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林木种质资源是育种工作的重要物质基础,是决定育种效果的关键,世界各国都非常关注对种质资源的调查、搜集、评价、保存和利用[1-2]。但是,随着林木种质资源收集、保存数量的不断增加,给保存、评价和利用带来了巨大困难。Frankel等[3]在种质资源库的基础上提出了核心种质的概念,其目的是以最少数量的种质资源最大限度地保存整个群体的遗传多样性,从而解决种质资源规模过大难以管理和利用的难题。核心种质的提出为种质资源的有效保护与深入研究、利用开辟了新的途径,目前已有大量的植物构建了核心种质,但主要以作物为主[2]。相较于农作物,林木核心种质的构建起步较晚,涉及的树种也有限,近10年国内相关研究主要涉及的树种有核桃[4]、毛白杨[5]、木荷[2]、马尾松[6]等。目前构建核心种质主要是基于形态和分子标记两类数据,对于多年生、树体高大的木本植物,表型数据获取需要较长的年限;而以DNA多态性为基础的分子标记不受植物生长期影响,较形态标记更适合林木核心种质构建[7]。例如在SSR标记遗传多样性基础上,采用逐步聚类法以17.2%的入选率构建了包含164份种质的三叶木通核心种质[8];根据以等位基因最大化为标准,从272份金缕梅种质资源中提取了51份核心种质,能够代表原种质95%的等位基因数。总的来说,核心种质是种质资源的重复子集,有助于资源长期保存和长效利用,可以帮助研究者快速捕捉到具有目标性状的种质,提高育种效率[9]。
楠木(Phoebe zhennan)是我国特有的珍贵用材树种,其优质大径级木材因呈现金黄色绢丝状而被称为“金丝楠”,是“金丝楠木”的最优来源树种之一,但由于其生长缓慢,加之历代无节制采伐,楠木资源趋于枯竭,楠木现存资源多为人工栽培群体[10-11]。人为活动的干扰可能会导致降低其遗传多样性水平,大量优良基因缺失,群体趋于纯化,遗传基础变窄[12]。而珍贵用材是林木资源战略储备的重要组成部分,因此,加强对珍贵树种楠木的恢复性培育尤为重要,并应作为长期坚持的任务。为了保护楠木的优良种质资源和维持其可持续性遗传改良,亟需开展楠木核心种质的构建。鉴于此,我们以楠木第一轮育种群体(102份种质资源)为研究对象,利用SSR引物进行基因分型,通过比较和分析不同抽样策略下构建的核心种质遗传参数评价,确定楠木核心种质构建的最适取样策略和比例,期望用最少的种质最大程度保存楠木遗传多样性,同时为楠木种质资源的深入研究和加强利用、发掘优异基因资源提供理论依据和核心材料。
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2012年,在四川、重庆、湖南、湖北和贵州省等楠木产区根据树高、胸径和环境适应性选择优树102株,基本涵盖了楠木天然分布区,分单株采集优树种子,沙藏;2013年春季分家系育苗;2014年在泸州市玉蟾山国家林草长期科研基地建立楠木种质资源基因库(105.387529°E, 29.137715°N, 海拔553 m)。2022年6月,对102个家系采集新鲜嫩叶,将其放入硅胶中保存,带回实验室置于−80℃冰箱中保存备用。
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本研究采用改良CTAB法快速提取楠木基因组DNA。选用14对条带清晰、多态性强的SSR引物进行PCR扩增(见表1),SSR引物由生工生物(上海)股份有限公司合成荧光引物,扩增产物经Fragment Analyzer全自动毛细管电泳分析仪进行检测[13]。
引物编号
Marker重复基序
Repeat motif引物组合
Primer pair (5'-3')预期产物大小
Predicted size (bp)MN-g30 (GA)30 AGAGATGTACCTCGCTGCGT 156 GAGAGCCCATCATGACCAAT ZiN-e8 (TAACAG)4 CCTTTAACAACATCAAAACCATC 239 ATCAAGTTAACAGAATTCGCAAG MN-e96 (TAAA)5 TGGGTTTAGCCGTCACTACC 107 TCACTGCCTTGGCTCTGTAA MN-g3 (TC)34 TTGAGGGGGAATGTTGAGAG 248 TGAAGGCAACTGATCACAAGA MN-g5 (GA)35 AAATGGTTGGGTCAAGTTCG 325 GTGCCCATATACCCGATGAC MN-g18 (TC)30 GAAGGTCCTCCTATCCTGCC 153 AATCCGGCTGATACTTCTGC Unigene29601 - GCAGGTATCTGTTGTGTCTTC 287 CATTCGTCTTCTTGGAGTCATC CL20730Contig1 - CCACTGCCACTGCCACTG 255 GCCTCCCTCAACTCCATTCC CL4747Contig1 - ACATCAGAGGCAGGCAGG 287 CGGAGGCGGCAAGATTTG PZmf02 (AT)5 CTCCTGCAAAGAAAGGGGGT 224 ACAGATTGTGGCACTACCCG PZmk03 (TA)5 GGTTTTCAAGACCGGGGCTA 216 CATGGAGTCCGGGGAAATCC PZmf07 (TC)5 CGGATCAGATAGAGTCGGCG 268 TCATCCAACAGGAATAGTTGTTCT PZmf05 (TA)7 CGACCCGCGAAAAGATATACTC 238 AGCTCGCCATTCCATAAGCT PZmf06 (TC)6 TAATATAATAGAGCCAAAGAGGAGGT 201 AACAATAATCCTCTATCCGGATCT Table 1. Base information of SSR primers used in core collection construction of Phoebe zhennan
