Genomic and genetic relationships among species of Leymus (Poaceae: Triticeae) inferred from 18S-26S ribosomal genes

The 18S-26S ribosomal genes in three closely related species of Leymus (Poaceae: Triticeae) were examined using fluorescence in situ hybridization (FISH) and restriction fragment length polymorphism (RFLP). Both approaches revealed a close relationship between L. arenarius (8x = 56, northern European) and L. racemosus (4x = 28, central Eurasian), whereas L. mollis (4x = 28, northern American/Pacific) was distinct. Each species had three homologous pairs of major rDNA loci: a1, a2, and a3 for L. arenarius; m1, m2, and m3 for L. mollis; and r1, r2, and r3 for L. racemosus. Leymus arenarius had in addition three minor loci, a4, a5, and a6. The major loci of L. arenarius and L. racemosus were identical, indicating that the former species could have originated from the latter, via interspecific hybridization and/or polyploidy. The rDNA-RFLPs further indicated relationships of these species to other species of Leymus (L. karellini, 8x = 56 and L. angustus, 12x = 84) and Psathyrostachys (P. fragilis, P. huashanica, P. juncea, and P. lanuginosa, which are all diploids). A phenogram constructed from 20 BamHI, EcoRI, and DraI rDNA fragments revealed closer relationship between the two genera, Leymus and Psathyrostachys, than that among species within a genus.     

Molecular variation in Leymus species and populations

Icelandic populations of European lymegrass [Leymus arenarius (L.) Hochst.] were examined using amplified fragment length polymorphism (AFLP) and restriction fragment length polymorphism (RFLP) of the major ribosomal genes (18S-5.8S-26S rDNA), in comparison with Alaskan populations of its closely related species L. mollis (Trin.) Pilger. The AFLP profiles emerged as two distinct entities, clearly separating the two species, and based on species-specific bands it was simple to distinguish these two morphologically similar species. The rDNA-RFLPs also differentiated the species. Within species, the Icelandic L. arenarius was more homogeneous than the Alaskan L. mollis, and its variation was dispersed over geographically different populations, suggesting a common gene pool. The variation among the Alaskan L. mollis was more extensive and its interrupted pattern may be the result of gene introgression at subspecies level. Within a 40-year-old population of L. mollis established in Iceland from Alaskan material, the molecular profiles separated old and new genotypes. Both AFLP and rDNA revealed the new genotypes to be extremely similar. This rapid change in allele frequency is thought to be the result of adaptation to a new environment.     

Isolation, characterization, and analysis of Leymus-specific DNA sequences.

Genomic Southern hybridization using labeled total genomic DNA of Leymus mollis as probe showed intense hybridization signals on all restriction enzyme digested DNA from five species of Leymus Hochst., and four species of Psathyrostachys Nevski. Experiments using the same L. mollis probe, but with unlabeled blocking DNA from Psathyrostachys, showed no hybridization at all. These two genera evidently had the same genomic content. Southern hybridization without blocking allowed identification of DNA fragments abundant in Leymus and Psathyrostachys. Fragments potentially specific to Leymus were cloned. Five repetitive DNA clones from L. mollis and L. arenarius were characterized: pLmIs1, pLmIs44, pLmIs51, pLmIs53, and pLaIs56. These clones hybridized to both Leymus and Psathyrostachys on Southern blots - no clone hybridized to only one of these genera. Both Southern blot and fluorescence in situ hybridization (FISH) experiments showed that all the clones contained dispersed repetitive sequences. They painted all and whole chromosomes uniformly except at centromeres, telomeres, and nucleolar organiser regions. Three of these clones, i.e., pLmIs1, pLmIs44, and pLmIs53, were essentially specific to Leymus and Psathyrostachys - little or no hybridization was detected in other genera such as Triticum, Hordeum, Thinopyrum, or Elymus. Sequence analysis further revealed that the clones were part of retroelements. In particular, the clone pLmIs44 produced hybridization profiles suitable for analysis of genetic relatedness among species. The present study shows that Leymus and Psathyrostachys share the same basic genome, Ns, and therefore provides strong evidence for combining these two genera.     

Absence of the J genome in Leymus species (Poaceae: Triticeae): evidence from DNA hybridization and meiotic pairing.

