Effect of the Citrus Lycopene β-Cyclase Transgene on Carotenoid Metabolism in Transgenic Tomato Fruits

Lycopene β-cyclase (LYCB) is the key enzyme for the synthesis of β-carotene, a valuable component of the human diet. In this study, tomato constitutively express Lycb-1 was engineered. The β-carotene level of transformant increased 4.1 fold, and the total carotenoid content increased by 30% in the fruits. In the transgenic line, the downstream α-branch metabolic fluxes were repressed during the three developmental stages while α-carotene content increased in the ripe stage. Microarray analysis in the ripe stage revealed that the constitutive expression of Lycb-1 affected a number of pathways including the synthesis of fatty acids, flavonoids and phenylpropanoids, the degradation of limonene and pinene, starch and sucrose metabolism and photosynthesis. This study provided insight into the regulatory effect of Lycb-1 gene on plant carotenoid metabolism and fruit transcriptome.

番茄红素β-环化酶（Lycopene β-cyclase，LYCB）是β-胡萝卜素合成的关键酶，而β-胡萝卜素是人类膳食中极具价值的营养组分。本研究构建了组成型表达Lycb-1的转基因番茄植株。该转基因株系的果实中，β-胡萝卜素含量提升4.1倍，总类胡萝卜素含量提升30%。在该转基因株系的三个发育阶段中，下游α-分支代谢流均受到抑制，但在成熟阶段，α-胡萝卜素含量有所升高。成熟阶段的基因芯片（Microarray）分析结果显示，Lycb-1的组成型表达影响了多条代谢通路，包括脂肪酸、类黄酮与苯丙烷类物质的合成，柠檬烯和蒎烯的降解，淀粉与蔗糖代谢以及光合作用通路。本研究为解析Lycb-1基因对植物类胡萝卜素代谢及果实转录组的调控作用提供了重要见解。