Identification of Floral Components and Functional Analysis of Key TPS Genes in Syringa oblata
Terpene synthase(TPS)gene is a key regulator gene in the biosynthesis pathway of terpenoids,playing a crucial role in plant terpene metabolism.In this study,the floral fragrance components of lilac petals at different flower development stages(including bud stage,beginning stage,blooming stage and withering stage)were identified and analyzed on the basis of optimizing the floral conditions of headspace solid-phase microextraction(HS-SPME).The key candidate genes of SoTPS2 and SoTPS3 were identified by combining genome and transcriptome data,and their isolation and preliminary functional investigation were carried out.The results showed that:(1)The optimal extraction condition was 30 ℃ for 40 min by analyzing the difference of types and release amount of volatile compounds under different extraction temperature and time.The total release of floral fragrance showed a trend of first increasing and then decreasing during the four flower development stages,and the peak(highest level)was observed at full flowering stage.Terpene compounds accounted for the highest proportion in total of floral compoents in the four periods,and the monoterpene ocimene was the highest.(2)The open reading frames(ORF)of SoTPS2 and SoTPS3 genes were 1731 bp and 1779 bp,respectively,encoding 576 and 592 amino acids.The deduced proteins have Terpene_Cyclase_Plant_C1 conservative structural domain,belonging to Isoprenoid_Biosyn_C1 superfamily.The highest transcripts of the two genes were detected in the petals via real-time PCR,and the increased expression was first detected followed by a decrease along with the flower development stages.The gene expressions positively correlated with the release of ocimene.(3)Through the transient overexpression of SoTPS2 and SoTPS3 genes in the petals of Antirrhinum majus,we observed 10.91 and 23.67-fold increased on the release of ocimene,respectively,compared with the unoverexpressed group.Collectively,the main components of floral fragrance in lilac petals are monoterpenes,and SoTPS2 and SoTPS3 as downstream regulating genes can contribute the synthesis of monoterpenes,especially ocimene.
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