To test the presence of a J genome in the type species of Leymus, L. arenarius, its total genomic DNA and that of tetraploids L. mollis, L. salinus ssp. salmonis, L. ambiguus, L. chinensis, L. secalinus, L. alaicus ssp. karataviensis, and L. innovatus were probed with the 277-bp insert of pLeUCD2, which can hybridize with the J, S, and P but not with the N, R, V, Q, I, T, and ABD genomes. The DNA probe hybridized with PalI- or TaqI-digested total DNAs from Thinopyrum elongatum (JeJe diploid) and T. elongatum x Psathyrostachys juncea (JeN hybrid), but not with those from L. arenarius (NNNNXXXX octoploid) and all tetraploid Leymus species (NNXX). Attempts to cross diploid Thinopyrum and tetraploid Leymus species yielded only one triploid hybrid, T. elongatum x L. salinus ssp. salmonis. Meiotic chromosome associations at metaphase I of pollen mother cells in the triploid hybrid averaged 19.69 univalents, 0.64 bivalents, and 0.01 trivalents per cell. Chromosome pairings in the tetraploid hybrids of L. mollis x L. salinus ssp. salmonis, and the reciprocal cross, indicate that L. mollis and L. salinus ssp. salmonis shae the same genomic constitution. Both the DNA probe and genome analysis results confirm the absence of the J genome in the seven additional Leymus species tested. Meiotic data indicated that tetraploid Leymus species could not have the genome formula N1N1N2N2; thus their genome formulas should remain as NNXX until the source of X is identified.     

Variations in abundance of 2 repetitive sequences in Leymus and Psathyrostachys species.

The Ns genome of the genus Psathyrostachys is a component of the polyploid genome in the genus Leymus. Using fluorescence in situ hybridization (FISH), the occurrence and abundance of 2 tandem repetitive sequences from Leymus racemosus (Lam.) Tzvelev, pLrTaiI-1 (TaiI family) and pLrPstI-1 (1 class of 350-bp family), were assayed in 4 species of the genera Psathyrostachys and Leymus. The pLrPstI-1 sequence was absent in all 4 Psathyrostachys species. While P. fragilis and P. huashanica did not have the pLrTaiI-1 sequence, 15 accessions of P. juncea and 2 accessions of P. lanuginosa had pLrTaiI-1 sites ranging in number from 7 to 16 and from 2 to 21, respectively. The numbers of pLrTaiI-1 and pLrPstI-1 sites were 1-24 and 0-30, respectively, in L. ramosus; 2-31 and 5-36 in L. racemosus; 0-4 and 0 in L. mollis; 2-9 and 24-27 in L. secalinus. The FISH assay on pLrTaiI-1 was successfully converted to a sequence-tagged-site polymerase chain reaction (STS-PCR) test using a primer pair designed from the sequence of this repetitive DNA. Seventy-three accessions representing 27 Leymus species were assayed for the abundance of pLrTaiI-1 by STS-PCR. With a few exceptions of uniformity in some accessions, nearly all Leymus species observed were heterogeneous for the abundance of pLrTaiI-1 sequence and no Leymus species was totally devoid of this repetitive sequence. These findings may have significance for the understanding of phylogeny, nature of polyploidy, adaptive ranges, and breeding potential of Leymus species.     

Identifying the genome of wood barley Hordelymus europaeus (Poaceae: Triticeae)

Wood barley, Hordelymus europaeus, was compared with other Triticeae species by Southern and fluorescence in situ hybridisation using total genomic DNA and repetitive sequences as probes. On Southern blots, the total genomic probe from H. europaeus hybridised strongly to DNA of its own species and to Leymus and Psathyrostachys, indicating the presence of Ns genome in H. europaeus. Furthermore, the total genomic probe from P. fragilis hybridised to DNA of H. europaeus as much as to all of the Psathyrostachys and Leymus species examined. Ns genome-specific DNA sequences isolated from L. mollis (pLmIs1, pLmIs44 and pLmIs53) hybridised essentially to H. europaeus and all of the species of Leymus and Psathyrostachys. Chromosomal localization of these clones on H. europaeus confirmed the presence of Ns genome-specific DNA on all chromosomes, indiscriminately. Under moderate hybridisation stringency the Ns genome-specific probes, together with repetitive sequences pTa71 and pAesKB7, produced species-specific RFLP banding profiles on Southern blots. A phenetic tree based on these profiles revealed a distinct Ns species cluster within the Triticeae, represented by Leymus and Psathyrostachys species. Hordelymus europaeus belonged to this Ns cluster. Chromosomal mapping of the 18S-25S and the 5S ribosomal genes, together with the repetitive sequence pLrTaiI, corroborated that H. europaeus was most probably related to Leymus, especially the European/Eurasian members of sect. Leymus. In an attempt to identify the genome of H. europaeus, different approaches were employed; the results clearly showed that wood barley had the Ns basic genome and nothing else.     

