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1.
Sharma R Jana S 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》2002,105(2-3):306-312
Random amplified polymorphic DNA (RAPD) markers were used to distinguish between 28 different accessions belonging to 14 species and two sub-species of Fagopyrum. Of the 75 random 10-mer primers tested, only 19 generated robust, easily interpretable amplification products. A total of 364 bands were observed with an average of 19.15 bands per primer, of which 99.45% were polymorphic. Primer OPN-08 produced the maximum number of fragments and UBC-183 produced the minimum number of fragments. The data were utilized to elucidate genetic relationships among 14 species and two sub-species of Fagopyrum. Cluster analysis using the unweighted paired group method of arithmetic means (UPGMA) showed four main clusters, two each of the cymosum and urophyllum groups. The results showed that Fagopyrum tataricum is closer to its wild ancestor F. tataricum ssp. potanini Batalin, closely followed by Fagopyrum giganteum. Cultivated common buckwheat ( Fagopyrum esculentum) showed affinity with its putative wild ancestor F. esculentum ssp. ancestrale and the other closely related diploid species Fagopyrum homotropicum. In the urophyllum group, Fagopyrum macrocarpum and Fagopyrum pleioramosum formed one cluster, whereas Fagopyrum capillatum, Fagopyrum gracilipes and Fagopyrum gilessii clustered separately. Except for a few cases, our results correspond with previously reported studies on Fagopyrum using the isozyme, RFLP and RAPD methods. Species-diagnostic amplification products specific to some species in the cymosum and urophyllum groups were identified. Our results show that RAPDs can be successfully used to analyze species relationships in Fagopyrum and also for constructing linkage maps. 相似文献
2.
Fagopyrum urophyllum is a cross-pollinating perennial woody shrub species belonging to the urophyllum group of Fagopyrum. Natural populations of F. urophyllum were morphologically classified into two distinct groups, the Dali group and the Kunming group without exception. This grouping was verified by molecular phylogeny based on the nucleotide sequence of chloroplast DNA. The reproductive isolation found between the two groups was almost perfect as the distribution of two groups did not overlap each other. The net nucleotide substitution rate (Da) between the two groups was at the same level as between two distinct species. These data suggests that the two groups should be classified into distinct species if future studies on F. urophyllum confirm complete reproductive isolation and no ambiguously classified populations in the border area of the central Yunnan province of China. 相似文献
3.
Search for the wild ancestor of buckwheat III. The wild ancestor of cultivated common buckwheat, and of tatary buckwheat 总被引:1,自引:0,他引:1
Ohmi Ohnishi 《Economic botany》1998,52(2):123-133
By surveying wild Fagopyrum species and their distribution in southern China and the Himalayan hills, I arrived at the conclusion
that the newly discovered subspecies F. esculentum ssp. ancestralis Ohnishi is the wild ancestor of cultivated common buckwheat,
while previously known wild tatary buckwheat,F. tataricum ssp. potanini Batalin is the wild ancestor of tatary buckwheat. Their original birthplace is revealed to be northwestern
corner of Yunnan province for common buckwheat judging from the distribution of wild ancestor, and to be the northwest part
of Sichuan province for tatary buckwheat judging from allozyme variability in wild tatary buckwheat. F. cymosum is not the
ancestor of cultivated buckwheat; it is only distantly related to cultivated buckwheat, in morphology, isozymes and cpDNA.
Several genetic, ecological and taxonomic categories which should be taken into consideration in examining the origin of buckwheat
were discussed. Key Words: Fagopyrum esculentum ssp. ancestralis; Fagopyrum tataricum ssp. potanini; southern China theory
of origin of buckwheat.
Contribution from Plant Germ-Plasm Institute, Faculty of Agriculture, Kyoto University. No. 78. 相似文献
4.
