ ̄hydroxylase
(F3′H)ꎬ flavanone 3′5′ ̄hydroxylase (F3′5′H)ꎬ
dihydroflavonol 4 ̄reductase (DFR)ꎬ leucoanthoc ̄
yanidin dioxygenase (LDOX)ꎬ flavonol synthase
( FLS )ꎬ and UDP ̄glucose: flavonoid 3 ̄O ̄glu ̄
cosyltransferase (UFGT) . Several genes involved
in anthocyanin biosynthesis have been isolated
and functionally characterized in many plants.
These can be divided into two classesꎬ structural
genes encoding anthocyanin pathway enzymes
and regulatory elements[3] . The regulatory ele ̄
ments consist of three groups of transcription fac ̄
tors (TFs)ꎬ including MYBꎬ basic helix ̄loop ̄helix
(bHLH)ꎬ and WD40. The structural genes are
regulated at the transcriptional level by combina ̄
torial actions of MYBꎬ bHLHꎬ and WD40 TFs.
Thereforeꎬ anthocyanin pigmentation is primarily
controlled by regulatory genes[4] .
Besides internal genetic factorsꎬ external en ̄
vironmental factors such as temperatureꎬ lightꎬ
and nutrition also influence anthocyanin biosyn ̄
thesis[5-7] . Among these environmental factorsꎬ
temperature exerts a major influence on anthoc ̄
yanin accumulation in a wide variety of plants. For
exampleꎬ high temperature reduces anthocyanin
concentrationꎬ resulting in reduced red color in ̄
tensity of fruit skin of grapes and apples[8ꎬ9] . Two
mechanisms have been proposed for the ob ̄
served lower anthocyanin levels in plants ex ̄
posed to high temperatureꎻ specificallyꎬ high
temperature inhibits transcription of anthocyanin
biosynthetic genesꎬ leading to a reduced rate of
anthocyanin synthesis[7ꎬ10ꎬ11]ꎬ and high tempera ̄
ture results in both reduced synthesis and in ̄
creased degradation of anthocyanins[12] . In con ̄
trastꎬ low temperature can induce the expression
of anthocyanin biosynthetic genesꎬ resulting in in ̄
creased anthocyanin pigmentation in plants such
as maize[13]ꎬ Arabidopsis[14]ꎬ petunia[15]ꎬ red
orange[16]ꎬ grape[11]ꎬ and apple[17] . Howeverꎬ
few studies have been reported on anthocyanin
pigmentation in annual plants that germinate in
fall or winterꎬ survive the winterꎬ and then bloom
in late winter or spring.
Hongcaitai is a winter annual vegetableꎬ and
its leavesꎬ flower budsꎬ and stems are all edible.
Its commercial importance is highly related to an ̄
thocyanin pigmentation in flower stems and pe ̄
tioles. The red coloration of flower stems and pe ̄
tioles increases as temperature dropsꎬ and shows
high pigmentation following the first frost. To
understand the mechanisms that underlie anthoc ̄
yanin pigmentation and its response to low tem ̄
perature in B. rapaꎬ we investigated anthocyanin
accumulation and expression of anthocyanin
biosynthesis genes in petioles of Hongcaitai grown
under low temperature. Our results revealed that
BrMYBA1 plays an important role in regulation of
anthocyanin accumulationꎬ and that expression
levels of anthocyanin structural genes decrease
at cold temperatures. These findings have impli ̄
593 第 4期 魏国超等: 冬性植物红菜薹在不同温度处理下花青素积累的分子机制(英文)
cations for the management of B. rapa vegeta ̄
bles and selection of cultivars with enhanced red
coloration during cold winter weather.
1 Materials and Methods
1 1 Materials
Two subspecies of B. rapaꎬ Hongcaitai and
Chinese cabbage (Brassica campestris L. ssp.
pekinensis ( Lour.) Makino)ꎬ were used in the
study. Hongcaitai produces purple ̄colored stems
and petioles with green and / or white ̄colored
flesh along with green ̄colored leavesꎬ but with
red mid ̄veinsꎬ while Chinese cabbage accumu ̄
lates no anthocyanins and has green leaves and
white petioles (Fig 1) .
Seeds were sown on 20 Augustꎬ 2012ꎬ and
seedlings were transplanted into small pots on 28
Septemberꎬ 2012. Each pot contained a single
seedling. All seedlings were grown outdoors for a
period of one month at Wuhan Botanical Garden
(Chinese Academy of Sciencesꎬ Hubeiꎬ China) .