Coexistence and hybridization of Leymus mollis and L. arenarius in Greenland, and demarcation of the species by endospermal prolamins, leymins

The occurrence of Leymus arenarius as a constituent of the Greenlandic flora is confirmed. The different patterns of hairiness of the rachis segments characteristic of L. mollis and L. arenarius , respectively, were found to correlate with endospermal protein patterns fractionated with SDS-PAGE (sodium dodecylsulphate, polyacrylamide gel electrophoresis). The characteristics of its protein patterns were substantiated by a transect study of L. arenarius through Fennoscandia. The northern populations of L. mollis and L. arenarius displayed no or relatively little variation in endospermal protein patterns within plants or sites. This may reflect a prevailing self-pollination, founder effect, clonal spreading of stands and selection or any combination thereof. The key proteins of 120 to 140 kg mole^-1 demarcating L. mollis and L. arenarius were shown to be soluble in 50% isopropanol at pH 8.0, and hence to be prolamins, which were also found to carry glycosylation. The spontaneous, sterile hybrids of these species in Greenland have an intermediary morphology. A hybrid clone may form relatively wide stands in South and Southwest Greenland.     

猬草及其近缘属植物单拷贝核Pgk1基因序列的系统发育分析

文章对禾本科小麦族猬草属及其近缘属Thinopyrum(Eb)、Lophopyrum(Ee)、拟鹅观草属(St)、新麦草属(Ns)、大麦属(H)、赖草属(NsXm)和披碱草属(StH)植物共23个类群的单拷贝核Pgk1基因序列进行系统发育分析, 探讨猬草属及其近缘属植物的系统发育关系。序列分析发现Pgk1基因序列在L. arenarius和Psa. juncea中有81 bp的Stowaway家族DNA转座元件插入, 而在Hy. duthiei、Hy. duthiei ssp. longearistata和L. akmolinensis中有29 bp Copia家族的反转录转座元件插入。最大似然和贝叶斯推断进行的系统发育分析表明: (1)猬草属模式种Hy. patula与披碱草属、拟鹅观草属和大麦属具有密切的亲缘关系; (2)猬草属的其他物种Hy. duthiei、Hy. duthiei ssp. longearistata、Hy. coreana和Hy. komarovii与新麦草属和赖草属植物亲缘关系密切。研究结果支持将Hy. patula从猬草属组合到披碱草属中, 而Hy. duthiei、Hy. duthiei ssp. longearistata、Hy. coreana和Hy. komarovii应组合到赖草属中。     

Phylogenetic relationships in Leymus (Poaceae: Triticeae) revealed by the nuclear ribosomal internal transcribed spacer and chloroplast trnL-F sequences

Using the nuclear ribosomal internal transcribed spacer (ITS) sequences and the chloroplasttrnL-F sequence, phylogeneic analysis was performed on 57 accessions of species in the tribe Triticeae including 13 Leymus species (N(s)) with different ploidy levels and 40 diploid species from 18 genera. The ITS sequences revealed that ployploid Leymus has close phylogentic relationships with Psathyrostachys and an undefined genus in Triticeae. The trnL-F tree demonstrated close relationships between certain Leymus species and Psathyrostachys, and other Leymus species distributed in North America were far from Psathyrostachys. Based on these results, it is unlikely that the unknown genome in Leymus species originated from one of the sampled diploid species in the present study. The maternal donor of all the Leymus species with a natural distribution in Eurasia were N(s) genome. Furthermore, Elymus californicus should be transferred from the genus Elymus to Leymus.     

