| Camellia yuhsienensis H.H.Hu belongs to the Camellia L family of Theaceae and it is a unique woody oil tree species in China.The flowering period of C.yuhsienensis is from March every year,which can effectively avoid the influence of low temperature,rainy and frosty weather in south China on the pollination and fertilization of C.oleifera.Pollination and fertilization are closely related to fruit setting of C.oleifera,which affects the fruit yield of C.oleifera.Analyzing the developmental process and physiological regulation mechanism of C.oleifera in different flowering times has become one of the key issues to improve its output.This study remote the specific germplasm of C.yuhsienensis ’Autumn flowers No.1’(First flowering begins at the end of November)and the ’Spring Flower No.3’(The first flowering begins at the next year in early March)as test materials,from the morphology,cytology,physiological and biochemical,transcriptome study the four aspects to compare Flower development process,endogenous hormone and nutrient content changes about two types of the C.oleifera flowering times and screen related signaling pathways and key genes.Aims to provide scientific basis for the regulation of C.oleifera flowering period,The main research conclusions are as follows:1.There was no significant difference in flower development and internal microstructure of C.yuhsienensis among different flowering stages.Combining morphological and cytological analysis,it founds that the flower development progress of ’Autumn flowers No.1’ and ’Spring Flower No.3’ is similar.Both flower buds morphological differentiation started in mid to late May and was completed in mid to late August,and then entered the stages of megaspore differentiation and male and female gametophyte differentiation.Finally completed flower bud differentiation in late November.The result indicating that there was no difference in the internal microstructure of the two flower buds during their differentiation,so which might be caused by different endogenous physiological or molecular mechanisms.2.GA3,IAA and CTK promoted the morphological differentiation of C.yuhsienensis flower buds,and CTK caused the difference of flowering period between ’Autumn flowers No.1’and ’Spring Flower No.3’.At the stage of flower bud morphological differentiation,the contents of GA3,IAA and CTK in flower buds of ’Autumn flowers No.1’ and ’Spring Flower No.3’ were significantly up-regulated,which illustrate that these three hormones were positively correlated with the flower bud morphological differentiation of the two.At the stage of male and female gametophyte differentiation,the contents of GA3,ABA,CTK,and BR in ’Autumn flowers No.1’ and ’ Spring Flower No.3’ were noteworthy down-regulated,showing that they may be negatively correlated with gametophyte development.The CTK content in flower buds was conspicuous higher than that of ’Spring Flower No.3’,which was 193.11%of that of ’Spring Flower No.3’.When the ’Autumn flowers No.1’ bloom,the CTK content of the two flower buds exists significant difference,suggesting that CTK might be related to the difference in flowering stage between the two flowers.3.The accumulation of sugars was beneficial to the development of C.yuhsienensis.During the process of flower development,the contents of soluble sugar,sucrose and starch in the flower buds of ’Autumn flowers No.1’ and ’Spring Flower No.3’ shows a significant upward trend.Among them,the accumulation of soluble sugar in flower buds of ’Autumn flowers No.1’ is mainly concentrated in the differentiation stage of sporophyte and gametophyte,while that of ’Spring Flower No.3’is mainly concentrated in the stage of morphological differentiation of flower buds;The accumulation of starch in flower buds of ’Autumn flowers No.1’ and ’Spring Flower No.3’ mainly occurred from the differentiation stage of megaspore to the differentiation stage of male and female gametophytes.the starch content was twice that of the stage of morphological differentiation.Indicating that the accumulation of carbohydrates is the material guarantee for the development of C.yuhsienensis.4.Zeatin synthesis and signal transduction were key pathways leading to the difference in flowering time between’Autumn flowers No.1’ and’Spring Flower No.3’.A total of 13 456 differentially expressed genes(DEGs)were screened in the five developmental stages of’Autumn Flower No.1’ and ’Spring Flower No.3’.Before flowering,the number of DEGs in QS9 vs CS9 was the largest(5618).Among them the number of up-regulated genes was 2898 and the number of down-regulated genes was 2720,reaching the maximum in all five comparison groups.Indicating that the S9 stage(the late stage of male and female gametophyte differentiation)is a critical period when the physiological and biochemical metabolic activities of ’Autumn Flower No.1’ and’Spring Flower No.3’ are quite different.The KEGG(Kyoto Encyclopedia of Genes and Genomes)biological pathway enrichment of 13 456 differentially expressed genes showed that the above differentially expressed genes were significantly enriched in flavonoid biosynthesis,phenylpropane biosynthesis,plant hormone signal transduction,MAPK Signaling pathways-pathways in plants,starch and sucrose metabolism,zeatin biosynthesis,etc.Combined with the determination results of endogenous hormones in the flower buds of ’Autumn Flower No.1’ and ’Spring Flower No.3’,it is speculated that the synthesis and signal transduction pathways of zeatin are the key pathways that affect the difference of flowering period between ’Autumn Flower No.1’ and ’Spring Flower No.3’.5.Low levels of endogenous cytokinin may caused differences in flowering period between ’Autumn flowers No.1’ and ’Spring Flower No.3’.In the zeatin synthesis and signal transduction pathway,a total of 46 differentially expressed genes were screened,Among them,the number of differentially expressed genes in S9(late stage of male and female gametophyte differentiation)and S10(flowering of ’Autumn Flower No.1’)accounted for 63.04%of the above differentially expressed genes.These different-expressed genes mainly include UGT,7-deoxyloganetin glucosyltransferase,UGT,UDP-glycosyltransferas,ZOG,Zeatin O-glucosyltransferase,CKX,Cytokinin dehydrogenase,AHK,Histidine kinase,AHP,Histidine-containing Phosphotransfer protein,ARR&BRR,two-component response regulator,etc.According to the analysis of the expression patterns of the above differentially expressed genes during flower development,it was found that the expression levels of CKX6,UGT8524-1 and UGT85A24-2 in ’Autumn Flower No.1’ were significantly up-regulated at S9,and the differentially expressed levels were most significant at S10.The up-regulated expression levels of the above genes may be the main reason for the decrease of cytokinin levels in ’Autumn Flower No.1’.Combined with the results of previous studies,it was speculated that the low level of endogenous cytokinin may be the main reason for the difference in flowering period between the two.The results showed that the flower development process was not the cause of the flowering difference between ’Autumn Flower No.1’ and ’Spring Flower No.3’,and the level of CTK might be the key point of the flowering difference. |
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