| Fuji apple is the variety with the largest cultivated area and the highest yield in China.However,It has poor quality of flower bud,which seriously affects the fruit yield.In this paper,the cultivar ’Nagafu No.2’ was treated with 1.5% and 3% exogenous glucose in 25 days and 30 days separately after full bloom to study on its effects on flower bud initiation.RNA-seq was used to analyze the expression patterns on how exogenous glucose regulated floral genes;based on whole genome resequencing,we identified differences in DNA polymorphisms of related genes in the difficult flowering variety ’Nagafu No.2’ and easy initiation of floral bud variety ’Yanfu No.6’.Taken together,the physiological and molecular mechanisms of glucose influences in apple flower bud induction were analyzed.The main results we obtained are as follows:1.Glucose treatment promoted the accumulation of soluble sugar and starch content in terminal spur buds,and increased the length,width and fresh weight of buds during floral initiation,as well as flowering rate.However,the content of fructose in the phenotype of easy initiation of floral bud all decreased,indicating that the type and proportion of sugar had a certain influence on the floral differentiation of Fuji apple.2.Based on RNA-seq,exogenous glucose treatment significantly affected the sugar metabolism and expression patterns of flowering-related genes compared to control treatments.The number of differentially expressed genes at the three critical timing points of flower bud physiological differentiation was 9045,1959,and 6829,respectively.The number of up-regulated genes was 186 in all three periods,and the number of genes which were down-regulated was 426.The number of differentially expressed genes related to sugar metabolism and flowering related,which responsed to glucose treatment and played an important role in flowering induction of Fuji apple,was 34 and 27,respectively.3.Using the re-sequencing technology,whole genome re-sequencing was performed on ‘Nagafu No.2’ and ‘Yanfu No.6’,and the differences between the genome-wide DNA polymorphisms were analyzed and compared.(1)There were 5,409,757 and 5,149,354 SNPs identified in the cultivars ’Nagafu No.2’ and ’Yanfu No.6’ respectively;the SVs were 266,513 and 230,483 respectively;and the INDELs were 1,554,595 and 1,491,351 respectively.(2)The number of unique SNPs in ’Nagafu No.2’ was 2,381,987,in ’Yanfu No.6’ was 2,121,584.The same SNPs in two cultivars were 3,027,770.Based on the unique SNPs of the two cultivars,Fst,Pi and Tajimi’s D were used to perform the gene sliding window and the positive selection regions were selected.A total of 1963 differential genes were obtained from different database annotations.4.Through qRT-PCR,it was found that the T6 P signaling pathway which regulated flowering differed significantly both in the transcriptome level after glucose treatment and DNA level between varieties with different flowering characteristics.MdTPS in this pathway significantly up-regulated in phenotypes of easy initiation of floral bud.In addition,MdFLC as well as MdFT1,MdSOC1,MdAP1,and MdLFY all upregulated in response to glucose treatment.Taken together,a hypothetical model of gene regulatory network for exogenous glucose mediating apple flower bud gestation was proposed. |
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