Studies On Physiologic And Molecular Mechanism Of Blueberry Dormancy

Bud dormancy is a kind of temporarily halt phenomenon in life cycle of plants. Natural bud dormancy of deciduous fruit trees can resist low temperature environment in winter. Bud dormancy has great significance on conservation, propagation and agricultural production of species. In nature conditions, plants need to cultivate in low temperature for a certain time to break dormancy and germinate. Insufficient chilling will block bud germination and growth or lead to abnormal buds, which do have bad influence on fruit production. These will affect the fruit production seriously. Blueberry is a new fruit tree species with high economic value, but the regulation mechanism of bud dormancy is still unknown, therefore, cases of failure in variety introduction, low output, poor quality and lag in facility cultivation technique occurred frequently in blueberry production. These factors hinder the development of blueberry industry seriously.Blueberry floral buds were used as materials, this paper studied the changes of physiological properties and analyzed the variation of gene expression and DNA methylation level and model during dormancy and dormancy release process. This paper aimed to explore the physiological and molecular mechanism of buds dormancy and dormancy release in blueberry, find key regulation genes, and provide guidance for blueberry molecular breeding and dormancy regulation and facility cultivation. The main results were as follows:1. Physiological properties in floral buds of blueberry during dormancy process were varied regularly:the proline content showed a rising trend after an initial drop, the soluble sugar content and the POD activity continued to raise, the soluble protein content and SOD activity continued to decline during endodormancy. With the beginning of dormancy release, the soluble sugar and protein contents, the SOD activity increased, while the POD activity had a decreation.2. The levels of total DNA methylation （38.41%）, hemi-methylation （11.32%） and fully methylation （27.09%） were down-regulated in dormancy released buds. About 84.35% methylation loci varied during dormancy release when compared with dormancy, among which DNA demethylation loci were 243 with percentage of 40.03%, DNA hypermethylation loci were 185 with percentage of 30.48%.3. Based on RNA-seq technology, the endodormancy transcriptome library and dormancy released transcriptome library were built and the digital gene expression profiling of floral buds in different dormancy status were analyzed and compared. The results show that there were 935 genes identified as significant differentially expressed between dormancy bud and dormancy released bud. Among these genes,470 were up-regulated and 465 down-regulated in endodormancy bud. These genes are mainly involved in the photosynthesis, photosynthesis-antenna proteins, DNA replication, starch and sucrose metabolism metabolic pathway.4. Changes in expression quantities of two genes numbered Comp₈5212 （starch metabolic process gene） and Comp₇9163 （MADS-box gene） which expressed differently between dormant and dormancy released floral buds were calculated by quantitative PCR throughout the process of dormancy in 3 blueberry materials. The results showed that the relative expression value of two genes maintained at a low level before endodormancy and increased when enduring endodormancy, achieved to the peak before dormancy release, then decreased after dormancy release. It implied that these two genes might play an important role in the regulation of dormancy and dormancy release in blueberry bud.5. A dormancy-associated MADS-box gene VcDAMl was cloned from dormant buds of blueberry using RACE technology. The dynamic changes of VcDAM1 gene expression in the process of dormancy in floral buds were analyzed by quantitative PCR. The results showed that the relative transcript level of VcDAM1 increased dramatically during endodormancy period and decreased sharply after dormancy releasing. It indicated that VcDAM1 may have relation to regulating bud dormancy and dormancy releasing in blueberry.