小麦族猬草属和赖草属植物的系统发育研究
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摘要
小麦族(Triticeae)是禾本科(Poaceae)中一个十分重要的类群,约有28属380余种。小麦族内大多数物种为草原和草甸的主要组成成分,许多种类是优良的牧草,具有较高的饲用价值,也是现代麦类作物改良和牧草遗传育种的重要基因资源。因此,对小麦族植物进行正确分类,研究各类群间的亲缘关系和系统进化历史,在理论和实践上有重要意义。
猬草属(Hystrix Moench)由Moench(1794)根据其颖强烈退化甚至缺失的特点而建立,模式种为Hy. patula Moench。自建属以来,猬草属的分类地位和界限、物种的染色体组组成等一直处于争论之中。Dewey(1982,1984)基于染色体组分析,认为模式种Hy. patula含有StH染色体组,因此将猬草属物种合并到含StH染色体组的披碱草属(Elymus)中。Jessen&Wang(1997)通过染色体组分析以及基因组特异RAPD标记认为Hy. coreana和Hy. californica具有赖草属(Leymus Hochst.)的NsXm染色体组,将Hy.coreana组合到赖草属中。Zhang et al.(2006)基于染色体组分析和基因组原位杂交分析认为Hy. patula含有StH染色体组,Hy. duthiei和Hy. duthiei ssp. longearistata含Ns染色体组,与赖草属物种亲缘关系密切。Ellneskog-Staam et al.(2007)根据基因组原位杂交和Southen杂交的结果显示：分布于中国东北的Hy. komarovii具有与Hy. patula相似的StH染色体组,而猬草属其余物种(Hy. duthiei、Hy. duthiei ssp. longearistata和Hy. coreana)的两个染色体组为Ns1Ns2。因此目前关于猬草属的系统学问题主要是猬草属是否是一有效的属,该属物种的染色体组组成以及与近缘属物种的关系如何,一直是争议的焦点。
本研究从微形态结构(表皮微形态特征和解剖结构)、细胞学(染色体组分析、基因组原位杂交)和分子系统学(叶绿体atpB-rbcL基因间隔区、低拷贝核RPB2基因、多拷贝核ITS序列)三个方面对猬草属和赖草属物种进行系统学研究,重点探讨猬草属的系统地位、猬草属和赖草属植物的染色体组组成、可能的二倍体属供体、以及属(种)间的系统关系。主要结果如下：
1、基于叶绿体基因间隔区atpB-rbcL序列对猬草属、赖草属和近缘属物种的系统发育分析显示：(1)猬草属模式种Hy. patula与拟鹅观草属和披碱草属物种聚为一支,表明Hy. patula与披碱草属植物亲缘关系近,其母本来源为含St染色体组的拟鹅观草属物种；(2) Hy. duthiei、Hy. duthiei ssp. longearistata、4个新麦草属物种及L. mollis和所有欧亚分布的赖草属物种聚在一支,说明Hy. duthiei、Hy. duthiei ssp. longearistata与欧亚赖草亲缘关系较近,其母本供体来自含Ns染色体组的新麦草属物种；(3)Hy. coreana和Hy.komarovii与北美赖草及冰草属、旱麦草属、大麦属物种处于同一分支,表明Hy. coreana和Hy. komarovii与北美赖草具有较近亲缘关系,其母本供体为未知来源的Xm染色体组。
2、对猬草属、赖草属及近缘属物种的低拷贝核基因RPB2的分子序列和系统发育进行分析,结果表明：(1)异源多倍体物种中Ns拷贝的RPB2序列的核苷酸多态性明显高于其二倍体供体物种的序列多态性,中性检测Tajima's D值和Fu and Li'F值均呈显著负值,暗示NsXm染色体组物种多倍化后发生了明显的种群扩张和遗传分化；(2)RPB2基因在Hy. coreana、Hy. duthiei、Hy. duthiei ssp. longearistata、L. karelinii、L. innovatus、 L. paboauns、L. salinus、L. shanxiens和L. mollis中表现为多个拷贝序列,并且有7个来自Hy. coreana、Hy. duthiei、L. salinus、L. karelinii的RPB2序列为重组(嵌合)序列,推测重组序列来源于种间杂交和基因重组；(3)猬草属模式种Hy. patula含有StH染色体组,与披碱草属、拟鹅观草属和大麦属具有较近的亲缘关系；猬草属的其它物种Hy.duthiei、Hy. duthiei ssp. longearistata、Hy. coreana和Hy. komarovii含有NsXm染色体组,与新麦草属和赖草属植物亲缘关系密切；(4)H染色体组可能以基因渗入的方式参与Xm染色体组的组成；(5)L. molli与中亚赖草L. multicaulis关系密切,北美分布的L. mollis可能是由中亚分布的物种迁徙而至,并且与StH染色体组物种发生过遗传交流。