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(1)M策略:以核心种质中标记位点最大化为标准的核心种质构建方法[14]。通过Core Finder软件以等位基因最大化为原则抽取核心种质[15]。
(2)随机取样法:依据张春雨等[16]随机取样策略,以10%、20%、40%和50%为取样比例,分别构建核心种质。
(3)以核心种质保留等位基因或遗传多样性最大化分别构建核心种质,抽样比例为10%、20%、40%和50%,借助PowerMarker version 3.25软件进行核心种质的抽取[17]。
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使用Genemarker 2.2.0软件分析毛细管电泳数据。Cervus 3.0.7软件计算多态信息含量(PIC)[18]。利用GeneAlEx 6.5软件[19]计算等位基因数、有效等位基因数、期望杂合度、观测杂合度及Shannon’s信息指数,用这些指标来评价核心种质、原有种质与保留种质的遗传多样性,并通过t检验对核心种质与原有种质各遗传多样性指标进行差异显著性分析[2]。同时,运用主坐标分析法对构建的核心种质进行确认。最后,将SSR-PCR产物毛细管电泳谱带转化为数字指纹图谱,以此构建楠木核心种质的分子身份信息。
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利用14对SSR引物对102份楠木种质资源进行遗传多样性分析(见表2)。结果显示,14对SSR引物共检测到166个等位基因,每对SSR引物检测到等位基因数的范围在2(PZmf07、CL20730Contig1、PZmf05和PZmf02)~37(MN-g3)之间,平均为12。有效等位基因数平均为4.875,各引物检测到的有效等位基因数在1.021(PZmf02)~3.125(MN-g3)之间。期望杂合度与观测杂合度分别在0.117(PZmf07)~0.943(MN-g3)和0.000(PZmf07、PZmf05、PZmf06和PZmf02)~0.978(MN-g3)之间,平均分别为0.561和0.373。Shannon’s信息指数最高的为引物MN-g3(3.125),其次为引物MN-g5(3.029),最低为引物PZmf02(0.057),楠木种质资源平均Shannon’s信息指数为1.297。以上结果表明楠木种质资源具有较为丰富的遗传多样性。
位点
Locus等位基因数
Na有效等位基因数Ne Shannon’s信息指数I 观测杂合度Ho 期望杂合度He 多态信息指数
PICPZmk03 4 1.991 0.739 0.022 0.500 0.384 ZiN-e8 10 1.476 0.761 0.048 0.325 0.306 Unigene29601 8 2.894 1.354 0.228 0.658 0.617 MN-g30 33 11.276 2.885 1.000 0.916 0.906 PZmf07 2 1.131 0.232 0.000 0.117 0.109 MN-e96 5 2.373 0.995 0.924 0.582 0.491 PZmf05 2 1.707 0.605 0.000 0.416 0.328 PZmf06 3 1.632 0.612 0.000 0.389 0.320 CL20730Contig1 2 1.160 0.265 0.149 0.139 0.128 MN-g3 37 16.015 3.125 0.978 0.943 0.934 MN-g5 34 14.387 3.029 0.278 0.936 0.926 MN-g18 18 9.034 2.530 0.937 0.894 0.881 CL4747Contig1 6 2.150 0.969 0.653 0.538 0.459 PZmf02 2 1.021 0.057 0.000 0.502 0.375 平均Mean 12 4.875 1.297 0.373 0.561 0.512 Na: Number of different alleles, Ne: Number of effective alleles, I: Shannon’s information index, Ho: Observed heterozygosity, He: Expected heterozygosity, PIC: Polymorphic information content Table 2. The genetic diversity parameters of P. zhennan germplasm resources
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随取样比例的增加,不同取样策略构建的候选核心种质等位基因数及其保留率呈逐渐上升的趋势(见表3)。在取样比例较低时,各遗传多样性参数值和保留率均处于较低水平。如随机取样和遗传多样性最大化策略在取样比例低于20%时,其等位基因数和有效等位基因数的保留率均低于60%,表现出明显的等位基因缺失。当取样比例为50%时,虽然随机取样、等位基因最大化和遗传多样性最大化法构建的候选核心种质Shannon’s信息指数均略高于原有种质,但其余遗传多样性参数,如观测杂合度、期望杂合度明显低于原有种质。而M策略以58.8%的取样比例构建的核心种质有效等位基因数、Shannon’s信息指数、观测杂合度以及期望杂合度均明显高于原有种质,等位基因数保留率100%。不同取样策略构建的候选核心种质与原有种质遗传参数t检验结果显示,Shannon’s信息指数和期望杂合度在各种质间无显著差异,候选核心种质与原有种质存在显著差异的遗传参数主要集中在等位基因数、有效等位基因数和观测杂合度。10%取样比例时,随机取样、等位基因最大化和遗传多样性最大化法构建的候选核心种质等位基因数和有效等位基因数均显著低于原有种质。M策略构建的核心种质各遗传参数与原有种质并无显著差异。根据5个遗传参数的综合考虑,选择M策略抽取的60份(58.8%)种质资源构建的楠木和新种指能够以较小的种质份数最大程度地代表整个楠木种质资源地遗传多样性。利用M策略构建的楠木核心种质中包含四川36份(55.4%)、湖北5份(45.5%)、湖南11份(64.7%)、贵州5份(83.3%)和重庆3份(100.0%)共计60份种质材料。