Seedlings were then transferred to a growth
chamber and grown under three consecutive en ̄
vironmental conditions: 20℃ and 60% relative
humidity (RH) for 7 dꎬ 10℃ and 60% RH for
7 dꎬ and 2℃ and 60% RH for 7 d. Leaves and
petioles were collectedꎬ with three biological
replicatesꎬ after 7 days of growth at each of the
temperature treatments. Subsequentlyꎬ mid ̄rib
veins were excised from the leavesꎬ and epider ̄
mal and endodermal tissues of petioles were se ̄
parated. All tissues were immediately frozen in
liquid nitrogenꎬ and stored at -75℃ until use.
1 2 Methods
1 2 1 Extraction and determination of total an ̄
thocyanins in leaves and petiolar tissues
Anthocyanin content was assayed as pre ̄
viously described by Niu et al. (2010) [18] . Brief ̄
lyꎬ 01 g of sample was ground into powder in li ̄
quid nitrogenꎬ then added to 1 mL of extraction
solution (0 1% HCl in methanol)ꎬ and incubated
at 4℃ for 20 h. The mixture was centrifuged at
12 000 r / min for 20 minꎬ and the supernatant
was transferred to a clean tube. The pellet was
dissolved in 1 mL of extraction solutionꎬ and the
mixture was extracted again. The supernatants
were combined and diluted in 3 mL of extraction
solution. Thenꎬ 200 μL of supernatant was mixed
A: Seedling of Hongcaitaiꎻ B: Flower stem of Hongcaitaiꎻ C: Petiole of Hongcaitaiꎻ D: Seedling of Chi ̄
nese cabbageꎻ E: Petiole of Chinese cabbageꎻ F: Petiole endodermis of Chinese cabbage.
Fig 1 Diagram of coloration in B. rapa
693 植 物 科 学 学 报 第 32卷
with 3 mL of either buffer A (0 05 mol / L KCl and
0 15 mol / L HClꎬ pH 1 0) or buffer B (0 2 mol / L
NaAc with pH 4 5) and stored at 4℃ for 2 h. The
absorbance of buffer A and B was measured at
520 and 700 nmꎬ respectively. The anthocyanin
content was calculated according to the following
formula[19]: TA = [(A × MW × DF × V) / (ε × L ×
Wt)] × 100ꎬ where TA stands for total anthocya ̄
nin content (mg / 100 gꎬ as cyanidin ̄3 ̄O ̄glucose
equivalent)ꎬ A = [A520 nm (pH 1 0) - A700 nm
(pH 1 0)] - [A520 nm (pH 4 5) - A700 nm
(pH 4 5)]ꎬ DF for dilution factorꎬ V for final
volume (mL)ꎬ L for optical path (1 cm)ꎬ and Wt
for sample weight (g) . Anthocyanin concentra ̄
tion was calculated as cyanidin ̄3 ̄glucoside fol ̄
lowing the method of Wrolstad et al. (1982) [20]ꎬ
with a molar absorptivity (ε) of 26 900 and a mo ̄
lecular weight (MW) of 449 2. Three measure ̄
ments for each biological replicate sample were
performed.
1 2 2 Isolation of anthocyanin biosynthetic genes
Sequences of anthocyanin biosynthetic genes
in Arabidopsis were BLASTed against the ge ̄
nome sequence of B. rapa ( http: / / brassi ̄
cadb org / brad / blastPage php ) . Homologous
sequences were recovered and used to design
primers to amplify cDNA derived from the petiole
epidermis of Hongcaitai. The PCR products were
purified and cloned into pEASY ̄T1 vector using
TA cloning kit ( TransGen Biotech ) . Plasmid
DNAs were extracted using a Plasmid Mini kit
(Zoman) and then subjected to sequencing.
1 2 3 RNA extractionꎬ cDNA synthesis and real ̄
time PCR analysis
Total RNA was extracted using a GREENspin
plant RNA extraction kit (Zomanbioꎬ Beijingꎬ Chi ̄
na) according to the manufacturers manual. The
RNA samples were treated with DNaseI (TaKa ̄
Raꎬ Kyotoꎬ Japan) to remove DNA contamina ̄
tion. Approximately 1 μg of total RNA was subjec ̄
ted to first ̄strand cDNA synthesis using an oligo ̄
dT primer ( Takara) and PrimeScript® Reverse
Transcriptase (Takara) .
