| Crape myrtles are important woody plants with summer flowering in China.Flower scent is a hot issue in crape myrtle breeding while there are few aroma cultivars in Lagerstroemia.L.caudata is a significant source of aromatic species in Lagerstroemia with monoterpenoids as one of its major categories of volatiles.Until now,the characteristic aroma volatiles of L.caudata and its temporal-spatical emission patterns had not yet been determined.Besides,key genes and TFs related to the MEP pathway had not been well studied too,lacking of relevant biological data.Therefore,it is difficult to make efficient application of L.caudata.In this study,phenotypic observation,HS-SPME-GC-MS,quantitative with external standards coupled with transcriptomics and metabolomics were used to determine the main aroma volatiles,emission rhythm and key floral gene.The results were given as follows:(1)Flower extracts of L.caudata were affected by the extraction parameters of SPME.A4B3C2D4E1,namely sample weight 0.4 g,a 50/30 μm DVB/CAR/PDMS-2 cm fiber,40 min of extraction time at 50℃,2 min of desorption time was selected as the optimum pre-treatment conditions of SPME sampling.A total of 29 floral volatiles was identified in single flowers(6:00 am)of L.caudata.Among them,20 volatiles were first detected in L.caudata.Aliphatic alcohols(48.79%)and monoterpenoids(38.22%)were the main volatiles catagories while the relative content was varied.(2)The cmission of floral volatiles varied in different flower development stages of L.caudata.The total emission amounts of volatiles were much higher in full blooming stage(140.90 ng/g/min),comparing with in squaring stage(36.54 ng/g/min)and in last flowering stage(24.92 ng/g/min).Monoterpenoids were the characteristic feature to distinguish these three stages.Among them,nerol,geraniol and linalool with sweet and flower aroma had the most emission level.The release of volatiles,especially the monotepenoids in L.caudata varied over a day,presenting apparently a diurnal scent emission pattern.6:00 am was the best pollination time point.(3)Volatiles release of L.caudata showed a certain spatial difference.Stamen emitted the most amounts,627.96 ng/g/min,comparing with petal,pistil,calyx and pedicel(6.02-69.74 ng/g/min)and was regarded as a significant source of floral volatiles in L.caudata.The scent composition based on the relative amounts varied greatly witlin flowers.Stamen was characterized by high levels of aliphatic alcohols and monoterpenoids,which is similar to the presence of the whole flower.Floral volatiles’variation in tissue-specific was also observed.For example,nerol and linalool were detected respectively only in stamen and pistil.(4)Sixteen significant differential metabolites were identified from flowers of L.caudata in squaring stage,full blooming stage and last flowering stage,including 7 monoterpenoids,4 aliphatic alcohols,3 aliphatic aldehydes and 2 benzenoids.Among them,the emission patterns of 6 monoterpenoids such as nerol,geraniol,linalool,citronellol,citral and geranial were consistent with the variations of floral phenotypic space of L.caudata.The major metabolic pathway involved in was geraniol degration.Key genes involved in the pathway were selected by RNA-seq and their expression patterns were studied.Finally,a hypothetical model of MEP pathway of L.caudata was proposed.This study described the feature of volatiles constitutions and temporal-spacial release rhythm in L.caudata and explored its molecular regulation mechanisms.These results obtained increased our understanding of the aroma volatiles in Lagerstroemia and provided a theoretical support for the efficient utilization of fragrant Lagerstroemia species and the targeted breeding of new Lagerstroemia varieties with desirable floral scents. |
PDF Full Text Request