3、对含NsXm染色体组组成的猬草属、赖草属及近缘二倍体属物种的ITS序列进行序列特征分析,构建ITS系统发育树。结果表明：(1)猬草属物种的ITS序列与赖草属和新麦草属聚类,表明Hy. coreana、Hy. duthiei、Hy. duthiei ssp. longearistata和Hy. komarovii与赖草属植物亲缘关系较近；(2)猬草属和赖草属物种中Ns-染色体组类型的ITS序列来源于新麦草属,P/F和St染色体组类型的ITS序列分别来源于AgropyronlEremopyrum和Pseudoroegneria物种；(3)ITS序列呈现出单亲类型(Ns染色体组类型)占优势,推测与赖草属的部分异源多倍体起源有关；(4)猬草属和赖草属物种的Ns类型的ITS序列聚类呈明显的地理分布特征,显示猬草属和赖草属物种的ITS谱系结构与物种的地理分布存在关联,推测不同生态和地理环境下的自然选择导致物种的适应分化和物种形成,并且也引起rDNA基因的进化分歧。
4、对猬草属和赖草属物种进行了属(种)间人工杂交及细胞遗传学观察。杂交结果如下：(1)共计进行了23组种间及属间杂交组合,获得13个组合的杂种植株；(2)以Hy.duthiei和Hy. duthiei ssp. longearistata为母本与Hy. coreana及赖草属物种的授粉率较高,杂交后种子发育初期结实率可达38%,但是种子发育后期衰退,导致形成干瘪种子,可能与某些影响胚乳发育的基因有关；(3)赖草属种间杂交结实率较高,容易获得杂种植株。对杂种F1减数分裂中期Ⅰ花粉母细胞的染色体配对情况进行了观察和统计,结果显示：L.multicaulis x L. crassiusculus平均每细胞形成12.87个二价体,L. qinghaicus x L. multicaulis和L. multicaulis x L. qinghaicus平均每细胞分别形成12.07和11.92个二价体,表明L.crassiusculus和L. qinghaicus具有与L. multicaulis相同的染色体组组成,即NsXm染色体组,作为赖草属中的新分类群是恰当的。
5、对3个猬草属物种(Hy. komarovii、Hy. core ana和Hy. duthiei ssp. longearistata)和4个赖草属物种(L.flexus、L. mundus、L. racemosus和L. secalinus)进行单色基因组原位杂交(GISH)分析。结果表明：(1) Hy. komarovii的染色体组中不含St染色体组和H染色体组；(2) Hy. komarovii、Hy. coreana和Hy. duthiei ssp. longearistata与供试的4个赖草属物种的染色体组成相似,很可能为两个来源于新麦草属的Ns染色体组,或Xm染色体组与Ns染色体组高度同源；(3)Ee染色体组与NsXm染色体组有一定的同源性,导致一些高度重复的小片段杂交；(4)Xm染色体组并非来自P染色体组。
6、对猬草属和赖草属以及近缘属披碱草属植物的叶表皮微形态和叶片横切面解剖结构进行了观察。结果显示：(1)叶表皮形态与解剖结构都具有种内稳定性和种间差异性,具有物种鉴分的参考价值,但在属间或属内分组水平上的分类意义不大；(2)在叶表皮微形态上长细胞的壁形态、短细胞的有无、气孔的密度等性状差异明显；(3)解剖结构上,中肋的存在与否及形态、中央维管束的分布位置等性状具有较高的区分价值；(4)叶表皮形态与解剖结构特征表现出与植物所生长的生态环境的适应性。
The tribe Triticeae, which includs about28genus and380species, is an enormous important group in Poaceae. Many of species in Triticeae are important cereal and forage grasses, which are precious germplasm resources in crop improvement and forage breeding. So, it is important to study the genetic and phylogenetic relationships among Triticeae species before we use the Triticeae germplasms.
