Abstract
BackgroundFlavonoid biosynthesis is strongly influenced by phytohormones. For example, methyl jasmonate (MeJA) enhances the flavonoid accumulation in pear. However, the molecular mechanism underlying the MeJA-induced flavonoid biosynthesis in pear is largely uncharacterized. Therefore, the transcriptome of pear calli treated with MeJA was analyzed to elucidate the mechanism regulating MeJA-mediated flavonoid biosynthesis.ResultsThe application of exogenous MeJA significantly enhanced flavonoid accumulation, especially anthocyanin, in pear calli. A weighted gene co-expression network analysis identified the differentially expressed genes associated with MeJA-induced flavonoid biosynthesis. The MeJA treatment upregulated the expression of the flavonoid biosynthesis pathway structural genes (PcCHS, PcCHI, PcF3H, PcDFR, PcANS, PcANR2a, and PcLAR1). The MYB family members were the main transcription factors regulating the MeJA-induced flavonoid biosynthesis, but the bHLH, AP2-EREBP, NAC, WRKY, and TIFY families were also involved. In addition to PcMYB10, which is a known positive regulator of anthocyanin biosynthesis in pear, several novel MYB candidates that may regulate flavonol and proanthocyanidin biosynthesis were revealed. Yeast two-hybrid and bimolecular fluorescence complementation assays demonstrated that PcMYB10 and PcMYC2 can directly interact with each other and bind to JAZ repressors (PcJAZ1 and PcJAZ2).ConclusionsThe PcMYB10–PcMYC2 molecular complex is likely involved in the regulation of jasmonate-mediated flavonoid biosynthesis at the transcript level. The data generated in this study may clarify the transcriptional regulatory network associated with the MeJA-induced flavonoid accumulation in pear calli and provide a solid foundation for future studies.
Highlights
Flavonoid biosynthesis is strongly influenced by phytohormones
methyl jasmonate (MeJA)-induced flavonoid accumulation in pear calli To assess the effect of MeJA on flavonoid biosynthesis, pear calli were transferred to Murashige and Skoog (MS) medium containing 50 μmol/L MeJA, whereas control calli were transferred to MS medium with 1% methanol
Overview of RNA sequencing Total RNA was extracted from pear calli sampled at 0, 12, and 48 h after the MeJA treatment and from the corresponding control samples for an RNA sequencing (RNA-seq) analysis
Summary
MeJA-induced flavonoid accumulation in pear calli To assess the effect of MeJA on flavonoid biosynthesis, pear calli were transferred to Murashige and Skoog (MS) medium containing 50 μmol/L MeJA, whereas control calli were transferred to MS medium with 1% methanol. 2583 and 1659 gene expression levels were upregulated and downregulated, respectively, in the MeJA-treated pear calli compared with the control levels at 48 h after the treatment (Additional file 1: Fig. S1). In addition to the MYB transcription factors, the bHLH genes, such as Pbr006544.1, Pbr017127.1, Pbr017379.1, and Pbr030521.1, exhibited significantly upregulated expression in the MeJA-treated calli relative to the control levels. The transcriptional profiles of the candidate MYB transcription factor genes indicated that most of these genes were more highly expressed in the MeJA-treated pear calli than in the control calli, with expression levels that were positively correlated with anthocyanin and flavonoid biosynthesis (Fig. 6b). The relative expression levels of selected MYB transcription factor genes determined by qRT-PCR were consistent with the FPKM values based on the sequencing data (Fig. 6c). These findings indicate that PcMYB10 and PcMYC2 can physically interact with each other and with PcJAZ1 and PcJAZ2
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