生物工程学报  2024, Vol. 40 Issue (1): 239-251
http://dx.doi.org/10.13345/j.cjb.230287
中国科学院微生物研究所、中国微生物学会主办
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文章信息

秦孝天, 郭梦鸽, 秦少华, 陈瑞丹
QIN Xiaotian, GUO Mengge, QIN Shaohua, CHEN Ruidan
梅花新品种‘治章骨红重翠’跨品种群特性机制探究
Exploration of cross-cultivar group characteristics of a new cultivar of Prunus mume 'Zhizhang Guhong Chongcui'
生物工程学报, 2024, 40(1): 239-251
Chinese Journal of Biotechnology, 2024, 40(1): 239-251
10.13345/j.cjb.230287

文章历史

Received: April 15, 2023
Accepted: August 23, 2023
Published: August 28, 2023
梅花新品种‘治章骨红重翠’跨品种群特性机制探究
秦孝天1,2 , 郭梦鸽1 , 秦少华2 , 陈瑞丹1     
1. 北京林业大学园林学院 国家花卉工程技术研究中心 园林环境教育部工程研究中心 花卉种质创新与分子育种北京市重点试验室 城乡生态环境北京试验室 林木花卉遗传育种教育部重点试验室, 北京 100083;
2. 豫西梅花研究所, 河南 三门峡 472200
摘要:‘治章骨红重翠’梅是一个具有跨品种群特性的梅花新品种,它同时具有朱砂和绿萼品种群的典型特征,其萼绿、花白、木质部淡暗紫色,但其机制并不清楚。本研究对‘治章骨红重翠’梅、‘豫西朱砂’梅、‘豫西变绿萼’梅表型、花色苷含量和花青素合成通路相关基因的表达量进行测定,结果表明,花瓣、萼片和枝内新生木质部的红色程度与总花色苷含量呈正相关。MYBɑ1MYB1bHLH3是影响这3个品种花部与木质部呈现红色的关键转录因子基因,转录因子促进结构基因F3′HDFRANSUFGT高表达,从而促进红色性状的产生。综合分析后推测,‘治章骨红重翠’梅花瓣白色源于矢车菊合成通路上其他分支FLSF3′5′HLARANR基因高表达,谷胱甘肽转移酶(glutathione transferase, GST)基因GST低表达;萼片绿色源于F3′HDFRANS基因低表达;木质部红色源于ANSUFGT基因高表达。本研究对‘治章骨红重翠’梅跨品种群特性作出初步解释,为梅花花色与木质部颜色的分子育种提供了参考。
关键词    跨品种群    实时荧光定量PCR    花色    木质部颜色    
Exploration of cross-cultivar group characteristics of a new cultivar of Prunus mume 'Zhizhang Guhong Chongcui'
QIN Xiaotian1,2 , GUO Mengge1 , QIN Shaohua2 , CHEN Ruidan1     
1. Beijing Key Laboratory of Ornamental Plants Germplasm Innovation & Molecular Breeding, Beijing Laboratory of Urban and Rural Ecological Environment, Key Laboratory of Genetics and Breeding in Forest Trees and Ornamental Plants of Ministry of Education, National Engineering Research Center for Floriculture, Engineering Research Center of Landscape Environment of Ministry of Education, School of Landscape Architecture, Beijing Forestry University, Beijing 100083, China;
2. Yuxi Institute of Mei, Sanmenxia 472200, Henan, China
Abstract: 'Zhizhang Guhong Chongcui' is a new cultivar of Prunus mume with cross-cultivar group characteristics. It has typical characteristics of cinnabar purple cultivar group and green calyx cultivar group. It has green calyx, white flower, and light purple xylem, but the mechanism remains unclear. In order to clarify the causes of its cross-cultivar group traits, the color phenotype, anthocyanin content and the expression levels of genes related to anthocyanin synthesis pathway of 'Zhizhang Guhong Chongcui', 'Yuxi Zhusha' and 'Yuxi Bian Lü'e' were determined. It was found that the red degree of petals, sepals and fresh xylem in branches was positively correlated with the total anthocyanin content. MYBɑ1, MYB1, and bHLH3 were the key transcription factor genes that affected the redness of the three cultivars of flowers and xylem. The transcription factors further promoted the high expression of structural genes F3′H, DFR, ANS and UFGT, thereby promoting the production of red traits. Combined with phenotype, anthocyanin content and qRT-PCR results, it was speculated that the white color of petals of 'Zhizhang Guhong Chongcui' were derived from the high expression of FLS, F3′5′H, LAR and ANR genes in other branches of cyanidin synthesis pathway, and the low expression of GST gene. The green color of sepals might be originated from the relatively low expression of F3′H, DFR and ANS genes. The red color of xylem might be derived from the high expression of ANS and UFGT genes. This study made a preliminary explanation for the characteristics of the cross-cultivar group of 'Zhizhang Guhong Chongcui', and provided a reference for molecular breeding of flower color and xylem color of Prunus mume.
Keywords: Prunus mume    cross-cultivar group    real-time quantitative PCR    flower color    xylem color    