取样策略
Sampling strategy种质数
Number平均等位基因数
Mean Na平均有效等位基因数
Mean Ne平均Shannon's信息指数
Mean I value平均期望杂合度
Mean He平均观测杂合度
Mean Ho原有种质 102 12 4.875 1.297 0.373 0.524 M策略 60 12 (100.00) 5.875 (120.51) 1.386 (106.86) 0.383 (102.68) 0.553 (105.53) 随机取样(10%) 10 7 (58.33)* 2.123 (43.55)* 1.034 (79.72) 0.305 (81.77) 0.318 (60.69)* 随机取样(20%) 20 7 (58.33)* 3.32 (68.1)* 1.145 (88.28) 0.311 (83.38) 0.332 (63.36)* 随机取样(40%) 41 9 (75) 4.523 (92.78) 1.246 (96.07) 0.315 (84.45) 0.347 (66.22)* 随机取样(50%) 51 10 (83.33) 4.889 (100.29) 1.345 (103.7) 0.335 (89.81) 0.359 (68.51)* 等位基因最大化(10%) 10 8 (66.67)* 2.234 (45.83)* 1.193 (91.98) 0.354 (94.91) 0.339 (64.69)* 等位基因最大化(20%) 20 10 (83.33) 3.1134 (63.86)* 1.242 (95.76) 0.362 (97.05) 0.346 (66.03)* 等位基因最大化(40%) 41 11 (91.67) 5.235 (107.38) 1.328 (102.39) 0.373 (100.00) 0.362 (69.08) 等位基因最大化(50%) 51 12 (100) 5.584 (114.54) 1.332 (102.7) 0.377 (101.07) 0.374 (71.37) 遗传多样性最大化(10%) 10 7 (58.33)* 2.119 (43.47)* 1.104 (85.12) 0.336 (90.08) 0.351 (66.98)* 遗传多样性最大化(20%) 20 8 (66.67)* 3.416 (70.07) 1.245 (95.99) 0.371 (99.46) 0.364 (69.47) 遗传多样性最大化(40%) 41 11 (91.67) 4.582 (93.99) 1.375 (106.01) 0.376 (100.8) 3.371 (70.80) 遗传多样性最大化(50%) 51 11 (91.67) 4.956 (101.66) 1.384 (106.71) 0.381 (102.14) 0.375 (71.56) 注:括号内数字为保留率/%,*表示在α=0.05水平下候选核心种质与原有种质间各项指标的统计检验具有显著差异。
Na: Number of different alleles, Ne: Number of effective alleles, I: Shannon’s information index, Ho: Observed heterozygosity, He: Expected heterozygosityTable 3. Comparisons of genetic diversity parameters of candidates core collection constructed by different tactics
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M策略构建的楠木核心种质保留了原有种质58.8%的材料,等位基因数、有效等位基因数、Shannon’s信息指数、观测杂合度和期望杂合度的保留率分别为100.0%、106.9%、105.5%和102.7%(见表4)。t检验结果也表明,利用M策略构建的楠木核心种质和原有种质的遗传多样性参数间差异不显著。由此,认为本研究利用M策略构建的核心种质具有很高的代表性。采用主坐标分析法(PCoA)对构建的核心种质进行比较分析,以进一步确定其代表性。结果显示,楠木核心种质在整个种质资源的主坐标图内均匀分布,表明M策略构建的楠木核心种质具有很好的代表性(见图1)。
种质 种质数 Na Ne I He Ho 原有种质 102 166 68.247 1.297 0.373 0.524 核心种质 60 166 (58.8) 69.534 (100.0) 1.386 (106.9) 0.383 (102.7) 0.553 (105.5) 保留种质 42 125 (41.2) 62.495 (91.6) 1.134 (87.4) 0.328 (87.9) 0.447 (85.3) 注:括号内数字为保留率/%。
Na: Number of different alleles, Ne: Number of effective alleles, I: Shannon’s information index, Ho: Observed heterozygosity, He: Expected heterozygosityTable 4. Comparison of genetic diversity parameters among core collection, reserve collection, and original collection
