Comparative Transcriptome Reveals Benzenoid Biosynthesis Regulation as Inducer of Floral Scent in the Woody Plant Prunus mume

Abstract

Mei (Prunus mume) is a peculiar woody ornamental plant famous for its inviting fragrance in winter. However, in this valuable plant, the mechanism behind floral volatile development remains poorly defined. Therefore, to explore the floral scent formation, a comparative transcriptome was conducted in order to identify the global transcripts specifying flower buds and blooming flowers of P. mume. Differentially expressed genes were identified between the two different stages showing great discrepancy in floral volatile production. Moreover, according to the expression specificity among the organs (stem, root, fruit, leaf), we summarized one gene cluster regulating the benzenoid floral scent. Significant gene changes were observed in accordance with the formation of benzenoid, thus pointing the pivotal roles of genes as well as cytochrome-P450s and short chain dehydrogenases in the benzenoid biosynthetic process. Further, transcription factors like EMISSION OF BENZENOID I and ODORANT I performed the same expression pattern suggesting key roles in the management of the downstream genes. Taken together, these data provide potential novel anchors for the benzenoid pathway, and the insight for the floral scent induction and regulation mechanism in woody plants.

Keywords: Mei; benzenoid biosynthesis; floral scent; transcription factors; transcriptome.

Figure 1

Different developing stages from P. mume (S1-S3) Developed bud; (S4) Squaring flower; (S5) fully blooming stage; (S6) fading stage. The flowers in stages of S2 and S4 were used to pool cDNA libraries for Illumina sequencing.

Figure 2

The DEGs of comparative transcriptome. The red block displayed 2,664 up-regulated and the green one established 5,149 down-regulated genes.

Figure 3

The enlarged cluster 46 (Blue block, p-value 6.5E-11) showed the scent related genes with a pattern of flower organ specificity. Clusters ordered based on number of genes and profiles ordered by significance.

Figure 4

Analysis of candidate genes using MapMan. Metabolism Overview revealed candidate genes assigned to 16 processes: cell wall metabolism, minor carbohydrate metabolism, starch metabolism, sugar metabolism, photosynthesis including light reactions, tetrapyrrole, Calvin Cycle, and photorespiration, glycolysis, metabolism, TCA Cycle, oxidative pentose phosphate pathway, mitochondrial electron transport, amino acid biosynthesis, nucleotide metabolism, lipid metabolism, and secondary metabolism. The blue diamonds mean up-regulated, otherwise in the red.

Figure 5

Display of secondary metabolism by Mapman. DEGs focus on the pathway of phenlypropanoids, Lignin and lignans, shikimate etc. The blue diamonds mean up-regulated, otherwise in the red.

Figure 6

Gene ontology categories of P.mume DEGs. The results are summarized in mainly three categories: biological process, cellular component and molecular function. The lines reveal the averages of genes in each category.

Figure 7

Proposed schematic representation of phenylpropanoid/ benzenoid biosynthetic pathway. Phenylpropanoid/ benzenoids are derived from phenylalanine, which itself is synthesized via the shikimate biosynthetic pathways. Larger arrows indicate there exist genes with strong expression level above 5 thousand of TPM. Each block means a fold change for a single gene.

Figure 8

Phylogenetic analysis of MYB transcription factors. TFs in red box mean high expression in blooming stage.

Figure 9

qRT-PCR results of 16 genes in the transcriptome. Yellow bars showed the relative expressions of S2 stage, blue ones showed expressions in the S4 stage.

Figure 10

Correlation analysis of fold change between q-PCR and RNA-seq.