花色与木质部颜色是观赏植物重要的品质性状与品种分类指标。在植物的根、茎、叶、花和果实等器官中含有不同种类与含量的颜色物质,它们主要为花青素、类胡萝卜素和甜菜素[1]。作为类黄酮的一员,花青素是一类广泛存在于自然界植物中的水溶性色素,常存在于液泡中,与糖结合以花色苷的形式表现出丰富的颜色类型。植物中常见的花色素分为6类:天竺葵色素、矢车菊色素、飞燕草色素、芍药色素、矮牵牛色素和锦葵色素。因其在植物中性状及功能多样,花青素在观赏植物中受到了越来越多的关注与研究[2]

目前,花青素生物合成途径已在拟南芥等植物中进行了广泛的研究。首先,苯丙氨酸在苯丙氨酸解氨酶(phenylalanine ammonia-lyase, PAL)、肉桂酸-4-羟化酶(cinnamate-4-hydroxylase, C4H)、4-香豆酸: 辅酶A连接酶(4-coumarate: coenzyme A ligase, 4CL)的催化下生成4-香豆酰CoA,其与3个丙二酰CoA结合,在查尔酮合酶(chalcone synthase, CHS)的催化下生成查尔酮。然后,查尔酮在查尔酮异构酶(chalcone isomerase, CHI)、黄烷酮3-羟化酶(flavanone 3-hydroxylase, F3H)、类黄酮3′-羟化酶(flavonoid 3′-hydroxylase, F3′H)、二氢黄酮醇4-还原酶(dihydroflavonol 4-reductase, DFR)和花青素合成酶(anthocyanin synthase, ANS)等酶的依次催化下,形成无色花青素,继而在糖基转移酶(glycosyltransferase, GT)、甲基转移酶(methyltransferase, MT)等酶的催化下进行糖基化与甲基化修饰,生成有色的稳定花色苷。随后,在谷胱甘肽转移酶(glutathione transferase, GST)的参与下,花色苷转运至液泡中实现储存与最终呈色[3-5]。有研究发现,类黄酮糖基转移酶(uridine diphosphate flavonoid 3-O-glucosyltransferase, UFGT)在红花中的活性显著高于白花,且与花色素苷积累量的变化一致,表明UFGT是梅花红色花形成的关键基因[6]

除了上述结构基因外,转录因子对花色素合成及花色呈现起重要作用。转录因子通过激活或抑制结构基因的表达,从而实现对花青素生物合成途径的调控,最终提高或降低植物细胞中的花色苷含量。许多研究表明,MYB、bHLH、WD40等是花青素生物合成的重要转录因子,它们常形成MYB-bHLH-WD repeat (MBW)复合体,通过与启动子结合,调控花青素通路结构基因的表达[7]。张启翔等在梅花全基因组重测序研究中发现,MYB108编码一个R2R3-MYB转录因子,与木质部颜色正相关[8]PmMYBa1在富含花青素的红色花中的表达量高于白色花,并与梅花花瓣发育中的花青素含量密切相关,通过在烟草中过表达发现该基因在花色苷合成过程中起重要调控作用[9-10]

作为中国传统名花,梅(Prunus mume)的应用与栽培历史悠久,有着极为深厚的文化底蕴与精神含义。在梅花11个品种群的分类体系下,朱砂品种群的典型分类特征是花瓣红色、萼片绛紫色与枝内新生木质部淡暗紫色;绿萼品种群的典型分类特征是花瓣白色、萼片绿色、枝内新生木质部绿白色[11]。在豫西梅园的栽培实践中,发现了一个兼具朱砂品种群特征和绿萼品种群特征的新品种——‘治章骨红重翠’[12],它与朱砂品种群有相同的红色木质部,与绿萼品种群有相同的白花绿萼。然而,‘治章骨红重翠’这些性状形成的原因尚不清楚,其分类地位也不明晰。

