Plants grown under stress conditions generate excessive reactive oxygen species resulting in cell death. Therefore, plants activate the protection mechanism via antioxidant accumulation. Anthocyanins are flavonoid-derived secondary metabolites with high antioxidant properties. In this study, we analyzed and characterized the promoter region of RsMYB1, a positive regulator of anthocyanin biosynthesis. The RsMYB1 promoter was designed with four different fragment lengths (MP1, -1034; MP2, -830; MP3, -633; and MP4, -430 bp), and then each RsMYB1 promoter region was fused into a GUS gene for Arabidopsis transformation. The expression patterns of the RsMYB1 promoter constructs were analyzed at different developmental stages and under various abiotic stresses. The GUS expression pattern steadily increased with plant growth, and coincided with enzyme activity and a histochemical GUS assay. In response to drought, salt, sucrose, and low temperature, the GUS transcript level was highly expressed in MP4 in parallel with GUS enzyme activity. These assays indicated that the proximal region (-430 to -1 bp) of RsMYB1 was the core sequence that was induced by salt and low temperature. The expression level of RsMYB1 in the leaves of radish was highly activated and was consistent with the anthocyanin content under salt and low temperature conditions. These results suggest that induction of the RsMYB1 gene can activate the biosynthesis of anthocyanins, which are expected to help plants adapt to stress conditions due to their antioxidant activity.

Chlorophyll is an essential pigment involved in light absorption and electron transfer in photosynthesis, a photochemical process that is indispensable for plant growth and development. The biosynthesis of chlorophyll occurs in plastids and shares a common biosynthetic pathway with other tetrapyrroles. The chlorophyll metabolic pathway is divided into four distinct components: the common pathway, chlorophyll-specific biosynthetic pathway, chlorophyll cycle, and chlorophyll degradation pathway, which are regulated in developmental- and environmental-specific manners. During the early stages of plant growth, the expression of most chlorophyll biosynthetic genes is induced by light, resulting in an increase in chlorophyll accumulation, induction of high photosynthetic activity, and continuous plant growth. In contrast, during plant maturation, the expression of most of these genes is gradually downregulated, whereas genes involved in chlorophyll degradation are upregulated during leaf senescence. Chlorophyll biosynthesis is directly or indirectly regulated by the members of various transcription factor families. In this review, we describe representative mechanisms of transcription factor-mediated activation and repression of chlorophyll biosynthesis in response to light treatment. We also present an overview of recent studies that have examined all the enzymatic steps involved in chlorophyll metabolic pathways and their gene regulation at the transcriptional level, which will enable readers to gain a better understanding of chlorophyll metabolism.

In ornamental crops, the color and shape of flowers are one of the important traits. Generally, flower colors are determined by accumulating pigments such as carotenoids, flavonoids, and betalains. Among them, flavonoids are responsible for broad ranges of colors. Chrysanthemums are one of the most popular ornamental crops in the world, and there have been many efforts to change their flower color. In chrysanthemum flowers, cyanidin-based anthocyanin confers pink or red color, whereas terpenoid-based carotenoids are mainly responsible for yellow and green colors. However, blue colored chrysanthemums do not occur in nature. To date, there have been attempts to obtain blue or violet-colored chrysanthemum flowers through the introduction of a novel gene for accumulating delphinidin-based anthocyanins, while other studies have reported changing endogenous metabolites through the reconstruction of flavonoid biosynthesis. Since various transcription factors are involved in the regulation of flavonoid biosynthesis, it is important to understand not only the structural genes, but also the transcription factors required for the modification of flavonoid-based flower color. Therefore, in this paper, we describe the flavonoid biosynthetic pathway and its regulation, and review previous studies on the change in flower color through modification of flavonoid biosynthesis. This effort could be an important milestone in successfully achieving the modification of chrysanthemum flower color by means of plant biotechnology.

APETALA2/ethylene response factor (AP2/ERF) transcription factors are involved in biological and abiotic stress response, plant development, and growth. AP2/ERF genes are classified into five families (AP2, DREB, ERF, RAV, and soloist), and most genes belong to DREB and ERF families. So far, genomic analysis of DREB and ERF family genes of various plant species has been performed, and classifications based on the homology of AP2/ERF-specific DNA binding domain, arrangement of exons and introns, and similarity of group-specific conserved motifs have been conducted. These classifications provide plausible information for the prediction of AP2/ERF gene function. In this paper, an overview of the classification, structure, evolution, and function of AP2/ERF genes is described, and the functional properties and regulatory mechanisms of ERF family genes that have been identified are summarized by group according to the functional classification of Arabidopsis ERF family genes. This shows that group-specific conserved motifs of Arabidopsis ERF family genes are closely linked with group-specific functions and regulatory mechanisms, indicating that the effective functional prediction of ERF family genes through such a classification scheme can be usefully applied to the trait improvements of various plants.