Real ̄time PCR analysis was conducted using
the 7500 Fast Real ̄Time PCR System (Applied
Biosystems) . All reactions were performed using
SYBR® Premix Ex TaqTMⅡ (Takara) according to
the manufacturers instructions. Reactions were
carried out in a total volume of 20 μL reaction mix ̄
ture containing 10 0 μL of 2 × SYBR Green Ⅰ
Master Mix (Takara)ꎬ 0 2 μmol / L of each primerꎬ
and 100 ng of template cDNA. PCR amplification
was performed using two ̄step cycling conditions
of 95℃ for 30 sꎬ followed by 40 cycles of 95℃ for
3 s and 60℃ for 30 s. A BrEF1A gene in B. rapa
was used as a constitutive control[21] . Melting
curve analysis was performed at the end of 40
cycles to ensure proper amplification of target
fragments. Fluorescence readings were consecu ̄
tively collected during the melting process from
60℃ to 90℃ at a heating rate of 0 5℃/ s. Reac ̄
tion mixtures without cDNA templates were also
run as a negative control. The relative quantities
of the transcripts were calculated using the com ̄
parative Ct method. All analyses were repeated
with three biological replicates.
2 Results
2 1 Genes involved in anthocyanin biosynthesis
in B. rapa
Sequences of genes involved in Arabidopsis
anthocyanin biosynthesis were compared against
the genome sequence of B. rapa line Chiifu ̄401.
Fourꎬ twoꎬ oneꎬ twoꎬ oneꎬ twoꎬ and one copy of
genes encoding CHSꎬ CHIꎬ F3′Hꎬ F3Hꎬ DFRꎬ
LDOXꎬ and UFGTꎬ respectivelyꎬ were identified.
The different copies of CHSꎬ CHIꎬ F3Hꎬ and
LDOX gene families shared 90%ꎬ 89%ꎬ 92%ꎬ
and 93% identities in coding DNA sequencesꎬ re ̄
spectively. In additionꎬ threeꎬ oneꎬ and two homo ̄
793 第 4期 魏国超等: 冬性植物红菜薹在不同温度处理下花青素积累的分子机制(英文)
logues of Arabidopsis AtMYB75ꎬ AtTTG1 and At ̄
EGL3ꎬ respectivelyꎬ were also identified in the
genome of Chiifu ̄401. The three MYBA genesꎬ
designated BrMYBA1ꎬ BrMYBA2ꎬ BrMYBA3ꎬ
shared 87% identity in coding DNA sequences.
The two bHLH genesꎬ designated BrbHLH1 and
BrbHLH2ꎬ showed 90% identity in coding DNA
sequences.
To reveal the level of coding DNA sequence
identities between Hongcaitai and Chiifu ̄401ꎬ
conserved sequences of each gene family were
used to design primers to amplify cDNAs from
petiole epidermal tissues. As a resultꎬ 10 cDNA
fragments of anthocyanin biosynthetic genes
were cloned and sequenced. The cDNA frag ̄
ments ranged from 572 to 945 bp in size. Ove ̄
rallꎬ anthocyanin biosynthetic genes in Hongcaitai
showed over 98% identities in coding DNA se ̄
quences with those in Chiifu ̄401. The sequence
differences all arose from single nucleotide poly ̄
morphisms (SNPs) . This indicated that Hongcai ̄
tai was closely related to Chiifu ̄401ꎬ and the refe ̄
rence genome of Chiifu ̄401 could be used to de ̄
sign primers to analyze expression profiles of
genes in Hongcaitai. In additionꎬ phylogenetic
analysis indicated that BrMYBAꎬ BrbHLHꎬ and
BrWD40 genes in B. rapa were closely related to
anthocyanin regulatory genes found in other plant
species such as appleꎬ grapevineꎬ and petunia
(Fig 2) .