目前,对梅花花青素的研究主要集中于花部性状,对木质部的研究报道较少。有研究认为梅花花色苷的代谢途径主要是矢车菊素分支[9-10],选择了这一分支的7个结构基因[2],选择了在梅花中报道过的4个转录因子基因[9-10, 13-14],进行实时荧光定量PCR检测,从花瓣、萼片与枝内新生木质部颜色3个点出发,在转录水平上对影响‘治章骨红重翠’梅跨品种群特性形成的可能的关键结构基因与转录因子基因进行了表达量验证,探究了‘治章骨红重翠’梅品种特性产生的分子机制。本研究结果可为相似品种的产生机制提供有价值的信息,为梅花花色与木质部颜色分子育种提供参考。

1 材料与方法 1.1 试验材料

于2022年3月中下旬在豫西梅花研究所采集‘豫西变绿萼’ ‘治章骨红重翠’ ‘豫西朱砂’ 3个梅花品种的花瓣、萼片及木质。采完样后,迅速放入干冰桶中,后转运至−80 ℃超低温冰箱进行保存。花瓣依照开花阶段分为S1、S2、S3和S4时期(图 1),4个时期的划分主要依据花径与花药散粉状况,S1的花径为0.8−1.1 cm,S2的花径为1.2−1.8 cm,S3与S4的花径为1.9 cm以上,S4存在花瓣明显褪色衰败,S1与S2的花药无散粉,S3的花药有部分散粉,S4为完全散粉并有衰败。萼片取S3盛花时期,枝内新生木质分为一年生和多年生枝条进行采集。

图 1 ‘治章骨红重翠’ ‘豫西朱砂’和‘豫西变绿萼’的花瓣、萼片和木质部颜色性状对比 Fig. 1 Comparison of petals, sepals and xylem color traits among 'Zhizhang Guhong Chongcui', 'Yuxi Zhusha' and 'Yuxi Bian Lü'e'. S1, S2, S3 and S4 refer to stages of bud, initial flowering, flowering, and end of flowering respectively; Sepal: Sepal color of different cultivars; Xylem: Xylem color of transverse section of branches. S1、S2、S3和S4依次指花的蕾期、初开期、盛开期和末花期;Sepal:萼片;Xylem:木质部
1.2 颜色表型测定

对于采集的‘豫西变绿萼’ ‘治章骨红重翠’ ‘豫西朱砂’的花瓣、萼片及新生木质部切片进行花色表型测定,使用NF555色差仪,记录其明度L*值、色相a*值、色相b*值。选择黑色背景板,将花瓣剥离下来充分混合,在花瓣区域随机取5个以上的区域进行数据测量,后取其平均值作为该品种花色数据。用相同的方法进行萼片颜色表型测定。用刀刮去枝条周皮,露出新生木质部,将刀片用酒精润洗后,刮取新生木质部薄片,收集薄片平铺于黑色背景板上,不漏缝隙。用色差仪对新生木质部薄片进行颜色测定,测定时随机选取10个区域,取其平均值作为新生木质部颜色表型数据。

1.3 总花色苷含量测定

取出在−80 ℃超低温冰箱中储存的花瓣,取0.1 g置于液氮中充分研磨成粉末状,天平称重后转存到离心管中,用含1%浓盐酸的甲醇溶液(V浓盐酸: V甲醇=1:99)提取,后置于4 ℃冰箱中避光浸提,浸提期间多次摇动离心管保证充分浸提,每浸提24 h观察离心管颜色变化,直到花瓣粉末变为无色,在12 000 r/min条件下离心2 min,取上清液用0.22 µm一次性过滤灭菌器过滤。将上清液转入比色皿中,以浸提液作对照,使用紫外分光光度计测定OD530的值[15],计算总花色苷含量,以mg/g为单位表示,计算方法参考伏静和戴思兰[16],每个样本3次重复。对萼片、木质部采取相同的处理方法。

