Abstract
The red coloration of litchi fruit depends on the accumulation of anthocyanins. The anthocyanins level in litchi fruit varies widely among cultivars, developmental stages and environmental stimuli. Previous studies on various plant species demonstrate that anthocyanin biosynthesis is controlled at the transcriptional level. Here, we describe a litchi R2R3-MYB transcription factor gene, LcMYB1, which demonstrates a similar sequence as other known anthocyanin regulators. The transcription levels of the LcMYB1 and anthocyanin biosynthetic genes were investigated in samples with different anthocyanin levels. The expression of LcMYB1 was strongly associated with tissue anthocyanin content. LcMYB1 transcripts were only detected in anthocyanin-accumulating tissues and were positively correlated with anthocyanin accumulation in the pericarps of 12 genotypes. ABA and sunlight exposure promoted, whereas CPPU and bagging inhibited the expression of LcMYB1 and anthocyanin accumulation in the pericarp. Cis-elements associated with light responsiveness and abscisic acid responsiveness were identified in the promoter region of LcMYB1. Among the 6 structural genes tested, only LcUFGT was highly correlated with LcMYB1. These results suggest that LcMYB1 controls anthocyanin biosynthesis in litchi and LcUFGT might be the structural gene that is targeted and regulated by LcMYB1. Furthermore, the overexpression of LcMYB1 induced anthocyanin accumulation in all tissues in tobacco, confirming the function of LcMYB1 in the regulation of anthocyanin biosynthesis. The upregulation of NtAn1b in response to LcMYB1 overexpression seems to be essential for anthocyanin accumulation in the leaf and pedicel. In the reproductive tissues of transgenic tobacco, however, increased anthocyanin accumulation is independent of tobacco's endogenous MYB and bHLH transcriptional factors, but associated with the upregulation of specific structural genes.
Highlights
The colors of flowers and fruits mainly result from the accumulation of anthocyanins, a group of secondary metabolites that are synthesized via the flavonoid pathway [1]
The structural genes involved in the anthocyanin biosynthetic pathway of plants include chalcone synthase (CHS), chalcone isomerase (CHI), flavanone 3-hydroxylase (F3H), flavonoid 39-hydroxylase (F39H), dihydroflavonol 4-reductase (DFR), anthocyanidin synthase (ANS), and UDP-glucose: flavonoid 3-O-glucosyltransferase (UFGT)
Numerous studies demonstrate that anthocyanin accumulation is largely regulated at the transcriptional factors which manipulate the expression of structural genes in the anthocyanin biosynthetic pathway [8]
Summary
The colors of flowers and fruits mainly result from the accumulation of anthocyanins, a group of secondary metabolites that are synthesized via the flavonoid pathway [1]. The structural genes involved in the anthocyanin biosynthetic pathway of plants include chalcone synthase (CHS), chalcone isomerase (CHI), flavanone 3-hydroxylase (F3H), flavonoid 39-hydroxylase (F39H), dihydroflavonol 4-reductase (DFR), anthocyanidin synthase (ANS), and UDP-glucose: flavonoid 3-O-glucosyltransferase (UFGT). These genes are well characterized in model plants [2,3] and fruits including grape [4], apple [5], Chinese bayberry [6], and litchi [7]. FaMYB1 represses transcription of anthocyanin-related genes during maturation, and the biosynthesis of proanthocyanidins is inhibited in the leaves of FaMYB1 transgenic Lotus corniculatus [24,25] These results suggest functional differences between various R2R3-MYB proteins
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