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Studies on the Molecular Mechanism of Heterosis in Liriodendron Based on SSR Markers

Author: YaoJunXiu
Tutor: LiHuoGen
School: Nanjing Forestry University
Course: Tree Genetics and Breeding
Keywords: Liriodendron heterosis SSR genetic distance general heterozygosity specific heterozygosity association analysis
CLC: S792.21
Type: PhD thesis
Year: 2013
Downloads: 47
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Abstract


It has been proved that an obvious heterosis occurred in interspecific hybrid ofLiriodendron, while its genetic basis has not been clear yet. In this paper, the relationshipbetween the heterosis of growth and the genetic distance among mating parents and theheterozygosity of hybrids was explored based on the evaluation on both growth traits and SSRmarkers. Two batch of crossing combinations were taken as experimental populations, onecontains16interspecific hybrid combinations and their parental half-sibs and was establishedin2006at Jingdezhen, the other covers17interspecific hybrid combinations,7intraspecifichybrid combinations and their parental half-sibs in2010at Nanjing. Furthermore, theassociation between the growth traits of hybrid Liriodendron and SSR markers were analyzed.Meanwhile, the relationship between the number of SSR markers and the measurement ongenetic diversity was also explored. The main results are as follows:There were significant variation existing among combinations when analysing3-7aheight and DBH of16hybrid combinations at Jingdezhen trial site. Two combinations withfastest growth are S×M and H×M; while two combinations with slowest growth are L×C2andN1×H. Analysis of variance revealed significant variations of annual growth existing amongboth tree ages and combinations. Relatively large difference of heterosis among hybridcombinations was found by comparing the growth of hybrids with parental half-sibs. Not allthe hybrids showed heterosis,12hybrid combinations showed positive heterosis and4hybridcombinations showed negative heterosis. According to the analysis of variance, heterosischange on DBH and heigh was clear among mating combinations that the results reach ahighly significant leve(lP=0.0001,P=0.0001),while heterosis change on height and over BPHfor DBH of mating combinations was not clear among forest ages that the results did not reacha significant level(P=0.4432,P=0.0819,P=0.1615), however, heterosis change on over MPHfor DBH of mating combinations was clear among forest ages that the results reach a highlysignificant level(P=0.002).Based on the analysis of the parental genetic distance, relatively large genetic variationsamong parents were found with variation range of0.117~1.4at Jingdezhen. According toresults of correlation analysis, significant correlations were not found between the geneticdistance and the heterosis of growth(P=0.9504,P=0.9823,P=0.6422,P=0.4591).Furtherstudies showed that heterosis reached the maximum when the genetic distance was about1,heterosis showed downward trend with further increase of genetic distance. In order to verifythe above conclusions, the correlation of genetic distance and heterosis was analyzed with thesame molecular marker at Nanjing Qiaolin trial site,and similar conclusion was gotten,Parental genetic distance1could be used as indicator of parent selection.The general heterozygosity of hybrids were analyzed with the same molecular marker atJing dezhen, the range of the general heterozygosity of hybrids was0.6931~0.8278.The correlation of the general heterozygosity and heterosis did not reach a significant level(P=0.8252,P=0.8846,P=0.7513,P=0.7286);The special heterozygosity of hybrids wereanalyzed according to the results of association analysis, the range of the specialheterozygosity of hybrids was0.3741~0.8714. Furthermore, the correlation was analyzedbetween special heterozygosity of hybrids and heterosis,the results did not reach a significantlevel too(P=0.5694,P=0.716,P=0.447,P=0.5389),It can be deduced that heterozygosity ofhybrids is probably not the main reason for the formation of Liriodendron heterosis.LD among101pairs of markers was analyzed using Tassel3.0Software,we found thatstrong linkage disequilibrium between the40pairs of loci. Population structure of16hybridcombinations was also explored based on the results of LD screening, we found that8was thethe best analog clustering number,and calculated the probability of hybrid combinationoffspring which attributed to the subsets. Furthermore, association analysis was investigatedbetween7-year-old growth traits of16hybrid combinations at Jing dezhen and101pairs ofmolecular markers,the result showed that6markers associated with height trait and7markersassociated with DBH trait when the correlation between markers and traits was highlysignificant (P<0.01=, and the associated markers were consistent in addition to the691sitedid not associate with height trait, Further speculated that there may be a high correlationbetween the two traits, Further studies showed that the correlation of height and DBH reacheda highly significant level (r=0.9438, P=0.0001).EST sequences which corresponded to the associated markers were identified accordingto the correlation results,the result of sequence alignment showed that EST sequences of the4sites matched with sequences which came from NCBI,EST sequences of the3sites were notfound in the database,EST sequence of the2ndsite corresponded to sequence of chloroplastchaperone (copper companion) in Ricinus communis;EST sequence of the fifteenth No. sitecorresponded to sequence of snurportin-1in Arabidopsis thaliana;EST sequence of No.542site corresponded to sequence of histone H1in Populus trichocarpa;EST sequence of No.642site corresponded to sequence of tip growth defective in Arabidopsis thaliana; Further studiesshowed that TIP1was necessary to promote tip growth and cell growth,however, the aboverelated genes function needed to be verified in Liriodendron.The relationship between the number of SSR markers and the measurement on geneticdiversity was explored,SSR sites were rearranged in accordance with the number of allelesand effective alleles,considered five sites as a gradient based on the order, the metrics ofgenetic diversity (Na, Ne, I, Ho, Nei) were selected to analyze genetic diversity of hybridcombinations. Further studies showed that the genetic diversity of hybrid combinations wasstable when the number of loci was about20.

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CLC: > Agricultural Sciences > Forestry > Forest tree species > Broad-leaved trees > Liriodendron
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