Identification And Regulation Of UGT Gene Family Members Related To Glycosylated Linalool Formation In Peach Fruit

Volatile compounds are presented in fruits as both free and bound forms.Bound volatiles are non-volatile and known as glycosylated volatiles.Formation of glycosylated volatiles is catalyzed by UDP-glycosyltransferase(UGT).As an important aromatic compound,linalool contributes to aroma quality of fruits such as peach.Understanding the formation of glycosylated linalool is of great significance for revealing mechanism of aroma quality and then to improve fruit quality.In the present study,peach fruit is used to investigate the identification and regulation of UGT genes responsible for glycosylated linalool production.The main results are as follows:1.A total of 168 peach UGT gene family members were identified by using the PSPG-box domain of plant UGT gene family.According to the phylogenetic tree cluster analysis,these peach UGTs were divided into 16 groups,of which G group is the largest(34 UGTs).UGT gene family members in peach were unevenly distributed on 8 chromosomes.A total of 96 peach UGT genes contained intron sequences,of which I-5(intron 5)was highly conservative.UGT gene family members had different expression patterns in different tissues and peach fruit developmental stages using the RNA-seq.UV-B treatment induced expression levels of 65 UGTs(39%)and inhibited transcript levels of 24 UGT gene family members(14%).2.A total of 26 glycosylated volatiles were identified from peach fruit.Glycosylated linalool was the most abundant glycosylated terpenoid volatiles.In peach fruits,30%linalool were presented as glycosylated form.Content of glycosylated linalool were increased with peach fruit ripening,and were induced by exogenous ethylene treatment.UV-B irradiation significantly inhibited glycosylated linalool accumulation.3.Peach PpUGT85A2 was associated with the biosynthesis of glycosylated linalool.Correlation analysis revealed that transcript levels of PpUGT85A2 was positively correlated with content of glycosylated linalool between peach cultivars,during fruit ripening,in response to treatments such as ethylene,salicylic acid and UV-B treatments.Application of free linalool significant induced expression of PpUGT85A2 and content of glycosylated linalool in peach leaves.Recombinant protein PpUGT85A2 catalyzed production of glycosylated linalool in vitro using UDP-glucose as sugar donor and linalool as substrate.Transient overexpression in peach fruits and stable overexpression in Arabidopsis and tobacco resulted in significant accumulation of glycosylated linalool in vivo.4.Transcription factor PpNAC8 could activate PpUGT85A2 transctiption in planta.Transcription factors gene expression during peach fruit ripening was analyzed using RNA-seq,and transcripts correlated with glycosylated linalool was selected as candidates for further analysis,including NAC,WRKY and ERF gene family members.Dual-luciferase assays indicated that PpNAC8 could trans-activate the PpUGT85A2 promoter.These results indicate that formation of glycosylated linalool during peach fruit ripening could be transcriptional regulated.