Fluorescence in situ Hybridization and Southern Blot Analyses on Leymus racemosus and Related Species

Fluorescence in situ hybridization (FISH) was carried out in somatic cells of racemosus (lam.) Tzvel. and Thinopyrum junceum ( Savul. & Rayss) A. Love using Th. bessarabicum ( Savul. & Rayss) A. Love genomic DNA as probe. Fourteen pairs of chromosomes in L. racemosus gave positive signal, and only seven of fourteen pairs of chromosomes in Th. junceum showed signal. In FISH probed with PHv62, the chromosomes in Th. bessarabicum and L. racemosus hybridized with PHv62, whereas Th. Bessarabicum showed positive signal in four pairs of chromosomes, and the latter in thirteen pairs of chromosomes. No positive signal was observed in chromosomes of Psathyrostachys juncea (Fisch.) Nevski and Th. junceum. The results of Southern hybridization probed with PHv62 were similar to those of in situ hybridization. Twelve alien chromosome lines of T. aestivum-L, racemosus were detected by PHv62 probing. In most of the alien chromosome lines, PHv62 hybridized in fragment of Leymus chromosomes, except for the line containing chromosomes 5Lr # 1 and 1 1Lr # 1. It is inferred that Th. bessarabicum may involve in the formation of species. Non the less, significant changes have occurred during the evolution of Leymus genomes.     

Phylogeny of Hystrix and related genera (Poaceae: Triticeae) based on nuclear rDNA ITS sequences

The taxonomic status of Hystrix and phylogenetic relationships among Hystrix and its related genera of Pseudoroegneria (St), Hordeum (H), Psathyrostachys (Ns), Elymus (StH), Leymus (NsXm), Thinopyrum bessarabicum (E(b)) and Lophopyrum elongatum (E(e)) were estimated from sequences of the internal transcribed spacer (ITS) region of nuclear ribosomal DNA. The type species of Hystrix, H. patula, clustered with species of Pseudoroegneria, Hordeum, Elymus, Th. bessarabicum and Lo. elongatum, while H. duthiei ssp. duthiei, H. duthiei ssp. longearistata, H. coreana and H. komarovii were grouped with Psathyrostachys and Leymus species. The results indicate that: (i) H. patula is distantly related to other species of Hystrix, but is closely related to Elymus species; (ii) H. duthiei ssp. duthiei, H. duthiei ssp. longearistata, H. coreana and H. komarovii have a close affinity with Psathyrostachys and Leymus species, and H. komarovii might contain the NsXm genome of Leymus; and (iii) the St, H and Ns genomes in Hystrix originate from Pseudoroegneria, Hordeum and Psathyrostachys, respectively, while the Xm in Hystrix and Leymus has a complex relationship with the E or St genomes. According to the genomic system of classification in Tiritceae, it is reasonable to treat Hystrix patula as Elymus hystrix L, and the other species of Hystrix as species of a section of Leymus, Leymus Sect. Hystrix.     

Genetic diversity and phylogeny in Hystrix (Poaceae, Triticeae) and related genera inferred from Giemsa C-banded karyotypes

The phylogenetic relationships of 15 taxa from Hystrix and the related genera Leymus (NsXm), Elymus (StH), Pseudoroegneria (St), Hordeum (H), Psathyrostachys (Ns), and Thinopyrum (E) were examined by using the Giemsa C-banded karyotype. The Hy. patula C-banding pattern was similar to those of Elymus species, whereas C-banding patterns of the other Hystrix species were similar to those of Leymus species. The results suggest high genetic diversity within Hystrix, and support treating Hy. patula as E. hystrix L., and transferring Hy. coreana, Hy. duthiei ssp. duthiei and Hy. duthiei ssp. longearistata to the genus Leymus. On comparing C-banding patterns of Elymus species with their diploid ancestors (Pseudoroegneria and Hordeum), there are indications that certain chromosomal re-arrangements had previously occurred in the St and H genomes. Furthermore, a comparison of the C-banding patterns of the Hystrix and Leymus species with the potential diploid progenitors (Psathyrostachys and Thinopyrum) suggests that Hy. coreana and some Leymus species are closely related to the Ns genome of Psathyrostachys, whereas Hy. duthiei ssp. duthiei, Hy. duthiei ssp. longearistata and some of the Leymus species have a close relationship with the E genome. The results suggest a multiple origin of the polyploid genera Hystrix and Leymus.     