总花色苷含量(mg/g FW)=(色素浸提液体积×吸光度值)/(吸光系数×试材质量),以mg/g为单位,试验吸光系数为98.2,FW表示鲜重。

1.4 实时荧光定量PCR检测

各品种总RNA提取使用北京天漠生化科技有限公司生产的总RNA提取试剂盒,按试剂盒步骤完成总RNA提取。使用分光光度计和琼脂糖凝胶电泳检测总RNA质量和浓度后,使用北京天漠生化科技有限公司生产的cDNA第一链合成试剂盒进行反转录得到各品种不同部位的cDNA。

选取梅花花色苷矢车菊合成通路上的7个结构基因PmCHSPmCHIPmF3HPmF3′HPmDFRPmANSPmUFGT (图 2);在NCBI网站上进行同属物种花青素合成相关基因比对并结合本课题组研究,选择PmMYB1PmMYBɑ1PmMYB108PmbHLH3[9-10, 13-14],选择Actin作为内参基因[17]

图 2 花青素生物合成矢车菊通路及其他分支[2, 18] Fig. 2 Cyanidin biosynthesis pathway and other branches[2, 18].

在NCBI (https://www.ncbi.nlm.nih.gov)上查询梅花全基因组数据,在以上相关基因序列的基础上,使用Integrated DNA Technologies (https://sg.idtdna.com)进行实时荧光定量PCR引物设计(表 1)。引物由北京天漠生化科技有限公司合成。

表 1 梅花实时荧光定量PCR的引物序列 Table 1 Primers used for real-time quantitative PCR of Prunus mume
Primer names Primer sequences (5′→3′) Size (bp)
PmCHS ACCCACCTTGACAGTTTAGTG 21
PmCHI CGTTAAGTGGAAGGGCAAGAC 21
PmF3′H AGACAGTGAACTTGGCTCAG 20
PmF3H TCGTAAACCCAGCAAAGGAG 20
PmDFR TGGAGCCACTGGTTTTATAGG 21
PmANS TTCTATGAAGGCAAGTGGGTC 21
PmUFGT TCATTCTTCAGCACTTCACAATCC 24
PmMYBɑ1 AAGTCGAGAATTTTAGTACGC 21
PmMYB1 GAAACAGGTGGTCATTGATTGCT 23
PmMYB108 CTCGCTGGGGAAATAGATGGT 21
PmbHLH3 TGGGTGAATGAAGAAGACAGGG 22
Actin TGCTGAGGACATTCAACCCC 20

以cDNA为模板,使用实时荧光定量PCR的方法对选定的花青素合成相关结构基因与转录因子基因表达量进行测定。反应体系为Takara TB Green® Premix Ex Taq,试验在IQ5 Real-Time PCR系统上进行,反应程序为:95 ℃预变性30 s;95 ℃变性5 s,60 ℃延伸30 s,40个循环。每个样品进行3次重复,计算其相对表达量。

2 结果与分析 2.1 颜色表型分析

NF555色差仪测定结果表明(图 3):3个受试品种的明度L*值在4个阶段表现为一直升高或先升高后降低;色相a*值在4个阶段表现为先升高后降低或一直降低;色相b*值在4个阶段表现为先降低后升高或者一直降低。a*代表从绿色到红色的分量,‘豫西朱砂’的红度值显著高于‘豫西变绿萼’和‘治章骨红重翠’;b*代表从蓝色到黄色的分量,‘豫西朱砂’的黄度值显著低于‘豫西变绿萼’和‘治章骨红重翠’。不同品种在花色参数上存在不同的变化趋势。总体而言,颜色表型的测定结果与英国皇家园艺学会比色卡(Royal Horticultural Society Color Chart, RHSCC)和肉眼观测结果较为一致,‘治章骨红重翠’在花瓣和萼片上与绿萼品种相近,在木质部上与朱砂品种相近。

图 3 受试品种的花色参数L*a*b*在4个开花阶段的变化 Fig. 3 The variation of flower color parameters L*, a* and b* of the 3 tested cultivars at four flowering stages. LE: 'Yuxi Bian Lü'e'; CCGH: 'Zhizhang Guhong Chongcui'; ZS: 'Yuxi Zhusha'. S1, S2, S3 and S4 refer to stages of bud, initial flowering, flowering and end of flowering, respectively. LE:‘豫西变绿萼’;CCGH:‘治章骨红重翠’;ZS:‘豫西朱砂’;S1、S2、S3和S4依次指花的蕾期、初开期、盛开期和末花期
2.2 总花色苷含量对比

