Morphological Observation And Transcriptome Analysis Of Flower Bud Differentiation Of Magnolia

Magnolia are widely cultivated for their beautiful flowers,but despite their popularity,the bud differentiation process and molecular mechanisms regulating flower bud differentiation have not been elucidated.In this study,the process of flower bud differentiation of M.biondii,M.denudata,M.× soulangeana ‘Red lucky' and M.sinostellata was observed,and the paraffin sections and RNA-seq were used to study the process of flower bud differentiation in M.sinostellata.All results were showed as following:(1)Flower bud development of four species occurred between April and early June.M.denudata,M.× soulangeana ‘Red lucky' and M.sinostellata flower bud differentiation were divided into five stages: undifferentiated stage,early stage of flower bud differentiation,flower petal primordium differentiation stage,stamen primordium differentiation stage and pistil primordium differentiation stage.M.biondii was divided into six stages: undifferentiated stage,early stage of flower bud differentiation,sepal primordium differentiation stage,petal primordium differentiation stage,stamen primordium differentiation stage and pistil primordium differentiation stage.During flower bud differentiation,there were no difference among four species.The flower bud primordium of four species started to grow and widen at first stage,then multiple rounds of raised dots appeared gradually from the outside to the inside,and the flower organ primordia were completed finally.The stamen primordium and the pistil primordium were arranged on the growth cone,and each base of the primordium appeared almost at the same time.(2)A total of 52,441 expressed genes were identified by transcriptome data,of which 11592 were significantly differentially expressed in the five bud development stages(FDR<0.05)of M.sinostellata.A gene ontology(GO)enrichment analysis of the DEGs revealed a significant enrichment of 371 GO terms throughout the differentiation process(P < 0.05).The DEGs were successfully annotated as members of 241 pathways and the number of significantly enriched KEGG pathways was 36(P < 0.05).(3)82 related to the flowering of M.sinostellata were involved in six pathways of flowering transformation during flower bud differentiation.Form first stage to last stage CRY expression in the photoperiod pathway decreasing increased the expression of GI and CO,which promoted flowering finally.The expression of FY,FPA,and FRI in the autonomic pathway and vernalizationpathway,LFY gene in the gibberellin signal,SPLs genes participate in flowering autonomous pathways were increased.In addition,MADS-box and AP2 family genes plaied critical roles in the formation of flower organs and 20 DEGs associated with flower bud differentiation were identified in M.sinostellata.A q RT-PCR analysis verified that the MADS-box and AP2 family genes were expressed at high levels during flower bud differentiation.