大赖草染色体组构成的生化分析

本文通过对不同来源大赖草及其可能供体物种的EST、GOT、SOD同工酶及HMW-GS的分析, 发现不同来源大赖草的同工酶及蛋白图谱呈一定差异,但其中为不同来源大赖草所共有的一些谱带, 同时也存在于具N染色体组物种的分析图谱中,而在具J染色体组的物种中却没有特异性分布,推断大赖草中含有N染色体组,但可能不含J染色体组。 Abstract:The zymogram phenotypes of Esterase(EST),Glutamate oxalocate transminase(GOT),Superoxide dismutase(SOD)and the banding patterns of high molecular weight glutenin subunits(HMW-GS) were determined for different Leymus racemosus accessions and their putative donor species,It was found that although the zymogram phenotypes and the HMW-GS banding patterns appeared polymorphism,common bands for different Lr accessions were found in the species with N genome,but not in those with J genome,suggesting that the Psathyrostachys species with N genome must be phylogenetically closer to Lr,while the Thinopyrum species with J genome are farther to it.     

赖草的种间和属间杂种胚胎培养研究

以小麦族赖草属植物的６个种：赖草（Ｌｅｙｍｕｓｓｅｃａｌｉｎｕｓ）、窄颖赖草（Ｌ．ａｎｇｕｓｔｕｓ）、单小穗赖草（Ｌ．ａｅｍｕｌａｎｓ）、多枝赖草（Ｌ．ｍｕｌｔｉｃａｕｌｉｓ）、大赖草（Ｌ．ｒａｃｅｍｏｓｕｓ）和天山赖草（Ｌ．ｔｉａｎｓｈａｎｉｃｕｓ）作试验材料,分别组配成５个种间杂交组合,并与新麦草属（Ｐｓａｔｈｙｒｏｓｔａｃｈｙｓ）、鹅观草属（Ｒｏｅｇｎｅｒｉａ）以及Ｔｈｉｎｏｐｙｒｕｍ属组配成９个属间杂交组合。应用胚胎培养技术,离体培养杂种胚胎,成功地拯救了赖草植物的种间和属间杂种。试验结果表明,杂种胚胎的胚龄、培养基的营养组成以及杂种基因型对离体胚胎的培养有明显影响。     

Molecular cytogenetics of Leymus: Mapping the Ns genome-specific repetitive sequences

The objective of this paper is to summarize the work in my group on FISH (fluorescent in situ hybridization) mapping of Ns-specific repetitive DNA sequences fromLeymus and discuss the results in the context of classification based on the genome system currently used among Triticeae researchers. The key question here is whether the genome composition of a tetraploid Leymus species should be NsXm or NsNs (Ns₁Ns₂). Different types of Leymus-specific dispersed retroelement-like repeats have been isolated and characterized. Because the sequences occur in significantly high copy number in Leymus, based on strong hybridization signal in Southern blots, they are considered essentially specific to Leymus. They are also abundant in Psathyrostachys, the progenitor of Ns genome in Leymus. These dispersed repeats are found to distribute over the whole of all Leymus chromosomes, without any differentiation between chromosomes that have been suggested to be of different genomic origins, meaning that all genomes in Leymus are the same. GISH (genomic in situ hybridization) experiments on Leymus chromosomes using Psathyrostachys genomic DNA as probes further support the NsNs (Ns₁Ns₂) genome constitution for Leymus. The Xm genome of an unknown origin might have been there in the beginning of the allopolyploidization process, but the Ns genome-specific elements must have spread predominantly and rapidly across genomes, thus homogenizing the nuclear genomes of Leymus. I present here for the first time evidence that Ns-specific dispersed repeats can spread in a very short time, from Leymus over to wheat in Triticum × Leymus hybrids growing in artificial conditions.     

基因组分析与小麦抗病育种

系统总结了南京农业大学细胞遗传研究所近 2 0多年来利用基因组分析方法培育从簇毛麦 (Haynaldiavil losaSch .)、大赖草 (LeymusracemosusLam .)、鹅观草 (RoegneriakamojiC .Koch)和纤毛鹅观草 (R .ciliaris (Trin .)Nevs ki)导入白粉病和赤霉病抗性的小麦种质的研究进展。利用染色体C_分带、基因组原位杂交、分子标记 (特别是RFLP)等技术与非整倍体分析相结合对所创制的种质进行了系统分析与鉴定。还对所培育的小麦种质在育种实践和理论研究中的潜在价值及相关问题进行了讨论     