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利用14对SSR引物扩增的全部多态性谱带构建了60份楠木核心种质的分子身份信息(见表5)。每份核心种质材料都有其唯一的分子身份信息,可以通过其专一的分子身份信息将60份核心种质材料相互区分鉴别出来。
核心种质
Core collection分子身份信息
Molecular ID核心种质
Core collection分子身份信息
Molecular IDZNcq01 DDFFIUADAAOgMMFLDEBBBBA ZNsc20 GGBFNaDD00Sdc000BEABBA ZNcq02 CCEEIOADAATfYYCPDEBAABA ZNsc21 CCBFVcADAAdiaaIIEEAAACA ZNcq03 DDFFJVADAA00OOFLDEBBABA ZNsc22 DDDDLVADAANaBHCE00ABACA ZNgz01 DDBBPWADAANdBDGHDEABABA ZNsc24 IIDDLVAD00MYBGCEBEBACA ZNgz02 DDEEIRADAASbUUCPDEBBABA ZNsc27 BDEEIRADAAQZVVCPDEABABA ZNgz03 DDCHGKADABCITVCCEEABACA ZNsc28 EE00ISADAAScVVCPDEBBBBA ZNgz05 DDFFIRADAA0000CP00BBABA ZNsc29 DDCCIYADABMcBBGJEEABBBA ZNgz06 DDFFIRADAASbUUCPDEBBABA ZNsc31 CCACIXADAAMcBBGJEEABBBA ZNhb01 00FFKOADAASfXXCODEBBBB ZNsc32 DDBBFQADABJWPPKKEEBAACA ZNhb03 DDFFMN00AA00WWCODEBBABA ZNsc33 DDFFIRADAAWfXXCPDEBBABA ZNhb07 00FFIRADAARZUUCQDEABABA ZNsc34 DDFFBTADAAFK00KK00BBACB ZNhb10 DDFFIRADAASbUUCPDEABAB ZNsc35 00CFNaDDAASeeeIMEEABBBA ZNhb11 DDFFHXADAAUUBIMMEEBBBCA ZNsc37 DDCFNZADABSeddIMEEABBBA ZNhn01 DDFFIRADAASbUUCPDEBBBBA ZNsc38 CCCFOaDDAASeeeIMEEABBBA ZNhn02 DD00IRADAASbVVCPDEBBBBA ZNsc39 CC00S0ADAAAeTTBGEEBBBBA ZNhn03 DDCFNaADAASeffIMEEABBBA ZNsc41 DDCCKVADABCMFTCHEEABACA ZNhn04 DDFFR0ADAAQaLTBKDDBBBCA ZNsc43 DDFGSVADABBeTTBGEEBBBBA ZNhn05 DDFFIRADAAQcXXCPDEBBBBA ZNsc46 DDFFJWADABScMMFLDEBBBBA ZNhn08 DH00RSAD00PZKSBKBDBACA ZNsc47 DDBEC0ADAAHHggLLFFABBCA ZNhn09 DDFFJOADAAdfWWCQDEBBABA ZNsc48 DDBBIXADABLbBBGJEEABABA ZNhn10 DDFFOgBDAACHRRHRDDBBACA ZNsc49 DDBFAfBDABEYEQCKEEBBBCA ZNhn11 00FFKOBDAASfWWCODEBBABA ZNsc50 DDCCIWADAAMcBBGJEEABBBA ZNhn13 BJFFKOADAASfXXCODEABABA ZNsc52 FFCFAfBD00DXEQCKBEBBCA ZNhn14 00000000AA00000000BAAA ZNsc53 00CFAfAD00DW00CKAEAACA ZNsc02 ADDFVbADAAGWKiHJEEABBCA ZNsc54 DDCCDSADAAUWFNDNDFABABA ZNsc05 DDFFVdADAAGWKhHJEEABACA ZNsc55 CCCFScCDAAAYCiBIEEBBBCA ZNsc09 DDBFHV00AAMfAFGLEFBBACA ZNsc58 DDBESeCDABBYCiBIEEBBACA ZNsc11 DDBBchBBAAbjJbARCEBBABA ZNsc60 DDCCESADABUWENDNDFABBBA ZNsc14 CCBBahBBAAdjJbARCEBBABA ZNsc61 DDEEIPBDAAVdWWCPDEBBACA ZNsc19 000000BEAAYkDZGLDDABA ZNsc62 00FFJVADAASdQQFLDEBAABA 注:表中大写和小写字母表示SSR引物迁移谱带顺序,根据谱带从大到小依次为A, B, C…或a, b, c…,00表示无扩增条带。 Table 5. Molecular ID of core collection
Construction of Core Collection of Phoebe zhennan Based on SSR Molecular Markers
doi: 10.12172/202305190001
- Received Date: 2023-05-19
- Available Online: 2023-05-30
- Publish Date: 2023-08-30
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Key words:
- Phoebe zhennan /
- SSR /
- Core collection /
- Molecular ID
