Analysis of carotenoid accumulation and expression of carotenoid biosynthesis genes in different organs of Chinese cabbage (Brassica rapa subsp. pekinensis)

Abstract

The relationship between carotenoid accumulation and expression of carotenoid biosynthesis genes was investigated in the flowers, stems, young leaves, old leaves, and roots of Chinese cabbage (Brassica rapa subsp. pekinensis). Quantitative real-time PCR analysis showed that the mRNA levels of BrPSY, BrPDS, BrZDS, BrLCYB, BrLCYE, BrCHXB, and BrZEP leading to the production of carotenoids were highest in the flowers or the leaves and lowest in the roots of Chinese cabbage. In contrast, the mRNA expression of BrNCED, a gene involved in abscisic acid (ABA) biosynthesis, was highest in the roots. High-performance liquid chromatography revealed that carotenoids, namely, lutein and β-carotene, were distributed predominantly in the flowers and leaves, with very little in the underground organ, the roots. Specifically, old leaves contained 120.3 μg/g lutein and 103.93 μg/g β-carotene, which is the most potent dietary precursor of vitamin A. Moreover, we found a relatively large amount of cis isomers of β-carotene, namely, 9-cis β-carotene and 13-cis β-carotene, in Chinese cabbage. These results provide insight into carotenoid biosynthetic mechanisms in Chinese cabbage and may be helpful in the metabolic engineering of carotenoid biosynthesis in plants.

Keywords: Brassica rapa subsp. pekinensis; Chinese cabbage; beta-carotene; carotenoid biosynthesis genes; carotenoids.

Table 1. Primers used for real-time PCR

Table 2. Carotenoid composition and content in different organs of Chinese cabbage (μg·g^-1 dry weight). Results are expressed as the mean (± standard error) (n = 3).

Figure 1. Carotenoid biosynthesis pathway in plants. GGDP, geranylgeranyl diphosphate; PSY, phytoene synthase; PDS, phytoene desaturase; ZDS, ξ-carotene de saturase; LCYB, lycopene β-cyclase; LCYE, lycopene ε-cyclase; CHXB, β-ring carotene hydroxylase; CHXE, ε-ring carotene hydroxylase; ZEP, zeaxanthin epoxidase; NCED, 9-cis epoxycarotenoid dioxygenase

Figure 2. Expression of carotenoid biosynthesis genes in different organs of Chinese cabbage. The values and error bars represent the average and standard error from three independent reactions.