0.05 0.05 0.05
81
92
93
100 59
99
100 100
100
73
89
67
100
100
100
91
99
96
100
100
100
100
99
99
75
74
31
29
51
100
100 100
100
100
100
100
100
BrMYBA1
BrMYBA2
BrMYBA3
AtMYB75
AtMYB90
AtMYB113
AtMYB114
PhAN2
ROSEA2
ROSEA1
VvMYBA1
VvMYBA2
MdMYB10
MdMYBA
MdMYB1
AtTT2
DkMYB2
DkMYB4
VvMYBPA1
AtMYB111
VvMYBF1
AtMYB12
AtMYB11
PfMYC-Rp
AmDEL
PhJAF13
VvMYCA1
MdbHLH33
AtGL3
AtEGL3
BrbHLH1
BrbHLH2
OsRa
ZmLc
ZmB
AtTT8
PhAN1
MdbHLH3
GhTTG1
MdTTG1
VvWDR1
PhAN11
BrWD40
AtTTG1
ZmPAC1
ZmMP1
AtAN11
VvWDR2
A B C
Aꎬ Bꎬ and C represent MYBꎬ bHLHꎬ and WD40ꎬ respectivelyꎬ and the genes in B. rapa are highlighted in black bold. GenBank ac ̄
cession numbers of the sequences are as follows: AtMYB113 (NM105308)ꎬ AtMYB75 (NM_104541)ꎬ AtMYB90 (NP176813)ꎬ Md ̄
MYBA (AB279598)ꎬ MdMYB1 (ABK58136)ꎬ MdMYB10 (ABB84754)ꎬ VvMYBA1 (AB242302)ꎬ VvMYBA2 (AB097924)ꎬ PhAN2
(AAF66727 )ꎬ ROSEA1 ( ABB83826 )ꎬ ROSEA2 ( ABB83827 )ꎬ AtTT2 ( NM _ 122946 )ꎬ DkMYB4 ( AB503701 )ꎬ DkMYB2
(AB503699)ꎬ VvMYBPA1 (AM259485)ꎬ VvMYBF1 (FJ948477)ꎬ AtMYB11 (NP_191820)ꎬ AtMYB12 (NM_130314)ꎬ AtMYB111
(NM_124310)ꎬ AtEGL3 (NP_176552)ꎬ AtGL3 (NP_680372)ꎬ VvMYCA1 (ABM92332)ꎬ PhAN1 (AAG25928)ꎬ AtTT8 (CAC14865)ꎬ
ZmB ( CAA40544 )ꎬ ZmLc ( ABD72707 )ꎬ OsRa ( AAC49219 )ꎬ AmDEL ( AAA32663 )ꎬ PfMYC ̄Rp ( BAA75513 )ꎬ PhJAF13
(AAC39455)ꎬ MdbHLH3 ( ADL36597 )ꎬ MdbHLH33 ( DQ266451 )ꎬ AtTTG1 ( NP_ 851070 )ꎬ ZmMP1 ( AAR01949 )ꎬ GhTTG1
(AAM95641 )ꎬ AtAN11 ( AAC18912 )ꎬ ZmPAC1 ( AAM76742 )ꎬ MdTTG1 ( AAF27919 )ꎬ PhAN11 ( AAC18914 )ꎬ VvWDR1
(ABF66625)ꎬ VvWDR2 (ABF66626) .
Fig 2 Phylogenetic trees derived from amino acid sequences of anthocyanin regulatory genes in plants
893 植 物 科 学 学 报 第 32卷
2 2 Anthocyanin content in leaves and petioles
of B. rapa
Anthocyanin accumulation was detected in
leaves and petiole epidermal tissues of Hongcai ̄
tai seedlings grown at 20℃ (Table 1) . The petio ̄
le endodermis was green in color and did not ac ̄
cumulate anthocyanin. The anthocyanin level in
petiole epidermis was almost 7 ̄fold higher than
that in leaf tissues (with excised mid ̄rib veins) .
In contrastꎬ anthocyanins were not detectable in
the leafꎬ petiole epidermisꎬ and petiole endoder ̄
mis of Chinese cabbage seedlings grown at
20℃.
To assess patterns of anthocyanin accumula ̄
tion during the winter growing seasonꎬ seedlings
of Hongcaitai and Chinese cabbage were further
subjected to two consecutive treatments of cold
stress. The anthocyanin concentration increased
up to 2 78 ̄fold in the petiole epidermis of Hong ̄
caitai after a 7 d cold stress at 10℃ꎬ and in ̄
creased slightly (up to 124 ̄fold) after an addi ̄
tional cold stress at 2℃ for 7 d. Leaves of Hong ̄
caitai showed a slight increase in anthocyanin
content (up to 157 ̄fold) after a period of 7 d
cold stress at 10℃ꎬ but without an increase in
anthocyanin accumulation after an additional 7 d
period of cold stress at 2℃. Cold stress treat ̄
ments at 10℃ and 2℃ did not induce anthocya ̄
nin accumulation in the leaves or petioles of Chi ̄
nese cabbage.