Nucleotide sequence polymorphisms of the intron of the chloroplast trnK (UUU) gene, including a matK gene, were investigated within two wild Fagopyrum species, F. leptopodum and F. statice, to assess the degree and pattern of the inter- and intraspecific differences in coding and noncoding chloroplast DNA regions in higher plants. Ten and five accessions were used for F. leptopodum and F. statice, respectively. The length of the trnK intron region in these species ranged from 2494 to 2506 bp. In the trnK intron, the net nucleotide substitution number per site (Da) between the two species was 0.00109, lower than the nucleotide diversity (pi), 0.00195 for F. leptopodum and 0.00144 for F. statice, suggesting a low level of interspecific divergence. This result seems to be due to the phylogenetic pattern that both species are interspersed with each other, which was revealed by the phylogenetic analyses based on the nucleotide substitutions and indels. In the matK gene region (1524 bp), seven and two nucleotide substitutions were found within F. leptopodum and F. statice, respectively. All of the nine nucleotide substitutions (eight of which were nonsynonymous) within and between F. leptopodum and F. statice were clustered in the 5' part of the matK gene region, and no variation was found in the 3' part. This suggests that most of the 3' part is occupied by the conserved domains that are important for the binding activity of the gene product to the precursor mRNA, and therefore implies that the 3' part is more functionally constrained than the 5' part. 相似文献
5.
Two new Fagopyrum (Polygonaceae) species, F. gracilipedoides and F. jinshaense, are described. Fagopyrum gracilipedoides was only found at Baoshan village, Lijiang district, Yunnan province, China. This species resembles the weedy species, F. gracilipes in morphology but they differ in both mating system and ploidy level; F. gracilipedoides is a heterostylous self-incompatible diploid species (2n = 16), whereas F. gracilipes is a self-compatible tetraploid species (2n = 32). Fagopyrum jinshaense was found along the Jinsha River valley near the border of Sichuan, Yunnan, and Tibet in China. Fagopyrum jinshaense is morphologically similar to F. gilesii, but they differ in the morphology of their inflorescences. Fagopyrum jinshaense has long spike-like inflorescences, whereas F. gilesii has a compact head-like one. Both F. jinshaense and F. gilesii are self-incompatible with heterostylous flowers and are diploid. Interspecific crosses between the two new species and already known species in the urophyllum group of Fagopyrum resulted in the production of self- and cross-sterile hybrids in the species combinations attempted. These results indicated that both new species are reproductively isolated from other Fagopyrum species. Molecular phylogenetic analysis based on the nucleotide sequence of the trnK gene intron in chloroplast DNA revealed the following points: 1) F. gracilipedoides, F. rubifolium and F. gracilipes / F. capillatum showed a trifurcating relationship and 2) F. jinshaense formed a clade with F. pleioramosum, F. callanthum, and F. macrocarpum, and was only distantly related to F. gilesii. In the clade of F. capillatum, F. gracilipes, F. gracilipedoides and F. rubifolium, the breakdown of self-incompatibility accompanying genome duplication seems to have occurred twice independently. 相似文献
6.
We performed phylogenetic analyses of Fagopyrum species in the urophyllum group based on nucleotide sequences of two nuclear genes, FLORICAULA/LEAFY (FLO/LFY) and AGAMOUS (AG), and three segments of chloroplast DNA (cpDNA), rbcL-accD, trnK intron, and trnC-rpoB spacer. The FLO/LFY and AG sequences turned out to be phylogenetically more informative at the intrageneric level than the cpDNA sequences. Congruence among these gene trees, inferred by a maximum-likelihood (ML) method, demonstrated that topologies were partially incongruent between the nuclear and chloroplast DNA phylogenies. The nuclear DNA sequence data supported a monophyletic relation of F. statice, F. gilesii, and F. jinshaense, whereas the former two species formed another monophyletic relation with the F. capillatum-F. gracilipes-F. gracilipedoides-F. rubifolium clade excluding F. jinshaense in the synthetic cpDNA phylogeny. In addition, two divergent sequences of FLO/LFY were found in F. rubifolium (tetraploid). One of these was sister to F. gracilipedoides and another was sister to F. statice, and a monophyletic relation of these two genes was rejected by a bootstrap analysis. These results suggest that hybridization may have occurred during diversification of Fagopyrum species in the urophyllum group, and that F. rubifolium is possibly allotetraploid species. 相似文献
7.
DNA sequences of the rbcL and accD 5' coding regions and their intergenic region (IGR) were determined in 20 taxa of 12 species of Fagopyrum. By comparing the sequence data and constructing phylogenetic trees, phylogenetic relationships among Fagopyrum species were investigated. The accD 5' coding region and the IGR have evolved about five times faster than the rcbL coding region; hence the phylogenetic trees based on the data of the accD 5' coding region, the IGR, and these data combined, had higher resolution than the trees based on rcbL alone. The classification of Fagopyrum based on the DNA sequences was almost perfectly consistent with the classification by Ohnishi and Matsuoka (1996, Genes & Genetic Systems 71: 383-390). New facts and minor differences are (1) polyploidization in F. cymosum might have occurred more than once, (2) F. lineare may not be a sister species of F. leptopodum, and (3) F. pleioramosum rather than F. capillatum may be a sister species of F. gracilipes. 相似文献
8.
