Abstract
BackgroundOrnamental cabbage (Brassica oleracea var. acephala) is an attractive landscape plant that remains colorful at low temperatures during winter. Its key feature is its inner leaf coloration, which can include red, pink, lavender, blue, violet and white. Some ornamental cabbages exhibit variation in leaf color pattern linked to leaf developmental stage. However, little is known about the molecular mechanism underlying changes in leaf pigmentation pattern between developmental stages.ResultsThe transcriptomes of six ornamental cabbage leaf samples were obtained using Illumina sequencing technology. A total of 339.75 million high-quality clean reads were assembled into 46,744 transcripts and 46,744 unigenes. Furthermore, 12,771 genes differentially expressed across the different lines and stages were identified by pairwise comparison. We identified 74 and 13 unigenes as differentially expressed genes related to the anthocyanin biosynthetic pathway and chlorophyll metabolism, respectively. Among them, three unigenes (BoC4H2, BoUGT9, and BoGST21) and six unigenes (BoHEMA1, BoCRD1, BoPORC1, BoPORC2, BoCAO, and BoCLH1) were found as candidates for the genes encoding enzymes in the anthocyanin biosynthetic pathway and chlorophyll metabolism, respectively. In addition, two unigenes (BoRAX3 and BoTRB1) as MYB candidates, two unigenes (BoMUTE1, and BHLH168-like) as bHLH candidates were identified for purple pigmentation in ornamental cabbage.ConclusionOur results indicate that the purple inner leaves of purple ornamental cabbage result from a high level of anthocyanin biosynthesis, a high level of chlorophyll degradation and an extremely low level of chlorophyll biosynthesis, whereas the bicolor (purple/green) outer leaves are due to a moderate level of anthocyanin biosynthesis, a high level of chlorophyll degradation and a very low level of chlorophyll biosynthesis. In white ornamental cabbage, the white inner leaves are due to an extremely low level or absence of anthocyanin biosynthesis, a high level of chlorophyll degradation and a very low level of chlorophyll biosynthesis, whereas the bicolor (white/green) leaves are due to a high level of chlorophyll degradation and a low level of chlorophyll biosynthesis and absence of anthocyanin biosynthesis. These results provide insight into the molecular mechanisms underlying inner and bicolor leaf pigmentation in ornamental cabbage and offer a platform for assessing related ornamental species.
Highlights
Ornamental cabbage (Brassica oleracea var. acephala) is an attractive landscape plant that remains colorful at low temperatures during winter
We carried out transcriptome analysis by RNA-seq to understand the molecular mechanism underlying the development of the purple inner leaf and the bicolor leaf with purple center and green margin in purple ornamental cabbage, as well as the white inner leaf and bicolor leaf with white center and green margin in white ornamental cabbage
Our results suggest that the purple inner leaves of purple ornamental cabbage are due to the combination of high level of anthocyanin biosynthesis, high level of chlorophyll degradation and extremely low chlorophyll biosynthesis at that developmental stage compared to other stages
Summary
Ornamental cabbage (Brassica oleracea var. acephala) is an attractive landscape plant that remains colorful at low temperatures during winter. Acephala) is an attractive landscape plant valued for its fascinating inner leaf coloration and its ability to grow and remain colorful at temperature as low as 15–20 °F [1, 2] It is becoming increasingly well-known for its long-lasting, colorful leaves and hardiness during fall and early winter when many plants senesce. The characteristic feature of ornamental cabbage is the inner leaf colors, which can include red, pink, lavender, blue, violet and white [2]. Some ornamental cabbages exhibit variation in color pattern in the leaves along with leaf developmental stages This spatiotemporal variation in leaf pigmentation is due to the accumulation of anthocyanins [2, 3]. Leaves accumulate increasing amounts of chlorophyll and wax compounds that provide photoprotection, and alter their color from red to green through degradation of anthocyanins (reviewed by Oren-Shamir [4])
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