2. 3 Expression profiling of anthocyanin biosyn ̄
thetic genes in B. rapa
Initiallyꎬ expression profiles of anthocyanin
biosynthetic genes were investigated in seedlings
of Hongcaitai grown at 20℃. RT ̄PCR analysis re ̄
vealed that transcripts of four genesꎬ BrCHS4ꎬ
BrF3H2ꎬ BrMYBA2ꎬ and BrMYBA3ꎬ were not de ̄
tected in petiole epidermal tissuesꎬ and thus
these genes were not included in further analysis.
Subsequentlyꎬ qRT ̄PCR analysis revealed that
transcripts of anthocyanin biosynthetic genes
were mainly accumulated in leaf and petiole epi ̄
dermal tissues (Fig 3) . Expression levels of an ̄
thocyanin biosynthetic genes were significantly
higher in petiole epidermal tissues than in leaves.
For exampleꎬ transcript levels of BrDFRꎬ BrL ̄
DOX1ꎬ and BrUFGT in petiole epidermal tissues
were 481 ̄ꎬ 120 ̄ꎬ and 18 ̄fold higher than those in
leavesꎬ respectively. BrF3′H and BrLDOX2 were
exclusively expressed in petiole epidermal tis ̄
suesꎬ though the expression level of BrLDOX2
was very low. For anthocyanin regulatory genesꎬ
BrMYBA1 was exclusively expressed in petiole
epidermal tissuesꎬ BrbHLH1 was expressed in
both leaf and petiole epidermisꎬ and BrbHLH2
was expressed at very low levels in petiole epi ̄
dermal tissuesꎬ but was not detectable in leaf
and petiole endodermal tissues. BrWD40 tran ̄
scripts accumulated in all analyzed tissuesꎬ in ̄
cluding leaf and petiole epidermal and endoder ̄
mal tissues.
As mentioned aboveꎬ anthocyanins were not
detected in leaves and petioles of Chinese cab ̄
bageꎻ thereforeꎬ the petiole epidermis of Chinese
cabbage was selected for gene expression ana ̄
lysisꎬ and no transcripts of anthocyanin pathway
Table 1 Anthocyanin concentration (mg / 100 g) in leaf and petiole in B. rapa vegetables
Treatment
Chinese cabbage Hongcaitai
Leaf Petiole epidermis Petiole endodermis Leaf Petiole epidermis Petiole endodermis
T1 N / D N / D N / D 5. 26 ± 0. 53 34. 79 ± 0. 53 N / D
T2 N / D N / D N / D 8. 27 ± 1. 06 96. 58 ± 0. 53 N / D
T3 N / D N / D N / D 8. 27 ± 1. 06 119. 4 ± 0. 00 N / D
Note: T1: A period of 7 d growth at 20℃ꎻ T2: A period of 7 d cold stress at 10℃ after T1 treatmentꎻ T3: An additional 7 d period of
cold stress at 2℃ after T2 treatment. Values represent average of three replicates. N / D: not detectable.
993 第 4期 魏国超等: 冬性植物红菜薹在不同温度处理下花青素积累的分子机制(英文)
PEC: Petiole epidermal tissues of Chinese cabbageꎻ PENH: Petiole endodermal tissues of Hongcaitaiꎻ LH: Leaves (with excised
mid ̄rib veins) of Hongcaitaiꎻ PEPH: Petiole epidermal tissues of Hongcaitai.
Fig 3 qRT ̄PCR analysis of anthocyanin biosynthetic genes in Hongcaitai and Chinese cabbage seedlings grown at 20℃
genes were detected. BrWD40 was expressed at
a low level in petiole epidermisꎬ while transcripts
of BrMYBA1ꎬ BrbHLH1ꎬ and BrbHLH2 were not
detected in petiole epidermis.
