Abstract
To investigate the effect of light intensity on flavonoid biosynthesis, grapevine calluses were subjected to high light (HL, 250 μmol m−2 s−1) and dark (0 μmol m−2 s−1) in comparison to 125 μmol m−2 s−1 under controlled conditions (NL). The alteration of flavonoid profiles was determined and was integrated with RNA sequencing (RNA-seq)-based transcriptional changes of the flavonoid pathway genes. Results revealed that dark conditions inhibited flavonoid biosynthesis. Increasing light intensity affected flavonoids differently—the concentrations of flavonols and anthocyanins as well as the expressions of corresponding genes were less affected, whereas flavan-3-ol concentrations were predominantly increased, which caused enhanced trans-flavan-3-ol concentrations. Moreover, genes encoding leucoanthocyanidin reductase (LAR) exhibited different response patterns to light intensity changes—VviLAR1 expression increased with an increased light intensity, whereas VviLAR2 expression was insensitive. We further confirmed that the known transcription factors (TFs) involved in regulating flavan-3-ol biosynthesis utilized VviLAR1 as a target gene in grapevine calluses. In addition, VviLAR1 promoter activity was more sensitive to light intensity changes than that of VviLAR2 as determined using a transgenic Arabidopsis leaf system. These results suggested that light intensity had the most prominent effect on trans-flavan-3-ols in grapevine calluses and demonstrated that the two LAR genes had different response patterns to light intensity changes.
Highlights
Grape (Vitis vinifera L.) flavonoids have gained considerable attention as primary determinants of the quality and economic value of grapes and wines [1]
Two enzymes are specific for this branch, namely leucoanthocyanidin reductase (LAR) and anthocyanidin reductase (ANR), which are responsible for the formation of 2,3-trans-flavan-3-ols and 2,3-cis-flavan-3-ols, respectively [3]
In order to investigate why the two LAR genes showed different response patterns to light intensity changes, we examined the transcriptional level of transcription factors (TFs) by RNA sequencing (RNA-seq) and measured the promoter activity of two LAR genes though a transgenic Arabidopsis leaf system
Summary
Grape (Vitis vinifera L.) flavonoids have gained considerable attention as primary determinants of the quality and economic value of grapes and wines [1]. PAs, called condensed tannins, are important flavonoid compounds that give grapes and wines their astringency and bitterness [3]. They are oligomers and polymers of elementary flavan-3-ol units (such as (+)-catechin. Two enzymes are specific for this branch, namely leucoanthocyanidin reductase (LAR) and anthocyanidin reductase (ANR), which are responsible for the formation of 2,3-trans-flavan-3-ols (such as C) and 2,3-cis-flavan-3-ols (such as EC, ECG), respectively [3] In grapes, their function and expression patterns have been well characterized [6,7,8]
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