Hystrix Moench is a small perennial genus of the tribe Triticeae. According to the distinct morphological character of highly reduced glumes or long setaceous awn-shaped ones, if present, it was established by Moench (1794). The type species is Hystrix patula Moench. Dewey (1982,1984) reported that Hy. patula contains the StH genome, and combined the species of Hystrix into Elymus. Several studies have suggested that the genomes of the other species of Hystrix are different from the StH genome of Hy. patula (Jensen&Wang1997; Svitashev et al.1998; Muramatsu2001; Zhang et al.2002; Zhang and Zhou2006; Zhang et al.2006). Jensen&Wang (1997) proposed that Hy. coreana and Hy. californica had the same genome constitution NsXm as Leymus Hochst., and combined these two species into Leymus. The chromosome pairing and genomeinsitu hybridization (GISH) analyses indicated that Hy. coreana, Hy. duthiei and Hy. duthiei ssp. longearistata shared the NsXm genomes of Leymus, and should be treated as species of Leymus (Zhang et al.2006; Zhang&Zhou2006). Based on the Southen and GISH analysis, Ellneskog-Staam et al.(2007) advocated that Hy. komarovii most likely had a variant of the StH genome of Hy. patula, and should be transferred to the genus Elymus. It was also considered that Hy. coreana, Hy duthiei and Hy. duthiei ssp. longearistata had the Ns'Ns2genome constitutions (Ellneskog-Staam et al.2007). Therefore, the definition of Hystrix and its precise taxonomic status are still under discussion today. Some authors included the species in either Hystrix (Sakamoto1973; Kuo1987; Osada1993; Baden et al1997; Zhou et al.2000) or Asperella (Keng1959; Baum1983; Ohwi1984; Koyama1987), while others regarded it as a part of Elymus (Dewey1982; Love1984) or Leymus (Jensen&Wang1997; Zhang et al.2006). Now the disputes about Hystrix are:whether it is a valid genus? What are the genome constitutions of Hystix species? How about the phylogenotic relationships between Hystrix and its related species?
In order to inspect the genomic constitution of Hystrix species and their precise taxonomic status, and relationship between Hystrix and Leymus, the leaf epidermal micromorphology, lamina anatomy, interspecific hybridization, chromosome pairing behavior at MI, genomic in situ hybridization (GISH), molecular phylogenetic analysis from chloroplast atpB-rbcL, nuclear RPB2and ITS sequences for Hystrix species and their related species were carried out in this study. The main results showed as follows:
1. To reveal the phylogenetic relationships and maternal donor of species in Hystrix and Leymus, the chloroplast atpB-rbcL sequences were analyzed for Hystrix and its related species. The results indicated that:(1) Hy. patula was closely related to Elymus, and the maternal donor of Hy. patula was the St genome;(2) Hy. duthiei and Hy. duthiei ssp. longearistata were closely related to the Eurasia Leymus, and the maternal donor of them were the Ns genome from Psathyrostachys;(3) Hy. coreana and Hy. komarovii were closely related to the Leymus species in North America, and their maternal donors might be the Xm genome.