Abstract: Phoebe zhennan is a precious and unique timber species in China. The establishment of a core collection have important value for the strengthen of resources protection and utilization, and speed up the breeding process of P. zhennan. Taking 102 germplasms of P. zhennan as materials. The methods of maximization strategy (M strategy), random sampling, simulated annealing algorithm maximizing the genetic diversity, and simulated annealing algorithm maximizing the number of alleles were used to construct the core collections using 14 SSR primers. The results showed that 166 alleles were detected by 14 SSR primers, and the average of the effective alleles was 4.875. The Shannon’s information index was 1.297, indicated relative high genetic diversity in the germplasms of P. zhennan. Comparative analysis showed that the core collections with relative high sampling proportion of constructed by maximization strategy, simulated annealing algorithm maximizing the genetic diversity, and simulated annealing algorithm maximizing the number of alleles were all showed high representativeness. The retention of alleles in core collections that constructed by simulated annealing algorithm maximizing the number of alleles and maximization strategy were all reached 100.00%, but the retention of the effective alleles and genetic diversity in core collection that constructed by algorithm maximizing the number of alleles were lower than maximization strategy. There was no obviously difference of the retention of Shannon’s information index in core collections that constructed by simulated annealing algorithm maximizing the genetic diversity and maximization strategy, but the alleles and effective alleles in core collection that constructed by maximization strategy were higher than simulated annealing algorithm maximizing the genetic diversity. Therefore, maximization strategy was the best sampling strategy in core collection construction according to the genetic diversity parameters. The principal coordinate analysis also showed that the core collection could represent the genetic diversity of the origin collection. The 60 germplasms includes 58.8% of the all germplasms, the retention of alleles, effective alleles, and Shannon’s information index were 100.00%, 120.51%, and 106.86%. Specific molecular identity for 60 core collections were established by the bands of 14 SSR primers, which could accurately identification the core collections. Our results provided theoretical basis and core materials for further research, utilization, and excellent gene resource mining of P. zhennan germplasms.