Abstract
BackgroundColor directly affects fruit quality and consumer preference. In fig syconia, the female flower tissue is contained in a receptacle. Anthocyanin pigmentation of this tissue and the peel differs temporally and spatially. A transcriptome study was carried out to elucidate key genes and transcription factors regulating differences in fig coloring.ResultsAnthocyanins in the female flower tissue were identified mainly as pelargonidin-3-glucoside and cyanidin-3-rutinoside; in the peel, the major anthocyanins were cyanidin 3-O-glucoside and cyanidin-3-rutinoside. Anthocyanin content was significantly higher in the female flower tissue vs. peel before fig ripening, whereas at ripening, the anthocyanin content in the peel was 5.39 times higher than that in the female flower tissue. Light-deprivation treatment strongly inhibited peel, but not female flower tissue, anthocyanin pigmentation. RNA-Seq revealed 522 differentially expressed genes (recruited with criteria log2 ≥ 2 and P < 0.05) at fig ripening, with 50 upregulated and 472 downregulated genes in the female flower tissue. Light deprivation upregulated 1180 and downregulated 856 genes in the peel, and upregulated 909 and downregulated 817 genes in the female flower tissue. KEGG enrichment revealed significantly changed expression in the phenylpropanoid-biosynthesis and flavonoid-biosynthesis pathways in the peel, but not in the female flower tissue, with significant repression of FcCHS, FcCHI, FcF3H, FcF3’H, FcDFR and FcUFGT transcripts. Light deprivation led to differential expression of 71 and 80 transcription factor genes in the peel and female flower tissue, respectively. Yeast one-hybrid screen revealed that FcHY5 and FcMYB114 bind the promoter regions of FcCHS and FcDFR, respectively in the flavonoid-biosynthesis pathway.ConclusionsPhenylpropanoid- and flavonoid-biosynthesis pathways were differentially expressed spatially and temporally in the peel and female flower tissue of fig syconia; pathway expression in the peel was strongly regulated by light signal. Differentially expressed transcription factors were recruited as candidates to screen important expression regulators in the light-dependent and light-independent anthocyanin-synthesis pathway. Our study lays the groundwork for further elucidation of crucial players in fig pigmentation.
Highlights
Color directly affects fruit quality and consumer preference
VvMYBA1 and VvMYBA2 were revealed as key regulators in anthocyanin biosynthesis [8], whereas in pear, the key V-myb avian myeloblastosis viral oncogene homolog (MYB) was identified as PcMYB10 [9]
The female flower tissue pigmentation did not seem to be affected by light deprivation (Fig. 1a, Light deprivation), and no significant difference in anthocyanin content was detected compared to controls
Summary
The female flower tissue is contained in a receptacle. Anthocyanin pigmentation of this tissue and the peel differs temporally and spatially. A transcriptome study was carried out to elucidate key genes and transcription factors regulating differences in fig coloring. Members of three transcription factor families—MYB, bHLH and WD40—play pivotal roles in the regulation of anthocyanin- and other flavonoid-biosynthesis pathways by recruiting and forming different MYB–bHLH– WDR complexes [5]; MYBs play a leading role. VvMYBA1 and VvMYBA2 were revealed as key regulators in anthocyanin biosynthesis [8], whereas in pear, the key MYB was identified as PcMYB10 [9]
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