用聚丙烯酰胺凝胶电泳对荞麦属8个种(含大粒组7个和小粒组1个)33份材料发芽种子的酯酶同工酶进行了研究。结果表明:酯酶同工酶不同酶带合计22条,不同物种的酶带数4到8条。其中,甜荞有8条带,苦荞为7条。酶带及聚类分析表明,大粒组荞麦种的谱带与细野荞等小粒组荞麦种间差异极大,甜荞和苦荞酶带分别与大野荞和毛野荞相似,并分别与F.megaspartanium和F.pilus聚类最近,支持F.megaspartanium和F.pilus可能分别是甜荞和苦荞祖先种的假说。 相似文献
9.
Gross morphology, fruit anatomy, tepal venation, pollen morphology, chromosome number and ITS sequence of Pteroxygonum Damm. & Diels as well as other related genera (Polygonum, Fallopia, Reynoutria, Fagopyrum, and Antenoron) have been investigated to evaluate the generic status of Pteroxygonum. Pt. giraldii Damm. & Diels has three sharp horns at the base of fruit, which is distinctive among all the genera investigated. Upon observation of fruits under a light microscope (LM), the exocarp of Pt. giraldii is usually thickened and delimited by the rectangular cells with some sporadic undulating lumen, while that of Fagopyrum is thin-walled and isodiametric to rectangular in the cell shape. Analysis of tepal venation was performed under a stereomicroscope, and two types of tepal venation were found in Fagopyrum and Pteroxygonum. The type I is trifid, observed in Pt. giraldii, F. esculentum Moench, F. dibotrys (D. Don) Hara and F. tataricum (L.) Gaertn. The type II, found in F. caudatum (Sam.) A. J. Li, F. urophyllum (Bur. & Franch.) H. Gross and F. gracilipes (Hemsl.) Damm. ex Diels, has the main vein extending from tepal base with some secondary veins. Evidence from tepal venation supports the previous classification in which Fagopyrum can be divided into a large-achene group and a small-achene group. Pollen morphology was investigated under a scanning electron microscope (SEM). The exine ornamentation of Pt. giraldii was finely reticulate with lumina diameter wider than muri width. The exine ornamentation in all the examined Fagopyrum species is, however, prominently sunken punctuate. The phylogenetic analysis of nuclear ribosomal DNA (nrDNA) ITS sequences in Pteroxygonum and related genera indicated that all the species form a well-supported monophyletic group with two clades. One includes Polygonum sect. Avicularia Meisn., genus Fallopia and genus Reynoutria, and the other consists of other sections of Polygonum, genus Fagopyrum and Pteroxygonum. The latter clade can be divided into two subclades. Fagopyrum species compose the first one, while Pteroxygonum giraldii, species of Polygonum (except sect. Avicularia) and Antenoron form the second one. In consideration of the above evidence, we conclude that Pteroxygonum is an independent genus in tribe Persicarieae, and should not be merged into the genus Fagopyrum. 相似文献
10.