2. 4 Effect of cold temperatures on the expres ̄
sion of anthocyanin biosynthetic genes in petiole
epidermis of Hongcaitai
As seedlings of Hongcaitai accumulated an ̄
thocyanins in the petiole epidermisꎬ expression of
anthocyanin biosynthetic genes in response to
cold temperatures was only conducted in this tis ̄
sue. Structural genes of the anthocyanin path ̄
way showed reduced transcript levels following
cold treatment ( Fig 4 ) . Transcription levels of
BrCHS1ꎬ BrCHS2ꎬ BrCHS3ꎬ BrCHI1ꎬ BrCHI2ꎬ
BrF3′Hꎬ BrF3H1ꎬ BrDFRꎬ BrLDOX1ꎬ BrLDOX2ꎬ
and BrUFGT in petiole epidermal tissues after 7 d
growth at 10℃ decreased by 38%ꎬ 54%ꎬ 12%ꎬ
3%ꎬ 63%ꎬ 1%ꎬ 58%ꎬ 41%ꎬ 2%ꎬ 28%ꎬ and 62%ꎬ
respectivelyꎬ compared to those in tissues grown
at 20℃ for 7 d. Similarlyꎬ transcript levels of
BrCHS1ꎬ BrCHS2ꎬ BrCHS3ꎬ BrCHI1ꎬ BrCHI2ꎬ
BrF3′Hꎬ BrF3H1ꎬ BrDFRꎬ BrLDOX1ꎬ BrLDOX2ꎬ
and BrUFGT in petiole epidermal tissues after an
additional treatment at 2℃ for 7 d decreased sig ̄
nificantly by 83%ꎬ 56%ꎬ 81%ꎬ 64%ꎬ 77%ꎬ 59%ꎬ
88%ꎬ 64%ꎬ 88%ꎬ 68%ꎬ and 77%ꎬ respectivelyꎬ
compared to those in tissues grown at 20℃ for
7 d. On averageꎬ transcript levels of anthocyanin
structural genes decreased by 33% and 73% af ̄
ter cold treatment at 10℃ for 7 d and subsequent ̄
cold treatment at 2℃ for 7 dꎬ respectivelyꎬ com ̄
pared to those in tissues grown at 20℃ for 7 d.
Transcript levels of BrMYBA1 and BrWD40 in
the petiole epidermis after cold treatment at 10℃
for 7 d increased by 85% and 87%ꎬ respectivelyꎬ
compared to those in the petiole epidermis grown
at 20℃ for 7 d. Howeverꎬ transcript levels of
004 植 物 科 学 学 报 第 32卷
T1: A period of 7 d growth at 20℃ꎻ T2: A period of 7 d cold stress at 10℃ after T1 treatmentꎻ T3: An additional
7 d period of cold stress at 2℃ after T2 treatment.
Fig 4 qRT ̄PCR analysis of anthocyanin structural genes in petiole epidermis
of Hongcaitai seedlings under cold treatment
BrbHLH1 and BrbHLH2 in petiole epidermal tis ̄
sues after 7 d growth at 10℃ decreased signifi ̄
cantly by 93% and 92%ꎬ respectivelyꎬ compared
to those in tissues grown at 20℃ for 7 d. Tran ̄
script levels of BrMYBA1ꎬ BrbHLH1ꎬ BrbHLH2ꎬ
and BrWD40 in petiole epidermal tissues after
subsequent cold treatment at 2℃ for 7 d de ̄
creased by 72%ꎬ 96%ꎬ 80%ꎬ and 25%ꎬ respec ̄
tivelyꎬ compared to those in tissues grown at
20℃ for 7 d (Fig 5) .
3 Discussion
3 1 Mechanism underlying the regulation of an ̄
thocyanin pigmentation in Hongcaitai
In this studyꎬ we report for the first time on the
mechanism underlying anthocyanin pigmentation in
104 第 4期 魏国超等: 冬性植物红菜薹在不同温度处理下花青素积累的分子机制(英文)
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T1 T1T2 T2T3 T3
Treatment Treatment
BrMYBA1
BrBHLH2
BrbHLH1
BrWD40
T1: A period of 7 d growth at 20℃ꎻ T2: A period of 7 d cold stress at 10℃ after T1 treatmentꎻ T3: An additional
7 d period of cold stress at 2℃ after T2 treatment.
Fig 5 qRT ̄PCR analysis of anthocyanin regulatory genes in petiole epidermal
tissues of Hongcaitai seedlings under cold treatment
Chinese vegetable Hongcaitai. Seedlings of
Hongcaitai grown at 20℃ accumulated anthocya ̄
nins in leaf and petiole epidermal tissuesꎬ and
anthocyanin content was about 7 ̄fold higher in
petiole epidermis than in leaf tissues. All structu ̄
ral genes showed higher levels of expression in
petiole epidermis than in both leaf and petiole
endodermal tissues. These findings clearly sug ̄
gest that anthocyanin accumulation in Hongcaitai
is controlled at the transcriptional level. Subse ̄
quentlyꎬ expression of anthocyanin regulatory
genes BrMYBAꎬ BrbHLHꎬ and BrWD40 were de ̄
termined. Transcript levels of BrbHLH and
BrWD40 in petiole epidermal tissues were similar
to those in leaf tissuesꎬ suggesting that BrbHLH
and BrWD40 were not likely responsible for an ̄
thocyanin pigmentation in Hongcaitai. In contrastꎬ
the transcript level of BrMYBA1 in petiole epider ̄
mal tissues was more than 300 ̄fold higher than
that detected in leaf tissues. Thereforeꎬ BrMYBA1
is a likely candidate gene responsible for regula ̄
tion of anthocyanin pigmentation in Hongcaitai.
