| Liriodendron sino-americanum has many advantages,such as tall tree,peculiar leaf shape,gorgeous colors,fast-growing and high yield,high timber yield,strong stress resistance and so on.It is not only actively promoted in the landscaping of many cities,but also paid attention to the cultivation of timber forest in the hills and mountains in recent years.Compared with their parents(Liriodendron chinense(Hemsl.)Sarg.and Liriodendron tulipifera L.),they have an obvious advantage of height growth,especially compared with L.chinense.As one of the important biological characters of trees,controlling height growth can make people obtain obvious economic and environmental benefits in tree cultivation or horticulture.Therefore,it has theoretical and practical significance to study the cause of the difference of height growth between L.chinense and L.tulipifera.Based on high-throughput sequencing technology,this study preliminarily explored the mechanism of the difference of height growth from the molecular level by using the apical buds of the trunks of L.chinense and L.tulipifera as materials.The main results were as follows:(1)Based on microsatellite markers,the genetic diversity(gene heterozygosity)of L.sino-americanum(LH)(18 samples)and L.chinense(LC)(18 sample)was analyzed.It was found that the genetic diversity(gene heterozygosity)of LH was significantly higher than that of LC.The heterozygous characteristics of LH samples were common at multiple loci,while homozygotes were dominant in LC.The results showed that there were significant genetic differences between the two groups.(2)A total of 18 samples from three developmental stages(dormancy,germination and fast-growing)of LH and were sequenced and analyzed.A total of 130.84 g clean data were obtained.39053 unigenes with a length of 201-15915 bp and a N50 of 1643 BP were obtained by de novo assembly.24203(61.97%),23359(59.81%),21006(53.79%),18844(48.25%),17446(44.67%)and 11842(30.32%)unigenes were annotated in six databases(NR,eggnog,go,Pfam,Swiss prot,KEGG),respectively.(3)A large number of genes were differentially expressed in the apical bud of LH and LC at different stages of interspecific and intraspecific.At the same time,unigene was differentially expressed in dormant stage(LH1＿vs＿LC1),There were 3248 unigenes(1537 up-regulated and 1711 down regulated)in total.There were 4033 unigenes(2245 up-regulated and 1788 down regulated)in germination stage(LH2＿vs＿LC2).There was 3061 unigenes(1419 up-regulated and 1642 down regulated)in fast-growing stage(LH3＿vs＿LC3).The number of differentially expressed genes was the most in germinating stage.Comparison of three periods within species,There were 14127 differentially expressed genes in LH1＿vs＿LH2＿vs＿LH3,and 16705 in LC1＿vs＿LC2＿vs＿LC3.(4)Go enrichment analysis of differentially expressed genes revealed that extracellular domain,transcription factor activity,sequence specific DNA binding,cell wall,secondary metabolite biosynthesis,plant cell wall and other pathways related to cell morphogenesis and cell wall synthesis were significantly enriched.In KEGG enrichment analysis,plant hormone signal transduction and starch and sucrose metabolic pathways were significantly enriched.This is in line with expectations.Plant hormone signaling pathway is responsible for regulating the expression of plant hormones to control cell growth,while starch and sucrose metabolic pathways provide energy for cell activity.(5)The results of go enrichment analysis showed that the third and fourth genes groups(up-regulated in fast-growing stage)were mainly related to cell wall formation and photosynthetic reaction,while genetic material preparation and hormone signal transduction were mainly in five and six categories(on germination stage).The difference of cell division mediated by hormone related genes may be one of the reasons for the difference of height growth between LH and LC.(6)Based on the important role of hormone regulatory genes in plant growth,the expression profile of plant hormone signal transduction related genes was analyzed.It was found that the expression levels of IAA16,GH3.1,CYCD4-1,etc.related to plant hormone signal transduction regulating cell enlargement and division were significantly different between species at fast-growing or germination stage,which may be caused by plant hormone signal transduction pathway.These genes are important genes for the difference of height growth between LH and LC.(7)Except for BR in germination stage and ABA in fast-growing stage,the contents of five endogenous hormones in LH were higher than those in LC,and the ratio of endogenous hormones in dormant stage and germination stage was higher than that in fast-growing stage.Based on the analysis of the expression of key enzyme genes in IAA,ZR,BR and ABA synthesis pathway,it was found that the changes of expression of YUC9,CYP90D2,NCED1 and other genes in different stages may be significantly related to the changes of their corresponding hormone content,indicating that they play an important role in regulating hormone synthesis during the growth and development of apical bud of Liriodendron. |
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