通过对翼蓼Pteroxygonum giraldii Damm. &; Diels及相关属(蓼属Polygonum、何首乌属Fallopia、虎杖属Reynoutria、荞麦属Fagopyrum和金线草属Antenoron)的形态观察、果实解剖学观察、花被片脉序观察、花粉形态、核型分析, 以及ITS序列的分析确定了翼蓼和荞麦F. esculentum Moench较远的亲缘关系。其中我们发现翼蓼果实基部有三个角状物明显不同于其他属果实的形态特征。翼蓼外果皮明显加厚, 并有零星散布的波状内腔, 而荞麦的外果皮很薄, 细胞不等径, 中果皮极厚。以上证据证明了翼蓼与荞麦属亲缘关系较远。在观察荞麦属和翼蓼的花被片脉络时发现了两种不同的脉序类型, 符合将荞麦属分为两个组的划分。翼蓼花被片脉序为三出状, 支持将翼蓼归为Persicarieae族。对翼蓼及荞麦属植物的花粉进行比较后, 发现荞麦属植物的花粉网孔有明显的内凹穿孔而翼蓼却没有, 结果表明二者亲缘关系较远。通过对nrDNA ITS区域序列分析得出翼蓼及相关属为一个单系类群, 含有两个稳定的分支: 第一个分支由蓼属(萹蓄组sect. Avicularia)、何首乌属、虎杖属的植物组成, 第二个分支由蓼属(刺蓼组sect. Echinocaulon、蓼组sect. Polygonum、分叉蓼组sect. Aconogonon、拳参组sect. Bistorta、翼蓼和荞麦属植物组成。同时第二个分支又分成了两个亚分支, 蓼属(刺蓼组、蓼组、分叉蓼组、拳参组)和翼蓼属Pteroxygonum植物属于第一个亚支而荞麦属植物属于第二个亚支。结果支持翼蓼不属于荞麦属的范畴。实验结果显示翼蓼是个单型属, 属于Persicarieae族。 相似文献
11.
Phylogeographical structure revealed by chloroplast DNA variation in Japanese beech (Fagus crenata Blume) 总被引:1,自引:0,他引:1
Intraspecific genetic variation in three non-coding chloroplast DNA (cpDNA) regions (trnT-L and trnL-F spacers, and trnL intron) of Japanese beech (Fagus crenata Blume) was investigated. This species is a major constituent of the typical cool-temperate deciduous forests in Japan. Twenty-one F. crenata populations from throughout Japan, and four F. japonica populations, a close relative of F. crenata, were examined. Seven haplotypes were distinguishable in F. crenata based on nucleotide substitutions and indels. Pairwise nucleotide diversities among haplotypes ranged from 0.0000 to 0.0042 for F. crenata, including F. japonica. The geographical distribution of cpDNA haplotypes was found to be highly structured in F. crenata. Four haplotypes predominated: haplotypes FC1 and FC4 are prevalent on the Pacific Ocean coast, haplotype FC6 is prevalent on the Japan sea coast from the San-in district to Hokkaido, whilst haplotype FC3 is restricted to northern Kyushu and the western-most part of Honshu. Two haplotypes (FC5 and FC7) are restricted to single populations and one haplotype (FC2) is a derivative of FC1. Each of these haplotypes, except FC2, are thought to be derived from different glacial refugia. Phylogenetic analysis showed that neither F. crenata nor F. japonica was monophyletic for the haplotypes, suggesting either ancestral polymorphism or ancient introgression between the lineages of these two Fagus species. 相似文献
12.
Background and aimsRecently, four wild Fagopyrum species, Fagopyrum crispatifolium J. L. Liu, Fagopyrum pugense T. Yu, Fagopyrum qiangcai D. Q. Bai and Fagopyrum wenchuanense J. R. Shao, have been identified and described based on their morphological characters. This study investigates the phylogenetic relationship, nucleotide sequence polymorphisms of internal transcribed spacers (ITSs) and the maturase K (matK) gene within four wild species related to western Sichuan buckwheat. F. wenchuanense is closely related to Fagopyrum gracilipes while F. qiangcai is closely related to Fagopyrum esculentum based on their morphological differences. However, F. wenchuanense is more closely related to Fagopyrum cymosum and F. qiangcai is closer to Fagopyrum lineare and Fagopyrum leptopodum from the viewpoint of the ITS, and matK analysis. In addition, F. gracilipes is closer to F. pugense and Fagopyrum crispatofolium than to F. qiangcai. F. wenchuanense belongs to the cymosum group, while F. qiangcai, F. pugense and F. crispatifolium are classified into the urophyllum group based on their morphological and molecular analysis. Conducting morphological and molecular studies provide a better understanding of evolutionary mechanisms and genetic relationships of cultivated and wild buckwheat in western Sichuan, China. 相似文献
13.
