State Key Laboratory of Crop Genetics and Germplasm Enhancement, Ministry of Agriculture and Rural Affairs Key Laboratory of Biology and Germplasm Enhancement of Horticultural Crops in East China, College of Horticulture, Nanjing Agricultural University, 1 Weigang, Nanjing, 210095, China.
Planta. 2022 Oct 29;256(6):104. doi: 10.1007/s00425-022-04016-9.
Distinct plastid types and ultrastructural changes are associated with differences in carotenoid pigment profiles in differently coloured carrots, and a variant of the OR gene, DcOR3 is vital for chromoplast biogenesis. Accumulation of different types and amounts of carotenoids in carrots impart different colours to their taproots. In this study, the carotenoid pigment profiles, morphology, and ultrastructure of plastids in 25 carrot varieties with orange, red, yellow, or white taproots were investigated by ultra-high performance liquid chromatography as well as light and transmission electron microscopy. α-/β-Carotene and lycopene were identified as colour-determining carotenoids in orange and red carrots, respectively. In contrast, lutein was identified as the colour-determining carotenoid in almost all tested yellow and white carrots. The latter contained only trace amounts of lutein as a unique detectable carotenoid. Striking differences in plastid types that coincided with distinct carotenoid profiles were observed among the differently coloured carrots. Microscopic analysis of the different carotenoid pigment-loaded plastids revealed abundant crystalloid chromoplasts in the orange and red carrots, whereas amyloplasts were dominant in most of the yellow and white carrots, except for the yellow carrot 'Yellow Stone', where yellow chromoplasts were observed. Plastoglobuli and crystal remnants, the carotenoid sequestering substructures, were identified in crystalloid chromoplasts. Crystal remnants were often associated with a characteristic undulated internal membrane in orange carrots or several undulated membranes in red carrots. No crystal remnants, but some plastoglobuli, were observed in the plastids of all tested yellow and white carrots. In addition, the presence of chromoplast in carrot taproots was found to be associated with DcOR3, a natural variant of DcOR3, which was previously reported to be co-segregated with carotene content in carrots. Knocking out DcOR3 in the orange carrot 'Kurodagosun' depressed chromoplast biogenesis and led to the generation of yellow carrots. Our results support that DcOR3 is vital but insufficient for chromoplasts biogenesis in carrots, and add to the understanding of the formation of chromoplasts in carrots.
不同类型的质体和超微结构的变化与不同颜色胡萝卜中类胡萝卜素色素谱的差异有关，而 DcOR3 基因的变体对于质体生物发生至关重要。胡萝卜中不同类型和数量的类胡萝卜素的积累赋予了其主根不同的颜色。在这项研究中，通过超高效液相色谱以及光和透射电子显微镜研究了 25 个具有橙色、红色、黄色或白色主根的胡萝卜品种的质体色素谱、形态和超微结构。α-/β-胡萝卜素和番茄红素分别被鉴定为橙色和红色胡萝卜的颜色决定类胡萝卜素。相比之下，叶黄素被鉴定为几乎所有测试的黄色和白色胡萝卜的颜色决定类胡萝卜素。后者仅含有痕量的叶黄素作为唯一可检测到的类胡萝卜素。在不同颜色的胡萝卜中观察到明显不同的质体类型，与独特的类胡萝卜素谱一致。对不同类胡萝卜素负荷质体的微观分析表明，橙色和红色胡萝卜中存在丰富的结晶质体，而在大多数黄色和白色胡萝卜中，淀粉体占主导地位，除了黄色胡萝卜“Yellow Stone”外，其中观察到黄色质体。质体小球体和晶体残余物，即类胡萝卜素隔离的亚结构，在结晶质体中被鉴定出来。晶体残余物通常与橙色胡萝卜中特征性的波浪形内膜或红色胡萝卜中的几个波浪形内膜相关联。在所有测试的黄色和白色胡萝卜的质体中都没有观察到晶体残余物，但观察到一些质体小球体。此外，在胡萝卜主根中存在质体与 DcOR3 有关，DcOR3 是 DcOR3 的天然变体，先前的研究表明它与胡萝卜中的类胡萝卜素含量共分离。在橙色胡萝卜“Kurodagosun”中敲除 DcOR3 会抑制质体生物发生，并导致产生黄色胡萝卜。我们的结果支持 DcOR3 对于胡萝卜质体生物发生至关重要但不充分，并且增加了对胡萝卜质体形成的理解。
