Excellent Gene Mining Related To Flower Bud Differentiation In Summmer Flowering Chrysanthemum And Response To Low Temperature In Chrysanthemum Nankingense

Chrysanthemum(Chrysanthemum morifolium),as one of the ten most famous flowers in China and one of the four most popular cut flowers over the world,provides high ornamental and economic value.However,most chrysanthemum cultivars are obligate short-day plants in China,and bloom mainly in autumn.It has affected the yeard-round production and application due to the relative short and concentrated flowering.The nature flowering time of chrysanthemum ’Yuuka’ is from July to September,and widely popular due to its flower colour,shape,form,lasting flowering and most importantly,the tolerance to high temperature.Previous studies showed that the flowering chracteristics of ’Yuuka’was different from day-neutral chrysanthemum whose flowering was not regulated by day-length,and ’Yuuka’ flowered rapidly in SD(short day)and showed delays in LD(long day)since they came into photoperiod sensitive phase.To date,several reports involved in regulating time to flowering focused in autumn flowering chrysanthemum,and the molecular mechanisms of summer flowering chrysanthemum has not been reported yet.Besides,low temperature stress is becoming the bottleneck for restricting the chrysanthemum production development.Extreme low temperature in early spring and winter,unusual freezing temperature during late cold spring,and sudden frosts in fall often lead to growth arrest and block flower buds or inflorescence,especially the reproductive phase is often highly sensitive to cold stresses.Therefore,to obtain chrysanthemum varieties endowed with a heightened tolerance to low temperature stress is very important.C.nankingense has been considered as a convenient genomic model of hexaploid ornamental chrysanthemun due to its simple diploid nature.In addition,it displays better tolerance to low temperature as compared to the ornamental polyploid species.Temperate plant species can improve their freezing tolerance through the process of cold acclimation(CA).However,the molecular basis of CA and low temperature/freezing tolerance in chrysanthemum has not yet been explored.In response to the above scientific questions,this paper carried out some researches,based on the needs of chrysanthemum industry,and the main contents and conclusions are as follows:1.The transcriptome of flower bud differentiation in summer flowering chrysanthemum ’Yuka’ both under relative short day length and mock long day length was acquired through the next generation sequencing technology based on Illumina HiSeqTM 2000 platform.The results showed that photoperiod pathway and gibberellin pathway accelerate flowering together under the relative short photoperiod,while under the mock long photoperiod,due to the up-regulated expression of Unigenes encoding trehalose-6-phosphate synthase and sucrose synthase,trehalose-6-phosphate and synthase signaling accelerate the flowering,while the up-regulated expression of PHYB which block flowering in photoperiod pathway,were responsible for ’Yuka’ flowering rapidly in SD and showing delays in LD.2.The transcriptomic response to low temperature by comparing different transcriptome of Chrysanthemum nankingense plants subjected to a period of sub-zero temperature(-5℃),with or without a prior low temperature acclimation was characterized and analyzed based on RNA-Seq platform.The results showed that Ca2+-dependent signaling pathway,dehydrin and LEA play the crucial role in responsing to freezing temperature through low temperature acclimation,while MAPK pathway were more strongly involved in the response to freezing directly.Furthermore,six major TF classes(AP2/ERF,bHLH,WRKY,TCP and MYB)were identified as DTGs in the treatments involved in a process of low temperature acclimation.Moreover,DEAD-box RHs involed in post-transcriptional RNA metabolism were activated during the process of low temperature acclimation.In addition,HSPs were also identified as the DTGs in treatments involving low temperature response.3.BBX proteins have been demonstrated to play vital roles in regulating flowering time and response to abiotic stresses.Here,we reported the isolation of 12 BBX transcription factors from chrysanthemum ’Yuuka’,and compared these identified amino acid sequence with their orthologs in model plant Arabidopsis.The result showed that all the twelve BBX transcription factors were classified into three groups.The expression pattern of CmBBX showed difference in various tissues.The expression pattern of flower bud differentiation under different photoperiod provided the evidence that CmBBX15.2 and CmBBX20 showed up-regulated,while CmBBX22.1 showed down-regulated under relative short day length;Besides,CmBBX15.1 was inhibited at first and then enhanced.Furthermore,the expression pattern of low temperature treatment showed that CmBBX19 and CmBBX22.2 were obviously enhanced.Moreover,the expression pattern of NaCl treatment showed that CmBBX7.1,7.2,8,21 and 22.2 were obviously enhanced,and CmBBX7.1,8,20 and 22.2 were significantly up-regulated under the treatment of abscisic acid treatment.In addition,the results of determination of the subcellular localization of the identified 9 chrysanthemum BBX proteins showed that they were all localized to the nucleus in onion epidermal cells,while CmBBX 19 was both localized to the nuleus and on the cell membrane.The results of transcriptional activities of the identified 9 chrysanthemum BBX proteins suggested that no transcription activation of CmBBX 15.1 was found in yeast cell,while the other eight CmBBX showed great ranscription activation.