The occurrence, number of insertion sites and antisense RNA expression of micropia transposable element were studied in 26 species that belong to three subgroups (mercatorum, mulleri and hydei) of repleta group of Drosophila. Under high specific PCR, micropia sequences were detected in 11 species, but under less stringent condition, this retrotransposon was detected in all species. The widespread distribution of micropia suggests that this element was already present at the common ancestor of the repleta group of Drosophila. Southern blot analysis showed a variation from 0 to 17 different insertion sites and the occurrence of male-specific sequences. We found that the expression of the 1.0 kb micropia antisense RNA is variable among the species and tissues (soma and testis), which suggests that more than one mechanism regulates transposition in these species. Variation of amplification by PCR and of antisense RNA expression, as well as divergence of nucleotide sequences among the species allow us to suggest that at least two subfamilies of micropia transposable element are harbored by the genome of this species group. 相似文献
14.
Divergent protein coding regions in otherwise closely related androgen-regulated mRNAs 总被引:1,自引:0,他引:1
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Rat seminal vesicles serve as a model system for studying androgen action. We have sequenced and compared full length cDNAs for two major proteins (S and F) synthesised and secreted under hormonal control. Overall, mRNAS and mRNAF share 57% nucleotide sequence homology suggesting that their genes arose by duplication of a common ancestor. However, the mRNAs display a highly unusual regional distribution of sequence homology, with the untranslated regions (UTRs) being substantially more homologous than the protein-coding regions (PCRs). Detailed analysis of nucleotide substitutions at synonymous and replacement sites shows that the PCRs have evolved very rapidly. Evolutionary conservation of the UTRs is no higher than that of UTRs generally and thus provides no evidence of a specific regulatory role for the UTRs in androgen action. The primary sequences of proteins S and F have diverged so rapidly that they are the best examples of neutrally evolving proteins for which comparative nucleotide sequence data are available. However, despite their rapid divergence, the predicted higher order structures for both proteins consist largely of non-regular conformation. This is discussed in terms of their roles as structural components of the rodent copulatory plug. 相似文献
15.
基于线粒体细胞色素b基因序列的虹雉属鸟类的系统发育关系 总被引:11,自引:0,他引:11
通过雉科虹雉属(Lophophorus)、角雉属(Tragopan)、勺鸡属(Pucrasia)和血雉属(Ithaginis)7种鸟类的细胞色素b(cyt b)基因序列比较,构建的虹雉属及其近缘属的分子系统树表明:①3种虹雉构成一个单系群(monophyletic group),虹雉属与角雉属、勺鸡属构成一个单系群;②虹雉属内分为白尾梢虹雉,以及棕尾虹雉和绿尾虹雉两个演化枝。综合分子系统学、地理分布格局和形态学的证据,推测虹雉属鸟类起源于中国的横断山脉,其中繁衍生活在原地的一枝演化为白尾梢虹雉;另一枝则分别进入喜马拉雅山区(西)和中国西南部(东),向西的演化为棕尾虹雉,向东的则为绿尾虹雉。 相似文献
16.
Whole-genome sequence of Listeria welshimeri reveals common steps in genome reduction with Listeria innocua as compared to Listeria monocytogenes
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Hain T Steinweg C Kuenne CT Billion A Ghai R Chatterjee SS Domann E Kärst U Goesmann A Bekel T Bartels D Kaiser O Meyer F Pühler A Weisshaar B Wehland J Liang C Dandekar T Lampidis R Kreft J Goebel W Chakraborty T 《Journal of bacteriology》2006,188(21):7405-7415
17.
Subterminal satellite (StSat) repeats, consisting of 32-bp-long AT-rich units (GATATTTCCATGTT(T/C)ATACAGATAGCGGTGTA), were
first found in chimpanzee and gorilla (African great apes) as one of the major components of heterochromatic regions located
proximal to telomeres of chromosomes. StSat repeats have not been found in orangutan (Asian great ape) or human. This patchy
distribution among species suggested that the StSat repeats were present in the common ancestor of African great apes and
subsequently lost in the lineage leading to human. An alternative explanation is that the StSat repeats in chimpanzee and
gorilla have different origins and the repeats did not occur in human. The purpose of the present study was quantitative evaluation
of the above alternative possibilities by analyzing the nucleotide variation contained in the repeats. We collected large
numbers of sequences of repeat units from genome sequence databases of chimpanzee and gorilla, and also bonobo (an African
great ape phylogenetically closer to chimpanzee). We then compared the base composition of the repeat units among the 3 species,
and found statistically significant similarities in the base composition. These results support the view that the StSat repeats
had already formed multiple arrays in the common ancestor of African great apes. It is thus suggested that humans lost StSat
repeats which had once grown to multiple arrays. 相似文献
18.
