Abstract
Keeping green leaf color at the time of harvest is one of the important traits for breeding of Brassica oleracea var. capitata f. alba, and this trait is related to low anthocyanin contents. To understand the differential accumulation of anthocyanins in cabbage, we selected high anthocyanin accumulators (HAAs) and low anthocyanin accumulator (LAAs) of cabbages and examined the anthocyanin content and the expression of anthocyanin biosynthesis-related genes. Among many genes investigated, BoDFR1 was found to be closely related to anthocyanin accumulation, even under low temperature (LT) conditions. BoDFR1 sequence analyses between HAAs and LAAs revealed that there is a single nucleotide polymorphism (SNP) (1118T/A) in the coding sequence, which substitutes one amino acid from Leu261 to His261; we named BoDFR1 with His261 substitution as BoDFR1v. This amino acid substitution did not affect dihydroflavonol 4-reductase (DFR) activity and substrate specificity, but the polymorphism showed tight association to the BoDFR1 expression, i.e., high level expression of BoDFR1 and low level expression of BoDFR1v under LT conditions. The high levels of BoDFR1 expression were due to the high levels of BoMYB114 and BobHLH expressions combined with low level expression of BoMYBL2, a repressor MYB. On the other hand, low levels of BoDFR1v expression seemed to be related to very low level expressions of BoMYB114 and BobHLH combined with a high level expression of BoMYBL2. It seems that different expression levels of these regulatory genes for MBW (MYB-bHLH-WD40) complex between HAAs and LAAs regulate BoDFR expression and anthocyanin accumulation. Using a single nucleotide polymorphism (SNP) between BoDFR1 and BoDFR1v, molecular markers for PCR and high resolution melt analyses were developed and validated to distinguish between HAAs and LAAs. Combined use of the BoDFR1 SNP marker with other stress markers, such as a cold tolerant marker, will greatly improve cabbage breeding.
Highlights
Anthocyanins are water-soluble plant pigments that range from blue to red in color
Genes encoding structural proteins are divided into two groups: early biosynthetic genes (EBGs), which are involved in the initial stages of anthocyanin biosynthesis such as chalcone synthase (CHS), chalcone isomerase (CHI), and flavanone 3-hydroxylase (F3H) [27], and late biosynthetic genes (LBGs), which are involved in the late stages of anthocyanin biosynthesis such as dihydroflavonol
To identify the gene that regulates anthocyanin accumulation under low temperature (LT) conditions, we examined the expression profiles of two early anthocyanin biosynthetic genes (BoCHS and BoF3H) and two late anthocyanin biosynthetic genes (BoDFR1 and BoLDOX) encoding structural proteins in the LT tolerant inbred line BN106
Summary
Anthocyanins are water-soluble plant pigments that range from blue to red in color. Anthocyanins impart color to leaves, flowers, and fruits, attracting pollinators and seed distributors [1,2,3,4], Agronomy 2020, 10, 602; doi:10.3390/agronomy10040602 www.mdpi.com/journal/agronomyAgronomy 2020, 10, 602 and protect plants from abiotic stresses, such as ultraviolet (UV) radiation, cold, and drought, and biotic stresses such as microbial infection [5,6,7,8,9,10,11,12,13]. Anthocyanins are water-soluble plant pigments that range from blue to red in color. Anthocyanin biosynthesis is controlled by several genes encoding structural proteins and transcription factors. Genes encoding structural proteins are divided into two groups: early biosynthetic genes (EBGs), which are involved in the initial stages of anthocyanin biosynthesis such as chalcone synthase (CHS), chalcone isomerase (CHI), and flavanone 3-hydroxylase (F3H) [27], and late biosynthetic genes (LBGs), which are involved in the late stages of anthocyanin biosynthesis such as dihydroflavonol. The expression of LBGs is tightly regulated by MYB, basic helix-loop-helix (bHLH), and WD-repeat proteins [31,32], which together form the MBW complex and regulate the spatiotemporal expression pattern of LBGs in response to developmental and environmental factors [30,32,33]
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