2. Low copy nuclear gene RPB2was analyzed for Hystrix and its related species. The results showed:(1) Ns copy sequences of RPB2of Hystrix and Leymus have more diversity than that in Psathyrostachys, and Tajima's and Fu and Li's D values were all negative significant for RPB2gene on the Ns and Xm genome, indicated that population expansion and rapid genetic differentiation might have occurred among the species with NsXm genome in Leymus and Hystrix;(2) More than2copies of RPB2in Hy. coreana, Hy. duthiei, Hy. duthiei ssp. longearistata, L. karelinii, L. innovatus, L. paboauns, L. salinus, L. shanxiens and L. mollis were obtained, and7sequences from Hy. coreana, Hy. duthiei, L. salinus and L. karelinii were detected as recombination sequenses;(3) Hy. patula was closely related to Pseudoroegneria, Hordeum and Elymus;(4) Hy. duthiei, Hy. duthiei ssp. longearistata, Hy. coreana and Hy. komarovii contain NsXm genome, and were closely related to Psathyrostachys and Leymus;(5) H genome of Hordeum may involve in the composition of Xm genome by introgression;(6) L. mollis distributed in North America might have migrated from Central Asia, and have close relationship with L. multicaulis; L. mollis might have gene exchange with the species contained StH genome by some way.
3. Sequence and phylogenitical analysis were carried out for ITS sequence from species of Hystrix and Leymus combined with30diploid species in Triticeae. The results were:(1) abundent ITS polymorphism were detected among Hystrix and Leymus, and the pattern of rDNA variation is associated with geographic distribution pattern;(2) Ns-genomic types of Hystrix and Leymus were originated from Psathyrostachys, P/F and St genomic types of Leymus were originated from AgropyronlEremopyrum, and Pseudoroegneria species, respectively;(3) the occurrence of a higher proportion of Hystrix and Leymus species with dominant uniparental rDNA type may associated with the segmental allopolyploid origin, and adaptive radiation in Hystrix and Leymus.
4. A total of23interspecific or intergeneric cross combinations involving Hystrix and Leymus species were performed, and13hybrid F1plants were obtained. Meiosis analysis of3hybrids from species of Leymus were carried out. Meiosis analysis showed that:(1) in the tetraploid hybrids of L. multicaulis x L. crassiusculus, L. qinghaicus x L. multicaulis, and L. multicaulis x L. qinghaicus, an average of12.87,12.07and11.97bivalents per cell was observed at MI, respectively, suggesting that L. crassiusculus and L. qinghaicus share the same basic NsXm genome of L. multicaulis. Thus, it is reasonable that L. crassiusculus and L. qinghaicus were treated in Leymus.
5. Genomic in situ hybridization (GISH) analysis was carried out in three Hystrix species (Hy. komarovii, Hy. coreana and Hy. duthiei ssp. longearistatd) and4Leymus species (L. flexus, L. mundus, L. racemosus and L. secalinus). GISH analysis indicated that:(1) Hy. komarovii has the NsXm genome instead of the StH genome;(2) Hy. komarovii, Hy. coreana and Hy. duthiei ssp. longearistata have the NsXm genomeof Leymus;(3) in species of Leymus, the Xm genome is closely related to Ns genome, and the Xm genome may be another Ns genome;(4) Ee genome is homology with the NsXm genome in a lower degree;(5) Xm genome did not origin from P genome.
6. The leaf epidermal micromorphology and anatomical structure of Hystrix, Leymus and Elymus was examined under light microscope. The results showed that:(1) a number of variations of epidermal micromorphology and anatomical structure exist at the species level, and may be used for distinguishing different speicies, but not for different genera;(2) variations of epidermal features includes variation in morphology and wall thickness of long cells, morphology and distribution patterns of short cells and distribution of prickles;(3) the leaf anatomical features such as the presence or absence of keel, the outline of keel if it is present, arrangement of vascular bundles, have more distinguishing value between different species;(4) the variation of epidermal micromorphology and anatomical structure is related closely to environment.