3个品种4个开花时期的总花色苷含量测定结果表明(表 2),‘治章骨红重翠’在花瓣上仅有微量红色花色苷的积累,‘豫西变绿萼’同样是微量积累,两者较为接近。“红花”的‘豫西朱砂’存在大量红色花色苷的积累,与“萼绿花白”的‘治章骨红重翠’和‘豫西变绿萼’存在显著差异,这与肉眼观察及上述的颜色表型测定结果一致。

表 2 三个品种不同开花阶段总花色苷含量 Table 2 Determination of total anthocyanin content in three cultivars at different flowering stages (mg/g FW)
Cultivars Flowering periods
S1 S2 S3 S4
‘Yuxi Bian Lü’e’ 0.007 2±0.000 6b 0.012 2±0.000 2b 0.007 6±0.000 3b 0.009 1±0.001 8b
‘Zhizhang Guhong Chongcui’ 0.004 9±0.000 5b 0.002 6±0.000 5b 0.001 9±0.000 4b 0.000 7±0.000 3b
‘Yuxi Zhusha’ 0.595 0±0.122 5a 0.866 1±0.012 4a 0.740 5±0.006 2a 0.279 8±0.063 2a
Different lowercase letters indicate significant difference at 0.05 level at the same flowering stage. FW represents fresh weight. S1, S2, S3 and S4 refer to stages of bud, initial flowering, flowering and end of flowering, respectively.

萼片的总花色苷含量测定结果显示(图 4),‘治章骨红重翠’与‘豫西变绿萼’无显著差异,与‘豫西朱砂’存在显著差异。‘治章骨红重翠’在萼片上表现出与绿萼品种相近的性状,这与颜色表型测定结果一致。

图 4 萼片总花色苷含量 Fig. 4 Total anthocyanin content of sepals. LE: 'Yuxi Bian Lü'e'; CCGH: 'Zhizhang Guhong Chongcui'; ZS: 'Yuxi Zhusha'. Different lowercase letters indicate significant differences at 0.05 level among different cultivars. LE:‘豫西变绿萼’;CCGH:‘治章骨红重翠’;ZS:‘豫西朱砂’

枝内新生木质部的总花色苷含量测定结果显示(图 5),‘治章骨红重翠’红色花色苷含量介于‘豫西变绿萼’和‘豫西朱砂’两者之间,‘治章骨红重翠’总花色苷含量高于‘豫西变绿萼’,低于‘豫西朱砂’,这与颜色表型的测定结果一致。

图 5 枝内新生木质部总花色苷含量 Fig. 5 Total anthocyanin content in fresh xylem. LE: 'Yuxi Bian Lü'e'; CCGH: 'Zhizhang Guhong Chongcui'; ZS: 'Yuxi Zhusha'. Different lowercase letters indicate significant differences at 0.05 level among different cultivars. LE:‘豫西变绿萼’;CCGH:‘治章骨红重翠’;ZS:‘豫西朱砂’
2.3 实时荧光定量PCR检测

对3个品种的花瓣、萼片、木质部分别进行矢车菊通路上的结构基因和转录因子基因的实时荧光定量PCR检测。花瓣的结果表明,‘治章骨红重翠’与‘豫西朱砂’的MYBɑ1MYB1bHLH3基因相对表达量均较高(图 6),‘豫西朱砂’的CHSCHIDFRANS基因相对高表达,这可能是影响其花瓣红艳程度的关键结构基因(图 7),MYBɑ1MYB1bHLH3基因通过正向调节DFRANS基因的表达,从而促进红色花色苷的产生。

图 6 不同品种花瓣中花青素合成转录因子相对表达量 Fig. 6 Relative expression levels of anthocyanin synthesis transcription factors in petals of different cultivars. LE: 'Yuxi Bian Lü'e'; CCGH: 'Zhizhang Guhong Chongcui'; ZS: 'Yuxi Zhusha'. Different lowercase letters indicate significant differences at 0.05 level among different cultivars. LE:‘豫西变绿萼’;CCGH:‘治章骨红重翠’;ZS:‘豫西朱砂’
图 7 花瓣、萼片和木质部花青素合成结构基因相对表达量 Fig. 7 Relative expression levels of anthocyanin synthesis structural genes in petals, sepals and xylem. In order, the three columns are the gene expression levels of petals, sepals and xylem. LE: 'Yuxi Bian Lü'e'; CCGH: 'Zhizhang Guhong Chongcui'; ZS: 'Yuxi Zhusha'. Different lowercase letters indicate significant differences at 0.05 level among different cultivars. LE:‘豫西变绿萼’;CCGH:‘治章骨红重翠’;ZS:‘豫西朱砂’

