| Leymus, one of the perennial genus of Triticeae, Poaceae, distributed widelyin frigid-temperate zone of the Northern Hemisphere. Most of the materials ofLeymus possess the characters such as chilliness and drought-resistance,saline-tolerance, disease and insect pests resistance, so it is one of the importantgene sources for wheat improvement. In this paper, we investigated and collectedthe populations of L. secalinus from North-western area of China, which is one ofthe widely distributed species of Leymus in China. The spike morphology andseed set traits of 19 populations collected from Qinghai province wereinvestigated. And the genetic diversity of 28 populations from North-western areaof China was evaluated by means of two molecular marker systems, genomic-SSRand EST-SSR. To identify the parental Psathyrostachys ancestries which offeredthe Ns genome to Leymus and to elucidate the origins of another base genome ofLeymus we cloned and sequenced two chloroplast genes and two nuclear genes ofeight species of Leymus (L. angustus, L. chinensis, L. paboanus, L. racemosus, L.karelinii, L. sabulosus, L. mollis and L. secalinus) and compared these sequenceswith the homologous genes of Psathyrostachys and other Triticeae species. Themajor results of this study are as follows:1, L. secalinus distributed unevenly on the whole with more populationsdistributing in the areas of Gonghe county and Heka districts of Xinghai county inthe eastern region of Qinghai as well as the southern area of Doulan county in themiddle region of the province. The growth of L. secalinus was disturbed often byhuman activities and influenced by the accessibility of water. In allmorphological characteristics investigated, the nodosity length varied greaterthan other traits investigated with a coefficient of variance (CV) of 26.2%,followed by awn length (CV 23.1%). The glume length had the minimalcoefficient of variance of 8.7%. Pairs of populations were not necessarily clustertogether according to the geographical locations. On the contrary, somepopulations distributed in the similar ecological environment were clusteredtogether first. Populations with low seed set were in the majority and the meanpercentage seed set was only 22.5%. But one population, Z2618, had a higherseed setting up to 63.7%. And we found that the seed setting of L. secalinus wascorrelative with population size to some extent.2, After screening 384 pairs of primers (including genomic-SSR andEST-SSR) from wheat, barley and rye genomes 74 primer pairs were found to beable to amplify clear and reproducible product from L. secalinus genomic DNA with a transferable rate of 19.3ï¼…. 21 primer pairs selected in this study amplifieda total of 327 alleles in 28 populations (30 individual plants per population) withan average of 15.6 alleles detected by one primer pair. Thereinto, 10genomic-SSR and 11 EST-SSR primer pairs detected 232 and 95 allelesrespectively. The mean number of alleles detected by one primer pair was 23.2 forgenomic-SSR and 8.6 for EST-SSR. The genetic diversity index for allpopulations was 0.760 with a value of 0.647 from intra-population and 0.112 fromamong-population. The population differentiation coefficient was 0.148 whichindicted that there was 14.8ï¼…genetic diversity among populations and 85.2ï¼…between individual plants in population.The percent of polymorphic loci ranged from 90.5ï¼…to 100ï¼…and 22populations, were polymorphic at all loci analyzed. The mean number of allelesand genetic diversity index detected for each population varied from 3.4 to 7.7and 0.530 to 0.718 respectively. The alleles per loci, the percent of polymorphicloci and the mean genetic diversity index of 18 populations from Qinghai Plateauwere 6.5, 99.7ï¼…, and 0.672, respectively, higher than which of 7 populations fromHuangtu Plateau (5.3, 96.6ï¼…, 0.618) and 3 populations from Xinjiang (4.7, 93.7ï¼…,0.567), respectively.The efficiency of genomic-SSR to detect the genetic diversity was higherthan which of EST-SSR, in other words, for most primers, genomic-SSR coulddetect more genetic variance than EST-SSR. And on the whole, there wascorrelativity between the value of genetic variance detected by genomic-SSR andwitch detected by EST-SSR, that is, for most populations of L. secalinus, thehigher the value of genetic variance detected by genomic-SSR, the higher thevalue detected by EST-SSR.The genetic diversity of populations which had seed set no more than 20ï¼…was lower distinctly than that of the populations having seed set higher than 20ï¼….This indicated that the deficiency of genetic diversity was an important factorswhich could influence the seed set of populations of L. secalinus. However,Z2428, one population from Xinjiang, had the lowest genetic diversity and thehighest seed set of 76.6ï¼…in all 28 populations analyzed. This population mayhave different breeding system. Taking into account of the population size data, itcould be found that preponderant populations or populations growing indenseness had usually higher genetic variance and seed set.3, Comparative phylogenetic analysis of two chloroplast genes, rpoA andrbcL, between species of Leymus, Psathyrostachys and other Triticeae genus, itcould be found that the chloroplast genome of 8 Leymus species arose from thegenus Psathyrostachys. And Ps. fragilis, Ps. caduca, Ps. rupestris and Ps. huashanica were not the parental ancestor which offered the Leymus chloroplastgenome. Ps. juneca and/or other species which had close phylogeneticrelationship with Ps. juneca may be the mother parental ancestor of Leymusspecies. Phylogenetic analysis of partial nuclear gene, DMC1, indicated that Ps.fragilis was one of the parental ancestors who offered one of the Ns genomes to L.racemosus, L. mollis, L. karelinii and L. sabulosus. Another genome of L.racemosus, L. mollis, L. karelinii and one of the genomes of L. angustus may benot the Ns genome of Psathyrostachys and waxy genes showed that anothergenome of L. racemosus had close phylogenetic relationship with St genome. Twodistinct genomes of L. secalinus, L. paboanus and one of the genomes of L.chinensis may arise from Psathyrostachys, but this genome was different fromwhich of Ps. fragilis and Ps. juncea.Based on these results from this study, we can draw conclusions that: 1,Spike morphology traits of L. secalinus were associated close with habitatenvironment. The propagation and growth of L. secalinus were influenced byenvironmental conditions such as water accessibility and were disturbed often byhuman activities. As a whole, it is necessary to strengthen the protection of L.secalinus. 2, the population size of L. secalinus was correlative with geneticdiversity and seed set. 3, the mean genetic diversity of 18 populations fromQinghai province was higher than which of 7 populations from Huangtu Plateauand 3 populations from Southern area of Xinjiang. As for the conservationstrategy of L. secalinus, we can sample from such populations as Z2618 andZ2664 from the central area of Qinghai province and Z2167 and Z2115 fromHuangtu Plateau. 4, the chloroplast genome of 8 Leymus species arose from thegenus Psathyrostachys, but Ps. fragilis, Ps. caduca, Ps. rupestris and Ps.huashanica were not the maternal ancestor which offered the Leymus chloroplastgenome. Ps. fragilis was one of the parental ancestors who offered one of the Nsgenomes to L. racemosus, L. mollis, L. karelinii and L. sabulosus and anothergenome of L. racemosus had close phylogenetic relationship with St genome. Twodistinct genomes of L. secalinus, L. paboanus and one of the genomes of L.chinensis may arise from Psathyrostachys, but this genome was different fromwhich of Ps. fragilis and Ps. juncea. These suggested that Leymus species havemultiple origins, that is, the origins of the chloroplast and nuclear genomes ofLeymus species may be same or not same according to different species. |
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