Abscisic acid and ethylene biosynthesis-related genes are associated with anthocyanin accumulation in purple ornamental cabbage (<i>Brassica oleracea</i> var. <i>acephala</i>)

Abstract

Purple ornamental cabbage (<i>Brassica oleracea</i> var. <i>acephala</i>) is a popular decorative plant, cultivated for its colorful leaf rosettes that persist in cool weather. It is characterized by green outer leaves and purple inner leaves, whose purple pigmentation is due to the accumulation of anthocyanin pigments. Phytohormones play important roles in anthocyanin biosynthesis in other species. Here, we identified 14 and 19 candidate genes putatively involved in abscisic acid (ABA) and ethylene (ET) biosynthesis, respectively, in <i>B. oleracea</i>. We determined the expression patterns of these candidate genes by reverse-transcription quantitative PCR (RT-qPCR). Among candidate ABA biosynthesis-related genes, the expressions of <i>BoNCED2.1</i>, <i>BoNCED2.2</i>, <i>BoNCED6</i>, <i>BoNCED9.1</i>, and <i>BoAAO3.2</i> were significantly higher in purple compared to green leaves. Likewise, most of the ET biosynthetic genes (<i>BoACS6</i>, <i>BoACS9.1</i>, <i>BoACS11</i>, <i>BoACO1.1</i>, <i>BoACO1.2</i>, <i>BoACO3.1</i>, <i>BoACO4</i>, and <i>BoACO5</i>) had significantly higher expression in purple compared to green leaves. Among these genes, <i>BoNCED2.1</i>, <i>BoNCED2.2</i>, <i>BoACS11</i>, and <i>BoACO4</i> showed particularly strong associations with total anthocyanin content of the purple inner leaves. Our results suggest that ABA and ET might promote the intense purple pigmentation of the inner leaves of purple ornamental cabbage.