The internal transcribed spacer (ITS) regions of 18–26S nuclear ribosomal DNA was sequenced to address phylogenetic relationships
and to measure the extent of differentiation among six species of the Far EasternIndigofera. ITS 1 had 230–240 base pairs (bp) long while ITS 2 had 211–213 bp long. The 5.8S rRNA coding region was 161 bp long. Sequence
divergence calculated by Kimura's two parameter method between species ranged from 0.00 to 13.49%. A single most parsimonious
tree was produced from 77 variable nucleotide sites, which had a consistency index of 0.97 and a retention index of 0.83.
ITS sequence data suggested that the continental species ofI. kirilowii (2n=16) is diverged from the common ancestor of other species at first, and then the island species ofI. decora (2n=48) andI. venulosa and the Korean Peninsular species ofI. grandiflora (2n=16) andI. koreana (2n=32) are diverged from the ancestor. The molecular data supports that the speciation in the Far EasternIndigofera occurred with polyploidization from continental ancestor to peripheral peninsular and island species. 相似文献
19.
Whereas examples of insular speciation within the endemic-rich Macaronesian hotspot flora have been documented, the phylogeography of recently evolved plants in the region has received little attention. The Macaronesian red fescues constitute a narrow and recent radiation of four closely related diploid species distributed in the Canary Islands (F. agustinii), Madeira (F. jubata), and the Azores (F. francoi and F. petraea), with a single extant relative distributed in mainland southwest Europe (F. rivularis). Bayesian structure and priority consensus tree approaches and population spatial correlations between genetic, geographical, and dispersal distances were used to elucidate the phylogeographical patterns of these grasses. Independent versus related origins and dispersal versus isolation by distance (IBD) hypotheses were tested to explain the genetic differentiation of species and populations, respectively. Genetic structure was found to be geographically distributed among the archipelagos and the islands endemics. The high number of shared AFLP fragments in all four species suggests a recent single origin from a continental Pliocene ancestor. However, the strong allelic structure detected among the Canarian, Madeiran, and Azorean endemics and the significant standardized residual values obtained from structured Bayesian analysis for pairwise related origin hypotheses strongly supported the existence of three independent continental-oceanic colonization events. The Canarian F. agustinii, the Madeiran F. jubata, and the two sister F. francoi and F. petraea Azorean species likely evolved from different continental founders in their respective archipelagos. Despite the short span of time elapsed since colonization, the two sympatric Azorean species probably diverged in situ, following ecological adaptation, from a common ancestor that arrived from the near mainland. Simple dispersal hypotheses explained most of the genetic variation at the species level better than IBD models. The optimal dispersal model for F. agustinii was a bidirectional centripetal stepping-stone colonization pattern, an eastern-to-western volcanism-associated dispersion was favored for F. francoi, whereas for the recently derived F. petraea a counterintuitive direction of colonization (west-to-east) was suggested. The population-based phylogeographical trends deduced from our study could be used as predictive models for other Macaronesian plant endemics with similar distribution areas and dispersal abilities. 相似文献
20.
Moriyama Hiromitsu Horiuchi Hideki Nitta Takeshi Fukuhara Toshiyuki 《Plant molecular biology》1999,39(6):1127-1136
Endogenous, 14 kb double-stranded RNAs (dsRNAs) have been found in two ecospecies of cultivated rice (temperate japonica rice and tropical japonica rice, Oryza sativa L.) and in wild rice (O. rufipogon, an ancestor of O. sativa). A comparison of the nucleotide and deduced amino acid sequences of the core regions of the RNA-dependent RNA polymerase domains found in these three dsRNAs suggested that these dsRNAs probably evolved independently within each host plant from a common ancestor. These dsRNAs were introduced into F1 hybrids by crossing cultivated rice and wild rice. Unusual cytoplasmic inheritance of these dsRNAs was observed in some F1 hybrids; the evolutionarily related dsRNAs were incompatible for each other, and the resident dsRNA of an egg cell from cultivated rice was excluded by the incoming dsRNA of a pollen cell from wild rice. Coexisting dsRNAs in the F1 hybrids segregated away from each other in the F2 plants. However, the total amount of these dsRNAs in the host cells remained constant (ca. 100 copies/cell). The stringent regulation of the dsRNA copy number may be responsible for their unusual inheritance. 相似文献