It is worth noting that BrMYBA1 and three
structural genesꎬ BrF3′Hꎬ BrDFRꎬ and BrLDOX1ꎬ
were expressed at extremely low levels in leaf tis ̄
suesꎬ but were highly expressed in petiole epi ̄
dermal tissues. In purple ̄colored cauliflower
(Brassica oleracea var. botrytis)ꎬ the MYB TF
BoMYB2 specifically activates BobHLH1 along
with a subset of anthocyanin structural genesꎬ
including BoF3′Hꎬ BoDFRꎬ and BoLDOX[22] . BrMY ̄
BA1 and BoMYB2 shared 98% identity in coding
DNA sequences. Interestinglyꎬ Hongcaitai and
purple cauliflower have the same ancestor and
belong to the same genusꎬ Brassica. Thusꎬ it is
reasonable to speculate that BrMYBA1ꎬ like Bo ̄
MYB2ꎬ may also have the ability to activate the
regulatory gene BrbHLH as well as such structu ̄
ral genes as BrF3′Hꎬ BrDFRꎬ and BrLDOX1. This
comparative analysis of anthocyanin biosynthesis
genes between B. rapa and B. oleracea further
supports our proposal that BrMYBA1 is responsi ̄
ble for the regulation of anthocyanin accumulation
in Hongcaitai.
If anthocyanin biosynthesis in Hongcaitai is
indeed controlled by BrMYBA1ꎬ then the question
arises as to whether anthocyanin accumulation
occurs in the leaves of Hongcaitai. In this studyꎬ
transcripts of BrMYBA1 were almost undetectable
in leaf tissuesꎻ howeverꎬ leaves had low levels of
anthocyanin accumulation. Transcript levels of
upstream genes in the anthocyanin biosynthesis
204 植 物 科 学 学 报 第 32卷
pathwayꎬ including BrCHS1ꎬ BrCHS3ꎬ and Br ̄
CHI2ꎬ were relatively highly expressed in leaf tis ̄
sues. In Arabidopsisꎬ three closely ̄related MYB
TFsꎬ including AtMYB11ꎬ AtMYB12ꎬ and At ̄
MYB111ꎬ regulate transcription of genes AtCHS
and AtCHI[23] . Thusꎬ we cannot exclude the pos ̄
sibility that other regulatory genes may also be in ̄
volved in the regulation of anthocyanin biosynthe ̄
sis in Hongcaitai. Moreoverꎬ transcripts of BrF3′H
were almost undetectable in leaf tissues. It is
known that the F3′H gene plays an important role
in the hydroxylation of anthocyaninsꎬ and it is in ̄
volved in the production of cyanidin ̄based pig ̄
ments[24ꎬ25] . In addition to F3′Hꎬ F3H and F3′5′H
are also involved in hydroxylation of anthocya ̄
ninsꎬ leading to the generation of pelargonidin ̄
and delphinidin ̄based pigmentsꎬ respectively[2] .
Because Hongcaitai mainly accumulates cyani ̄
din ̄based anthocyanins[26]ꎬ there is no F3′5′H
gene present in the B. rapa genome[21] . BrF3H
was expressed at low levels in leaves of Hongcai ̄
tai. Thusꎬ it seems likely that leaves accumulated
only pelargonidin ̄based anthocyaninsꎬ while pe ̄
tiole epidermis contained both cyanidin ̄and pe ̄
largonidin ̄based anthocyanins in Hongcaitai. In
additionꎬ it is important to note that the mid ̄rib
vein was red in colorꎬ and thus contained anthoc ̄
yanins. The possibility cannot be excluded that
anthocyanin accumulation in leaves of Hongcaitai
is partially attributed to movement of anthocya ̄
nins from mid ̄rib veins to the mesophyll.