Phylogenetic Analysis of Leymus (Poaceae: Triticeae) Inferred from Nuclear rDNA ITS Sequences

To investigate the phylogenetic relationships of polyploid Leymus (Poaceae: Triticeae), sequences of the nuclear rDNA internal transcribed spacer region (ITS) were analyzed for 34 Leymus accessions representing 25 species, together with three Psathyrostachys species (Ns genome), two Pseudoroegneria (St genome) species, Lophopyrum elongatum (E(e) genome), and Thinopyrum bessarabicum (E(b) genome). The phylogenetic analyses (maximum likelihood and Bayesian inference) supported two major clades, one including 21 Leymus species and three Psathyrostachys species, the other with nine Leymus species and four diploid species. The ITS RNA secondary structure of the Leymus species was compared with that of their putative diploid donor. It is suggested that (1) the species from the same areas or neighboring geographic regions are closely related to each other; (2) L. coreanus, L. duthiei, L. duthiei var. longearistatus, and L. komarovii are closely related to other Leymus species, and it is reasonable to transfer these species from the genus Hystrix to Leymus; (3) the ITS sequences of Leymus are evolutionarily distinct; (4) the different Leymus species and different distribution of a species derived their Ns genome from different Psathyrostachys species; and (5) there is a close relationship among Leymus, Pseudoroegneria, Lophopyrum, and Thinopyrum, but it is difficult to presume that the St, E(e), and E(b) genome may be the Xm genome donor of the Leymus species.     

Spontaneous tetraploidy in strawberry (Fragaria sp., Rosaceae)

A tetraploid (2n = 28) clone of Fragaria from SW Finland is described. The clone is true-breeding with respect to tetraploidy. The tetraploid strawberry shows RFLP similarity with F. vesca , a common species, and, to a lesser extent, with F. viridis , a southern species, whose nearest reported occurrence was about 80 km away during the 1940s. The following alternatives are considered as possible reasons for the tetraploidy: unreduced gametes in an interspecific hybrid or hybrid derivative; hybridization followed by induction of tetraploidy either by viruses, or by industrial pollutants, e.g. chlorophenols and their congener compounds in the soil. The original seed might also have been brought from abroad unintentionally with other seeds for field trials which have been conducted since 1928 in the vicinity. A hexaploid ( F. moschata )× diploid hybrid leads directly to tetraploidy and a tetraploid derivative from an octoploid ( F . × ananassa ) × diploid hybridization can be obtained but the current tetraploid has different morphology.     

Characterization and distribution of an interspersed repeated nucleotide sequence from Lophopyrum elongatum and mapping of a segregation-distortion factor with it

Repeated nucleotide sequence pLeUCD2 cloned from Lophopyrum elongatum is highly abundant in the genomes of diploid and polyploid wheatgrass species of genera Lophopyrum, Thinopyrum, Pseudoroegneria, Agropyron, Elymus, Elytrigia, and Pascopyrum but undetectable by Southern blot hybridization in Triticum and representative species of Dasypyrum, Hordeum, Psathyrostachys, Secale, Taeniatherum, Heteranthelium, and Leymus in the tribe Triticeae. The DNA fragment inserted in pLeUCD2 is 277 bp long and AT rich (65%), and contains numerous inverted and palindromic repeats. In situ DNA hybridization substantiated a previous hypothesis that the sequence is interspersed in the wheatgrass genomes. Heterogeneity and clustering of like repeats of the pLeUCD2 family along wheatgrass chromosomes was used to map a segregation-distortion factor, designated Sd-1, proximal to the Lr19 locus in recombinant chromosomes of L. ponticum chromosome 7Ag and wheat chromosome 7D.     

大赖草总DNA转化小麦的分子证据

用来自大麦组的４个高度重复序列克隆了ｐＨｖ７１６１,ｐＨｖ７１７８９,ｐＨｖ７１９１、ｐＨｖ７２９３,经地高辛和同位素２种方法标记后作为探针,对新疆大赖草（供体）、春麦７６１（受体）以及用大赖草总ＤＮＡ通过花粉管通道转化成功的大穗转化株基因组在高度严谨条件下进行了分子杂交。结果表明,这４个探针可以探查出基因内一种具有主串产重复单位的散在重复序列。比较受共体和转化体的杂交图谱,发现在转化株中出现了