萼片的结果表明,‘治章骨红重翠’的MYBɑ1MYB1基因表达量与‘豫西变绿萼’较为接近,均显著低于‘豫西朱砂’,这与其在表型和总花色苷含量上表现一致(图 8)。结果表明较高的MYBɑ1MYB1bHLH3基因表达量有助于红色花色苷的积累,有助于萼片红色的成色,表现为‘豫西朱砂’的绛紫色,其余2个低表达的品种则为绿色。结构基因中(图 7),绛紫色萼片的‘豫西朱砂’除了在DFR上是低表达外,其余均高表达,表现为整个通路上的高表达,这可能是其萼片绛紫色的成因。‘治章骨红重翠’在F3′HDFR基因的低表达可能是其未能产生足量红色花色苷而呈现出绿色的原因,这些基因的表达状况与前人在红色花瓣中的推论相吻合[15]

图 8 萼片与枝内新生木质部花青素合成转录因子相对表达量 Fig. 8 Relative expression levels of anthocyanin synthesis transcription factors of sepals and fresh xylem. In order, the left column is the gene expression levels of sepals and the right column is the gene expression levels of xylem. LE: 'Yuxi Bian Lü'e'; CCGH: 'Zhizhang Guhong Chongcui'; ZS: 'Yuxi Zhusha'. Different lowercase letters indicate significant differences at 0.05 level among different cultivars. LE:‘豫西变绿萼’;CCGH:‘治章骨红重翠’;ZS:‘豫西朱砂’

实时荧光定量PCR检测结果表明,‘治章骨红重翠’枝条的新生木质部MYBɑ1MYB1基因与花色苷含量趋势高度一致,bHLH3在‘治章骨红重翠’和‘豫西朱砂’中均高表达,推测这3个基因在‘治章骨红重翠’木质部红色成色中起到重要作用。具有红色木质的‘豫西朱砂’和‘治章骨红重翠’在CHSCHIANSUFGT基因上相对高表达,这可能与其红色木质的产生密切相关。本次试验结果中‘豫西变绿萼’的CHS相对表达量高于‘豫西朱砂’,张启翔等在对梅花木质进行转录组分析时发现,朱砂品种‘乌羽玉’的CHS表达量不及绿萼品种‘飞绿萼’,这与本次试验结果一致[13]

综合花瓣、萼片和木质部实时荧光定量PCR结果,MYBɑ1MYB1bHLH3是影响这3个品种花部与木质部呈现红色的重要转录因子基因,这些转录因子的表达促进矢车菊通路下游的结构基因ANSUFGT高表达,从而促进了红色花色苷的产生。

2.4 ‘治章骨红重翠’梅跨品种群特性分析

结合表型、花色苷含量及实时荧光定量PCR测定结果推测,‘治章骨红重翠’在花瓣上与‘豫西变绿萼’有相似的表达机制——矢车菊合成通路上其他分支基因FLSF3′5′HLARANR高表达(图 2),共同竞争花色苷合成底物,形成了大量的无色原花青素与类黄酮,且GST基因低表达而无法将花色苷前体转运到液泡实现最终呈色,从而表现为偏白色的花瓣。‘治章骨红重翠’在萼片上与‘豫西变绿萼’有相似的表达机制——表现为整个花色苷通路上的低表达或表达受阻,F3′HDFRANS基因相对低表达,这些低表达的基因使得红色花色苷合成受限,从而表现为绿色萼片。‘治章骨红重翠’在木质部上与‘豫西朱砂’存在相似的表达机制——MYBɑ1MYB1bHLH3基因高表达,正向调控花青素合成通路下游结构基因ANSUFGT高表达,促进红色花色苷的产生,从而表现为红色木质(图 9)。‘治章骨红重翠’花瓣与萼片在花色苷含量上存在一定程度正相关性,但在花色苷表达模式上有所不同;花瓣与木质部在花色苷含量与花色苷表达模式上均显著不同。

