Ultraviolet and environmental stresses involved in the

African Journal of Biotechnology Vol. 7 (25), pp. 4966-4972, 29 December, 2008

Available online at 2bad3836852458fb770b56f4/AJB

ISSN 1684–5315 ? 2008 Academic Journals

Review

Ultraviolet and environmental stresses involved in the induction and regulation of anthocyanin biosynthesis:

A review

Jia Guo, Woong Han and Myeong-Hyeon Wang*

School of Biotechnology, Kangwon National University, Chuncheon, 200-701, South Korea

Accepted 12 December, 2008

Anthocyanins are the most conspicuous class of flavonoids which present a large class of secondary plant metabolites. Anthocyanins are important to many diverse functions within plants. Anthocyanin biosynthetic pathway is well established. Two classes of genes required for anthocyanin biosynthesis have been extensively characterized; the structural genes encoding the enzymes that directly participate in the formation of anthocyanins and other flavonoids, and the regulatory genes that control the transcription of structural genes. Light is one of the most important environmental factors regulating plant development and genes expression. Ultraviolet takes up 7% of sunlight and it stimulates distinct responses in plant. Both UV-A and low influence of UV-B can induce the accumulation of anthocyanin via induction of the expression of anthocyanin biosynthesis genes.

Besides, the modulation of anthocyanin by environmental and developmental factors has been observed. A number of genes involved in anthocyanin biosynthesis are induced by abiotic stresses.

Key words: Anthocyanins, ultraviolet, photoreceptor, environmental stress.

INTRODUCTION

Flavonoids are a class of secondary metabolites widespread in various plants (Tahara, 2007). Flavonoids perform major roles in plants such as UV protection, defense against pathogens and pests, pollen fertility, signaling with microorganisms, auxin transport regulation, and pigmentation (Winkel-Shirley, 2001). Today more than 10,000 varieties of flavonoids have been identified (Tahara, 2007; Dixon and Paiva, 1995). Anthocyanins are the largest group of water-soluble pigments in the plant kingdom (Kong et al., 2003).

Flavonoids consist of anthocyanins, flavonoids, cate-chins, phenolic acids, secoiridoids, stilbenes, coumarins and isoflavones which are well known in vegetable crops (Corbett, 1974). Figure 1 shows that synthesis of flavor-noids used the phenylpropanoid metabolic pathway in which the amino acid phenylalanine is used to produce 4-coumaroyl-CoA (Shih et al., 2008). Anthocyanins are commonly found in the red, blue, and purple colors of

*Corresponding author. E-mail: mhwang@kangwon.ac.kr. Tel: 82-33-250-6486. Fax: 82-33-241-6480. fruits, vegetables, flowers, and other plant tissues or products and their amounts are especially high in berries and red wines (Mateus et al., 2001).Anthocyanins color shows variable differences- the aglycone, the pattern of glycosylation, and the amount of esterification of the sugars with aromatic acids or aliphatic, and the presence of co-pigments (Mazza et al., 2004). Approximately 500 individual anthocyanins have been identified (Ghosh, 2007).

In the plants, anthocyanidins can be classified to six categories according to the number and position of hydroxyl and methoxyl groups on the flavan nucleus, including pelargonidin, cyanidin, delphinidin, peonidin, petunidin, and malvidin (Figure 2; Tahara, 2007). The main structures of anthocyanin consist of three main parts and three R groups (Mazza, 2007). The anthocyani-dins compounds show various functions in counteracting the negative effects of nitrogen and oxygen reactive species, maintaining the redox homeostasis of biological fluids, and preventing human disease such as athero-sclerosis, ardiovascular, and other degenerative pathologies such as diabetes, cancer, Parkinson’s and Alzheimer’s diseases (González-Gallego et al., 2007;

Guo et al. 4967

Figure 1. Pathways of favonoid biosynthesis. The initial step is catalyzed by chalcone synthase (CHS)

using malonyl CoA and p-coumaroyl CoA as substrates. Enzymes are abbreviated as follows:

anthocyanidin synthase (ANS), anthocyanidin reductase (ANR), chalcone isomerase (CHI), dihydroxavonol 4-reductase (DFR), xavanone 3-hydroxylase (F3H), xavone synthases I or II (FNS I or

FNS II), xavonoid 3-hydroxylase (F3H), xavonoid 3-O-glycosyltransferase (FGT), xavonol synthase

(FLS), and leucoanthocyanidin reductase (LAR).

Harborne and Williams, 2000). In nature, the most commonly occurring anthocyanidin is cyanidin (Tahara, 2007). Researchers have used numerous strategies to determine the amounts of individual species and to estimate the antioxidative power of phenolic compounds in plants (Holton and Cornish, 1995). This review explains the anthocyanin and genes related to anthocya-nin biosynthesis involved in ultraviolet irradiation and various environmental factors.