猬草属(Hystrix Moench)由Moench(1794)根据其颖强烈退化甚至缺失的特点而建立,模式种为Hy. patula Moench。自建属以来,猬草属的分类地位和界限、物种的染色体组组成等一直处于争论之中。Dewey(1982,1984)基于染色体组分析,认为模式种Hy. patula含有StH染色体组,因此将猬草属物种合并到含StH染色体组的披碱草属(Elymus)中。Jessen&Wang(1997)通过染色体组分析以及基因组特异RAPD标记认为Hy. coreana和Hy. californica具有赖草属(Leymus Hochst.)的NsXm染色体组,将Hy.coreana组合到赖草属中。Zhang et al.(2006)基于染色体组分析和基因组原位杂交分析认为Hy. patula含有StH染色体组,Hy. duthiei和Hy. duthiei ssp. longearistata含Ns染色体组,与赖草属物种亲缘关系密切。Ellneskog-Staam et al.(2007)根据基因组原位杂交和Southen杂交的结果显示：分布于中国东北的Hy. komarovii具有与Hy. patula相似的StH染色体组,而猬草属其余物种(Hy. duthiei、Hy. duthiei ssp. longearistata和Hy. coreana)的两个染色体组为Ns1Ns2。因此目前关于猬草属的系统学问题主要是猬草属是否是一有效的属,该属物种的染色体组组成以及与近缘属物种的关系如何,一直是争议的焦点。
本研究从微形态结构(表皮微形态特征和解剖结构)、细胞学(染色体组分析、基因组原位杂交)和分子系统学(叶绿体atpB-rbcL基因间隔区、低拷贝核RPB2基因、多拷贝核ITS序列)三个方面对猬草属和赖草属物种进行系统学研究,重点探讨猬草属的系统地位、猬草属和赖草属植物的染色体组组成、可能的二倍体属供体、以及属(种)间的系统关系。主要结果如下：
1、基于叶绿体基因间隔区atpB-rbcL序列对猬草属、赖草属和近缘属物种的系统发育分析显示：(1)猬草属模式种Hy. patula与拟鹅观草属和披碱草属物种聚为一支,表明Hy. patula与披碱草属植物亲缘关系近,其母本来源为含St染色体组的拟鹅观草属物种；(2) Hy. duthiei、Hy. duthiei ssp. longearistata、4个新麦草属物种及L. mollis和所有欧亚分布的赖草属物种聚在一支,说明Hy. duthiei、Hy. duthiei ssp. longearistata与欧亚赖草亲缘关系较近,其母本供体来自含Ns染色体组的新麦草属物种；(3)Hy. coreana和Hy.komarovii与北美赖草及冰草属、旱麦草属、大麦属物种处于同一分支,表明Hy. coreana和Hy. komarovii与北美赖草具有较近亲缘关系,其母本供体为未知来源的Xm染色体组。
2、对猬草属、赖草属及近缘属物种的低拷贝核基因RPB2的分子序列和系统发育进行分析,结果表明：(1)异源多倍体物种中Ns拷贝的RPB2序列的核苷酸多态性明显高于其二倍体供体物种的序列多态性,中性检测Tajima's D值和Fu and Li'F值均呈显著负值,暗示NsXm染色体组物种多倍化后发生了明显的种群扩张和遗传分化；(2)RPB2基因在Hy. coreana、Hy. duthiei、Hy. duthiei ssp. longearistata、L. karelinii、L. innovatus、 L. paboauns、L. salinus、L. shanxiens和L. mollis中表现为多个拷贝序列,并且有7个来自Hy. coreana、Hy. duthiei、L. salinus、L. karelinii的RPB2序列为重组(嵌合)序列,推测重组序列来源于种间杂交和基因重组；(3)猬草属模式种Hy. patula含有StH染色体组,与披碱草属、拟鹅观草属和大麦属具有较近的亲缘关系；猬草属的其它物种Hy.duthiei、Hy. duthiei ssp. longearistata、Hy. coreana和Hy. komarovii含有NsXm染色体组,与新麦草属和赖草属植物亲缘关系密切；(4)H染色体组可能以基因渗入的方式参与Xm染色体组的组成；(5)L. molli与中亚赖草L. multicaulis关系密切,北美分布的L. mollis可能是由中亚分布的物种迁徙而至,并且与StH染色体组物种发生过遗传交流。