图 9 三个品种的花瓣、萼片和木质部颜色形成机制推测[13] Fig. 9 Inference of color-forming mechanisms for petals, sepals and xylem of three cultivars[13]. LE: 'Yuxi Bian Lü'e'; CCGH: 'Zhizhang Guhong Chongcui'; ZS: 'Yuxi Zhusha'. The solid black arrow indicates direct control. The dashed arrow indicates indirect regulation. LE:‘豫西变绿萼’;CCGH:‘治章骨红重翠’;ZS:‘豫西朱砂’
3 讨论与结论

对于植物各部位颜色的成因的探究一直是园林植物研究的热点,以往的研究主要集中于果皮、叶片和花瓣,对于木本植物花部与木质部颜色的探究较少[19-23]。在梅花中,朱砂品种群和绿萼品种群一直备受关注[13, 24-28]。本研究从一个具有跨品种群特性的梅花新品种‘治章骨红重翠’出发开展试验,因其同时具有朱砂品种群和绿萼品种群的典型特征,在对花部与木质部颜色的探究上可作为突破口。试验以实时荧光定量PCR结合颜色表型与生理指标对其花瓣、萼片和木质部颜色成因进行了初步剖析,探究产生该现象的分子机制。

‘豫西变绿萼’萼片中的花青素合成通路基因高表达,这与其花瓣中的表现相似。张启翔等发现绿萼品种‘飞绿萼’在CHSFLS基因上高表达,认为其促进了其他无色类黄酮的产生,且发现梅花木质部大量积累原花青素[13]。赵昶灵等发现梅花花色差异与总黄酮含量间似乎无明显规律性[15]。据此推测,‘豫西变绿萼’的F3′5′H等基因具有较高表达水平,其与F3′HF3H共同竞争底物,而后在LARANR等的催化下,产生了更多的无色类黄酮类物质(图 2)。共同竞争底物这一点可以解释为何‘豫西变绿萼’木质部仍能检测出少量的总花色苷。有研究指出GST对于花青素的运输起到了重要作用[5-6],花青素需要转运到液泡中实现储存及最终颜色呈现,GST在朱砂品种中表达,而在绿萼品种中不表达[13],这可能解释了绿萼品种木质部未能呈现红色的原因。

前人开展过月季的花色与花香关联性分析[29],王秀军等在研究梅花的花香机制时,发现PALMYB44CL参与了梅花花香的形成[30],这些基因多位于花青素合成通路的上游,本研究发现绿萼品种花青素合成通路上游基因高表达,而绿萼品种一般花香较为浓郁,其花香与花色在合成机制上是否有关联?其原因值得深入发掘。

总花色苷含量是花瓣颜色差异的主要原因[15]。前人在研究海棠叶色时认为叶绿素主要决定了海棠叶片色彩的基调,而花青素与类胡萝卜素含量增加了叶片色彩的多样性[31-32]。3个品种的萼片中均有一定量的花色苷产生,萼片颜色差异原因可能与总花色苷含量和叶绿素含量的比例有关,高含量的花色苷使得朱砂品种萼片呈现绛紫色,而低浓度时,‘治章骨红重翠’与‘豫西朱砂’的萼片呈现出绿色。木质部红色的呈现取决于总花色苷含量,多年生枝条枝内木质部红色程度一般大于一年生枝条,这与色差仪的测量结果一致。

在梅花现存的品种中存在一个“绿萼朱砂”品种类群:‘单瓣绿萼朱砂’ ‘复翠骨红’ ‘治章骨红重翠’和‘重翠粉朱砂’等,跨度从单瓣、复瓣、重瓣,延伸至台阁。从性状记录上看,均具有如下几个特征:木质部淡暗紫色、萼片淡绿色、花瓣初开时略带肉粉色,盛开时偏白色。本研究针对‘治章骨红重翠’梅开展试验,初步阐明了该类群的分类地位及共同特性形成机制,为跨品种群类群的分类提供了分子层面的依据。

本研究初步解释了‘治章骨红重翠’梅跨品种群特性成因,初步验证了影响其花瓣、萼片和枝内新生木质部颜色形成的关键结构基因与转录因子基因,对其颜色成因作出了分子层面的解析,对其跨品种群特性作出了初步解释,为梅花花色与木质部颜色的分子育种提供了参考。

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