National Watermelon and Melon Improvement Center, Beijing Academy of Agricultural and Forestry Sciences, Key Laboratory of Biology and Genetic Improvement of Horticultural Crops (North China), Beijing Key Laboratory of Vegetable Germplasm Improvement, Beijing 100097, China.
National Watermelon and Melon Improvement Center, Beijing Academy of Agricultural and Forestry Sciences, Key Laboratory of Biology and Genetic Improvement of Horticultural Crops (North China), Beijing Key Laboratory of Vegetable Germplasm Improvement, Beijing 100097, China
Plant Physiol. 2020 Jul;183(3):1171-1183. doi: 10.1104/pp.19.01409. Epub 2020 Apr 22.
Red-fleshed watermelons () that accumulate lycopene in their flesh cells have been selected and domesticated from their pale-fleshed ancestors. However, the molecular basis of this trait remains poorly understood. Using map-based cloning and transgenic analysis, we identified a lycopene β-cyclase () gene that controls the flesh color of watermelon. Down-regulation of caused the flesh color to change from pale yellow to red, and overexpression in the red-fleshed line caused the flesh color to change to orange. Analysis of single-nucleotide polymorphisms using 211 watermelon accessions with different flesh colors revealed that two missense mutations between three haplotypes ( , , and ) were selected and largely fixed in domesticated watermelon. Proteins derived from these three haplotypes were localized in plastids to catalyze the conversion of lycopene to β-carotene and showed similar catalytic abilities. We revealed that ClLCYB protein abundance, instead of transcript level, was negatively correlated with lycopene accumulation. Different amounts of ClLCYB protein degradation among the haplotypes were found in ClLCYB transgenic Arabidopsis () lines. After treatment with the proteasome inhibitor MG132, the concentration of ClLCYB increased noticeably compared with other ClLCYB proteins. These results indicate that natural missense mutations within influence ClLCYB protein abundance and have contributed to the development of red flesh color in domesticated watermelon.
从果肉细胞中积累番茄红素的红肉西瓜被选育和驯化而来。然而，这一特征的分子基础仍知之甚少。通过基于图谱的克隆和转基因分析，我们鉴定了一个控制西瓜果肉颜色的番茄红素 β-环化酶（）基因。下调导致果肉颜色从浅黄色变为红色，而在红肉系中过表达则导致果肉颜色变为橙色。对 211 个具有不同果肉颜色的西瓜品种进行单核苷酸多态性分析表明，三个单倍型（、和）之间的两个错义突变被选择并在驯化西瓜中大量固定。这三个单倍型衍生的蛋白定位于质体中，催化番茄红素转化为 β-胡萝卜素，表现出相似的催化能力。我们揭示了 ClLCYB 蛋白丰度而非转录水平与番茄红素积累呈负相关。在 ClLCYB 转基因拟南芥（）系中发现三个单倍型的 ClLCYB 蛋白降解量不同。用蛋白酶体抑制剂 MG132 处理后，ClLCYB 的浓度与其他 ClLCYB 蛋白相比明显增加。这些结果表明，ClLCYB 内的天然错义突变影响 ClLCYB 蛋白丰度，并导致驯化西瓜红色果肉的形成。
