Identification And Specific Expression Patterns In Flower Organs Of ABCG Genes Related To Floral Scent From Prunus Mume

Prunus mume has a unique floral scent feature that can volatilize a large amount of benzyl acetate into the air during flowering.At present,the efficient volatilization mechanism of P.mume floral scent components is still unclear.Although ABC transporters are involved in the transmembrane transport of various secondary metabolites,the transporters that selectively recognize benzenoids have not been elucidated.In this study,P.mume ’Caizhi Wufen’ was used as experimental material.Gas chromatography-mass spectrometry(GC-MS)was used to study the volatilization of key aromatic components in different parts of flowers.Morphological characteristics of key fragrance releasing parts of flowers were observed by stereoscope,optical microscope and scanning electron microscope.The PmABC gene family was identified by bioinformatics analysis.The RNA-seq was used to analyze the expression patterns of the ABCG gene in different parts of flower organs,and q RT-PCR was used to verify the expression pattern.Furthermore,the correlation between the volatilization of flowers and ABCG gene was analyzed.The main results are as follows:1.The flower organs were divided into five parts,which were petal,filament,anther,calyx and other.The volatile and endogenous components were analyzed by GC-MS in different parts of flower organs,and the analysis of qualitative and quantitative was carried out.Combined with the weight of different parts of flower organs,the proportions of the key aromatic components were analyzed in a single flower.The volatilization rate of the key components was further studied in different parts.The results showed that the contents of benzenoid were relatively higher in different parts of flower organs of P.mume,among which benzaldehyde,benzyl alcohol and benzyl acetate were the key aromatic components.The relative volatile and endogenous content of benzaldehyde was the highest in anthers.Petals were the heaviest in a single flower,and 90.32% of the endogenous content of benzyl alcohol came from petals.Filaments are the key fragrance-releasing parts of benzyl acetate.In a single flower,the weight of filament was only 11.77%,but the volatile amount of benzyl acetate was more than 70%.In terms of endogenous content,benzyl acetate was specifically stored in petals and anthers.Moreover,the volatilization rates of diverse aromatic components were different in several parts.And benzyl acetate had the highest volatilization efficiency in filament.2.The epidermal structure was observed by stereoscope,optical microscope and scanning electron microscope in flower organs of P.mume.The results showed that no specific glands were found in different parts of flowers.The structure of the adaxial and abaxial petal is similar,and the cells are closely arranged by irregular cells,and the cells are protruding outwards,and the cell surface has dense and regular curly stripes.There are oil cells on the surface of filament,and these oil cells may be closely related to floral volatilization.The anther epidermal cells are orderly,uneven and complex in structure.3.The PmABC gene family was analyzed by bioinformatics analysis.We identified 130 ABC genes from P.mume,which were divided into eight subfamilies.Among the ABC genes,55 were PmABCGs,including 29 half-size molecular transporters(WBC)and 26 full-size molecular transporters(PDR).And there are 24 WBC genes located on the cell membrane.Only the ABCG subfamily has the reverse domain "NBD-TMD" arrangement.The conserved motif of the same gene subfamily is similar,and most ABC genes contain introns.PmABCs were distributed unevenly on chromosomes,and some genes existed gene clusters and gene replication events,among which 9 pairs of genes were fragment replication and 14 pairs of genes were tandem duplication.The interspecific collinearity analysis showed that compared with the Prunus persica,the genetic relationship between P.mume and Prunus armeniaca was closer.4.The RNA-seq was used to analyze the samples of different tissues of flower organs.The differentially expressed genes(DEGs)were screened among the samples and analyzed by KEGG enrichment.The results showed that the sample has good correlation.Only the DEGs of filaments vs petals,anthers vs petals and filaments vs anthers could be enriched into the ABC transport pathway.In addition,most of the ABCG subfamily genes were specifically expressed in flowers.Importantly,they were also WBC genes and expressed high in filaments.We obtained the expression patterns of 17 WBC genes in different flower organs,and q RT-PCR was used to verify the expression in different parts of flower organs.PmABCG2,18,26 was significantly higher in anthers than in the other parts.The expression of PmABCG9 was high in different parts of flower organs,and the expression of PmABCG9 in filaments was higher than that in petals.The expressions of PmABCG13 and PmABCG23 were higher in filaments.5.The correlation analysis between the volatilization rate and ABCG genes expression level suggested that the volatilization difference of the key aromatic components in different parts of the P.mume were strongly correlated with the expression levels of the WBC genes in PmABCGs.The benzaldehyde and benzyl alcohol volatilization rate was both positively correlated with PmABCG2,18 and 26.In terms of gene expressions,the expression levels of PmABCG2,18 and 26 were relatively higher expressed in anthers.The volatilization rate of benzyl acetate had a significantly positive correlation with PmABCG9,13 and 23,while these genes were higher in filaments.We speculate that these highly expression genes may involve in the transmembrane transport of the key aromatic components of P.mume.