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.

Identification of Fusarium oxysporum f. sp. raphani and investigation on fusarium wilt development by isolates and inoculation methods were conducted to establish a screening method for fusarium wilt-resistance in radish (Raphanus sativus L.) germplasm. Pathogenicity of F. oxysporum f. sp. raphani isolate, Heonggye-1 and Heonggye-2, to radish plants was confirmed by seedling test. Radish seedlings were inoculated by root-dipping and soil-drenching with or without root-wounding. For Heonggye-1 isolate, mean disease indexes were 4.13 and 3.91 by root-dipping and soil-drenching with root-wounding, respectively, but those were 1.87 and 1.88 without root-wounding. For Heonggye-2 isolate, mean disease indexes were 3.83 to 4.37 regardless of inoculation methods. Two-hundred sixty accessions of radish germplasm collected from 9 countries of Asia and Europe were evaluated for fusarium wilt-resistance by soil-drenching with root-wounding with Heonggye-2 isolate. Fifty-four resistant accessions with higher than 70% of the percentage of resistant seedlings in accession (P_R) and lower than 20% of the percentage of susceptible seedlings in accession (PS) was found. Eighteen susceptible accessions with lower than 20% of P_R and higher than 50% of PS were selected. These accessions could be used as breeding and research materials after re-evaluation of disease-resistance and characterization of agronomical traits.