3、对含NsXm染色体组组成的猬草属、赖草属及近缘二倍体属物种的ITS序列进行序列特征分析,构建ITS系统发育树。结果表明：(1)猬草属物种的ITS序列与赖草属和新麦草属聚类,表明Hy. coreana、Hy. duthiei、Hy. duthiei ssp. longearistata和Hy. komarovii与赖草属植物亲缘关系较近；(2)猬草属和赖草属物种中Ns-染色体组类型的ITS序列来源于新麦草属,P/F和St染色体组类型的ITS序列分别来源于AgropyronlEremopyrum和Pseudoroegneria物种；(3)ITS序列呈现出单亲类型(Ns染色体组类型)占优势,推测与赖草属的部分异源多倍体起源有关；(4)猬草属和赖草属物种的Ns类型的ITS序列聚类呈明显的地理分布特征,显示猬草属和赖草属物种的ITS谱系结构与物种的地理分布存在关联,推测不同生态和地理环境下的自然选择导致物种的适应分化和物种形成,并且也引起rDNA基因的进化分歧。
4、对猬草属和赖草属物种进行了属(种)间人工杂交及细胞遗传学观察。杂交结果如下：(1)共计进行了23组种间及属间杂交组合,获得13个组合的杂种植株；(2)以Hy.duthiei和Hy. duthiei ssp. longearistata为母本与Hy. coreana及赖草属物种的授粉率较高,杂交后种子发育初期结实率可达38%,但是种子发育后期衰退,导致形成干瘪种子,可能与某些影响胚乳发育的基因有关；(3)赖草属种间杂交结实率较高,容易获得杂种植株。对杂种F1减数分裂中期Ⅰ花粉母细胞的染色体配对情况进行了观察和统计,结果显示：L.multicaulis x L. crassiusculus平均每细胞形成12.87个二价体,L. qinghaicus x L. multicaulis和L. multicaulis x L. qinghaicus平均每细胞分别形成12.07和11.92个二价体,表明L.crassiusculus和L. qinghaicus具有与L. multicaulis相同的染色体组组成,即NsXm染色体组,作为赖草属中的新分类群是恰当的。
5、对3个猬草属物种(Hy. komarovii、Hy. core ana和Hy. duthiei ssp. longearistata)和4个赖草属物种(L.flexus、L. mundus、L. racemosus和L. secalinus)进行单色基因组原位杂交(GISH)分析。结果表明：(1) Hy. komarovii的染色体组中不含St染色体组和H染色体组；(2) Hy. komarovii、Hy. coreana和Hy. duthiei ssp. longearistata与供试的4个赖草属物种的染色体组成相似,很可能为两个来源于新麦草属的Ns染色体组,或Xm染色体组与Ns染色体组高度同源；(3)Ee染色体组与NsXm染色体组有一定的同源性,导致一些高度重复的小片段杂交；(4)Xm染色体组并非来自P染色体组。
6、对猬草属和赖草属以及近缘属披碱草属植物的叶表皮微形态和叶片横切面解剖结构进行了观察。结果显示：(1)叶表皮形态与解剖结构都具有种内稳定性和种间差异性,具有物种鉴分的参考价值,但在属间或属内分组水平上的分类意义不大；(2)在叶表皮微形态上长细胞的壁形态、短细胞的有无、气孔的密度等性状差异明显；(3)解剖结构上,中肋的存在与否及形态、中央维管束的分布位置等性状具有较高的区分价值；(4)叶表皮形态与解剖结构特征表现出与植物所生长的生态环境的适应性。
The tribe Triticeae, which includs about28genus and380species, is an enormous important group in Poaceae. Many of species in Triticeae are important cereal and forage grasses, which are precious germplasm resources in crop improvement and forage breeding. So, it is important to study the genetic and phylogenetic relationships among Triticeae species before we use the Triticeae germplasms.