CHARACTERIZATION OF GENES INVOLVED IN ANTHOCYANIN BIOSYNTHESIS

Anthocyanin biosynthesis has been extensively studied in several plant species, and, therefore, detailed information of the course of reactions is available (Mol et al., 1989; Forkmann, 1991). Two classes of genes are required for anthocyanin biosynthesis, the structural genes encoding the enzymes that directly participate in the formation of anthocyanins and other flavonoids, and the regulatory genes that control the transcription of structural genes. The study of the genetic of anthocyanin synthesis began last century with Mendel’s work on flower colour in peas (Fairbanks and Schaalje, 2007).

Genetic loci were usually correlated with easily observed color changes in the early studies (Dooner et al., 1991; Gerats et al., 1982; Sparvoli et al., 1994). In the recent 70 years, genetics and biochemistry on anthocyanin metabolism were deeply studied. After the structures of anthocyanin and other flavonoids were determined, it was possible to correlate single genes with corresponding anthocyanins. Maize (Zea mays), snap-dragon (Antirrhinum majus) and petunia (Petunia hyvrida) are three important species for studying the anthocyanin biosynthetic pathway and isolating genes controlling the biosynthesis of flavonoids (Wiering and de Vlaming, 1973).

Two classes of genes are required for anthocyanin biosynthesis, the structural genes encoding the enzymes that directly participate in the formation of anthocyanins and other flavonoids, and the regulatory genes that control the transcription of structural genes. Over the last few years, many structural genes that encode enzymes related to anthocyanin biosynthesis and the transcription factors that activate or repress the structural genes have been cloned. These have contributed to an understanding of the molecular level of anthocyanin bio-

4968 Afr. J. Biotechnol.

Figure 2. Structural classification of general anthocyanidin species (Tahara, 2007).

synthesis in higher plants.

Structural genes

A number of structural genes have been isolated from maize, snapdragon, and petunia through proteins purification, transposon tagging, PCR and differential screening. The first flavonoid biosynthetic gene isolated was CHS gene from parsley through a combination method of differential screening and hybrid-selected translation (Kreuzaler et al., 1983). Two years later, the parsley CHS clone was used as a molecular probe to isolate clones of two different CHS genes from petunia (Reif et al., 1985). A CHI cDNA was first isolated from French bean using antibodies made against the purified enzymes in 1988 (van Tunen et al., 1988).

A combination of differential screening and genetic mapping was used to isolate a cDNA clone corres-ponding to F3H (Martin et al., 1991). A cDNA encoding F3H was isolated from petals of petunia (Britsch et al., 1992). Using the petunia F3H cDNA clone as a heterologous probe, the corresponding cDNAs were cloned from carnation, China aster, and stock (British et al., 1993). F3’5’H cDNA was isolated from petunia via PCR amplification (Holton et al., 1993). DFR genes have been isolated from maize and snapdragon by transposon tagging and ANS gene was first isolated in maize by transposon tagging, and then it was isolated from snapdragon and petunia (O’Reilly et al., 1985). A snapdragon DFR clone was used to isolate a homo-logous gene from petunia (Beld et al., 1989). The maize Bzl gene, encoding UDP g1ucose:flavonoid 3-Oglucosyltransferase (3GT), was isolated by transposon tagging with Ac (Dooner et al., 1985). A putative 3GT clone, pJAM338, was isolated from snapdragon using the maize gene as a probe (Martin et al., 1991). AMT clone was cloned in 1993 (Quattocchio et al., 1993).

Regulatory genes

Regulatory genes influence the intensity and pattern of anthocyanin biosynthesis and generally control expression of many different structural genes. Isolation of these genes mainly made use of transposon tagging technology (Nevers and Saedler, 1977; Nevers et al., 1986). The R gene family determines the timing, distribution, and amount of anthocyanin pigmentation in maize. Afterwards, other regulatory genes B, C1, PI and Vpl genes were isolated successively (Chandler et al., 1989; Cone et al., 1993; Dellaporta et al., 1988; McCarty et al., 1989). Goodrich isolated Del gene from snapdragon in 1992 (Goodrich et al., 1992). Quattrocchio isolated An2 and An4 genes from petunia (Quattrocchio et al., 1993). An2 controls the transcription of these anthocyanin genes in the flower limb and An4 controls expression of the same set of genes in the anthers. Interestingly, gene R, Sn, Lc showed similar sequences to B; C1 and Pl were also shown to be homologous; the Del and R family gene in maize share high sequence similarity; and An2 sequence was similar to C1 and Pl. These observations suggest the synthesis of anthocyanin in different species was regulated by similar regulatory factors.

EFFECT OF ULTRAVIOLET ON ANTHOCYANIN

Light is one of the most important environmental factors regulating plant development and the expression of plant genes. A plant’s ability to maximize its photosynthetic productivity depends on its capacity to sense, evaluate, and respond to light quality, quantity, and direction. The sun light comprises seven percent of UV range (200-400 nm). Most UV-A and a larger proportion of the UV-B spectrum reaches the Earth’s surface with serious implications for all living organisms (Xiong and Day, 2001).