RBr ( rapid ̄cycling B. rapa) are anthocya ̄
ninless (anl) mutants of B. rapa that do not pro ̄
duce anthocyanin pigments. The anl locus has
been mapped to B. rapa linkage group 9[27] . In
this study BrMYBA1ꎬ located on linkage group 7ꎬ
was likely responsible for the regulation of antho ̄
cyanins in Hongcaitai. The other two BrMYBA
genesꎬ BrMYBA2 and BrMYBA3ꎬ were located
on linkage groups 3 and 2ꎬ respectively. These
results suggest that genes other than BrMYBA
may also play important roles in the regulation of
anthocyanin biosynthesis in B. rapa. BrbHLH1ꎬ
BrbHLH2 and BrDFR were all located on linkage
group 9ꎬ and may be candidate genes for the anl
locus.
3 2 Effect of cold temperatures on anthocyanin
pigmentation in Hongcaitai seedlings
It has been widely reported that low tempe ̄
ratures induce transcription of anthocyanin bio ̄
synthetic genesꎬ leading to increased accumula ̄
tion of anthocyanins in plants[14ꎬ17] . Howeverꎬ the
effect of low temperatures on anthocyanin accu ̄
mulation has not been reported in any winter
plants. In this studyꎬ we investigated the effects
of cold temperatures on anthocyanin accumula ̄
tion in seedlings of a winter vegetableꎬ Hongcai ̄
tai. The anthocyanin content in petiole epidermis
increased after one or two weeks of growth at
cold temperature. This finding was consistent with
the fact that red pigmentation in Hongcaitai in ̄
creases as temperature drops in the winter gro ̄
wing season. Howeverꎬ transcript levels of antho ̄
cyanin structural genes decreased in the petiole
epidermis after one or two weeks of growth at
cold temperatures. This was similar to the finding
that high temperatures inhibit the transcription of
anthocyanin biosynthetic genes[7] . High tempera ̄
tures increase the degradation of anthocya ̄
nins[12]ꎬ while anthocyanins are stable at low
temperatures[28] . Thereforeꎬ the stability of antho ̄
cyanins is likely responsible for the increased ac ̄
cumulation of anthocyanins in the petiole epider ̄
mis of Hongcaitai grown under cold tempera ̄
tures.
Unlike anthocyanin structural genesꎬ the regu ̄
latory genes BrMYBA1 and BrWD40 were ex ̄
pressed at higher levels in the petiole epidermis
of Hongcaitai at 10℃ than in the petiole epider ̄
mis grown at 2℃. Howeverꎬ transcript levels of
304 第 4期 魏国超等: 冬性植物红菜薹在不同温度处理下花青素积累的分子机制(英文)
BrbHLH1 in the petiole epidermis at 10℃ de ̄
creased significantly compared to that of
BrbHLH1 in the petiole epidermis at 20℃. While
overexpression of Myb113 or Myb114 upregula ̄
ted the anthocyanin pathway and is bHLH ̄de ̄
pendent in Arabidopsisꎬ it seems likely that the
decreased transcript levels of BrbHLH1 reduced
the transcript levels of BrMYBA1[29] . This finding
was in contrast to previous reports indicating that
low temperature (17℃) induced the expression
of bHLH in apple fruits[17] . This may be attributed
to differences in both temperature and plant spe ̄
cies. Transcription of anthocyanin structural
genes are regulated via the combinatorial actions
of MYBꎬ bHLHꎬ and WD40 proteins[2] . Thusꎬ it is
clear that inhibition of the transcription of anthoc ̄
yanin structural genes in the petiole epidermis at
10℃ was probably caused by lower transcript
levels of BrbHLH1. Moreoverꎬ the transcription of
all regulatory genesꎬ including BrMYBA1ꎬ
BrbHLH1ꎬ and BrWD40ꎬ were significantly inhibi ̄
ted in the petiole epidermis of Hongcaitai grown
at 2℃ꎬ leading to a significant decrease in the
expression of anthocyanin structural genes. This
was consistent with our finding that anthocyanin
content in the petiole epidermis of Hongcaitai
showed a slight increase after a 7 d growth at 2℃.
In briefꎬ this study reports for the first time on
the mechanism underlying the regulation of an ̄
thocyanin accumulation in Hongcaitai. Anthocya ̄
nin pigmentation in Hongcaitai appeared to be
controlled by BrMYBA1. The petiole epidermis of
Hongcaitai grown at cold temperatures showed
increased accumulation of anthocyaninꎬ although
the transcription of anthocyanin biosynthetic
genes was inhibited.
Acknowledgements: We greatly thank Schuyler S
Korban for critical revision of this manuscript.
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504 第 4期 魏国超等: 冬性植物红菜薹在不同温度处理下花青素积累的分子机制(英文)