Hystrix Moench is a small perennial genus of the tribe Triticeae. According to the distinct morphological character of highly reduced glumes or long setaceous awn-shaped ones, if present, it was established by Moench (1794). The type species is Hystrix patula Moench. Dewey (1982,1984) reported that Hy. patula contains the StH genome, and combined the species of Hystrix into Elymus. Several studies have suggested that the genomes of the other species of Hystrix are different from the StH genome of Hy. patula (Jensen&Wang1997; Svitashev et al.1998; Muramatsu2001; Zhang et al.2002; Zhang and Zhou2006; Zhang et al.2006). Jensen&Wang (1997) proposed that Hy. coreana and Hy. californica had the same genome constitution NsXm as Leymus Hochst., and combined these two species into Leymus. The chromosome pairing and genomeinsitu hybridization (GISH) analyses indicated that Hy. coreana, Hy. duthiei and Hy. duthiei ssp. longearistata shared the NsXm genomes of Leymus, and should be treated as species of Leymus (Zhang et al.2006; Zhang&Zhou2006). Based on the Southen and GISH analysis, Ellneskog-Staam et al.(2007) advocated that Hy. komarovii most likely had a variant of the StH genome of Hy. patula, and should be transferred to the genus Elymus. It was also considered that Hy. coreana, Hy duthiei and Hy. duthiei ssp. longearistata had the Ns'Ns2genome constitutions (Ellneskog-Staam et al.2007). Therefore, the definition of Hystrix and its precise taxonomic status are still under discussion today. Some authors included the species in either Hystrix (Sakamoto1973; Kuo1987; Osada1993; Baden et al1997; Zhou et al.2000) or Asperella (Keng1959; Baum1983; Ohwi1984; Koyama1987), while others regarded it as a part of Elymus (Dewey1982; Love1984) or Leymus (Jensen&Wang1997; Zhang et al.2006). Now the disputes about Hystrix are:whether it is a valid genus? What are the genome constitutions of Hystix species? How about the phylogenotic relationships between Hystrix and its related species?
In order to inspect the genomic constitution of Hystrix species and their precise taxonomic status, and relationship between Hystrix and Leymus, the leaf epidermal micromorphology, lamina anatomy, interspecific hybridization, chromosome pairing behavior at MI, genomic in situ hybridization (GISH), molecular phylogenetic analysis from chloroplast atpB-rbcL, nuclear RPB2and ITS sequences for Hystrix species and their related species were carried out in this study. The main results showed as follows:
1. To reveal the phylogenetic relationships and maternal donor of species in Hystrix and Leymus, the chloroplast atpB-rbcL sequences were analyzed for Hystrix and its related species. The results indicated that:(1) Hy. patula was closely related to Elymus, and the maternal donor of Hy. patula was the St genome;(2) Hy. duthiei and Hy. duthiei ssp. longearistata were closely related to the Eurasia Leymus, and the maternal donor of them were the Ns genome from Psathyrostachys;(3) Hy. coreana and Hy. komarovii were closely related to the Leymus species in North America, and their maternal donors might be the Xm genome.
2. Low copy nuclear gene RPB2was analyzed for Hystrix and its related species. The results showed:(1) Ns copy sequences of RPB2of Hystrix and Leymus have more diversity than that in Psathyrostachys, and Tajima's and Fu and Li's D values were all negative significant for RPB2gene on the Ns and Xm genome, indicated that population expansion and rapid genetic differentiation might have occurred among the species with NsXm genome in Leymus and Hystrix;(2) More than2copies of RPB2in Hy. coreana, Hy. duthiei, Hy. duthiei ssp. longearistata, L. karelinii, L. innovatus, L. paboauns, L. salinus, L. shanxiens and L. mollis were obtained, and7sequences from Hy. coreana, Hy. duthiei, L. salinus and L. karelinii were detected as recombination sequenses;(3) Hy. patula was closely related to Pseudoroegneria, Hordeum and Elymus;(4) Hy. duthiei, Hy. duthiei ssp. longearistata, Hy. coreana and Hy. komarovii contain NsXm genome, and were closely related to Psathyrostachys and Leymus;(5) H genome of Hordeum may involve in the composition of Xm genome by introgression;(6) L. mollis distributed in North America might have migrated from Central Asia, and have close relationship with L. multicaulis; L. mollis might have gene exchange with the species contained StH genome by some way.
3. Sequence and phylogenitical analysis were carried out for ITS sequence from species of Hystrix and Leymus combined with30diploid species in Triticeae. The results were:(1) abundent ITS polymorphism were detected among Hystrix and Leymus, and the pattern of rDNA variation is associated with geographic distribution pattern;(2) Ns-genomic types of Hystrix and Leymus were originated from Psathyrostachys, P/F and St genomic types of Leymus were originated from AgropyronlEremopyrum, and Pseudoroegneria species, respectively;(3) the occurrence of a higher proportion of Hystrix and Leymus species with dominant uniparental rDNA type may associated with the segmental allopolyploid origin, and adaptive radiation in Hystrix and Leymus.
4. A total of23interspecific or intergeneric cross combinations involving Hystrix and Leymus species were performed, and13hybrid F1plants were obtained. Meiosis analysis of3hybrids from species of Leymus were carried out. Meiosis analysis showed that:(1) in the tetraploid hybrids of L. multicaulis x L. crassiusculus, L. qinghaicus x L. multicaulis, and L. multicaulis x L. qinghaicus, an average of12.87,12.07and11.97bivalents per cell was observed at MI, respectively, suggesting that L. crassiusculus and L. qinghaicus share the same basic NsXm genome of L. multicaulis. Thus, it is reasonable that L. crassiusculus and L. qinghaicus were treated in Leymus.
5. Genomic in situ hybridization (GISH) analysis was carried out in three Hystrix species (Hy. komarovii, Hy. coreana and Hy. duthiei ssp. longearistatd) and4Leymus species (L. flexus, L. mundus, L. racemosus and L. secalinus). GISH analysis indicated that:(1) Hy. komarovii has the NsXm genome instead of the StH genome;(2) Hy. komarovii, Hy. coreana and Hy. duthiei ssp. longearistata have the NsXm genomeof Leymus;(3) in species of Leymus, the Xm genome is closely related to Ns genome, and the Xm genome may be another Ns genome;(4) Ee genome is homology with the NsXm genome in a lower degree;(5) Xm genome did not origin from P genome.
6. The leaf epidermal micromorphology and anatomical structure of Hystrix, Leymus and Elymus was examined under light microscope. The results showed that:(1) a number of variations of epidermal micromorphology and anatomical structure exist at the species level, and may be used for distinguishing different speicies, but not for different genera;(2) variations of epidermal features includes variation in morphology and wall thickness of long cells, morphology and distribution patterns of short cells and distribution of prickles;(3) the leaf anatomical features such as the presence or absence of keel, the outline of keel if it is present, arrangement of vascular bundles, have more distinguishing value between different species;(4) the variation of epidermal micromorphology and anatomical structure is related closely to environment.
引文
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