Kang Baoshan, Gu Qinsheng, Tian Peng, Xiao Liangjun, Cao Haipeng, Yang Wencai
Beijing Key Laboratory of Growth and Developmental Regulation for Protected Vegetable Crops, Department of Vegetable Science, China Agricultural University, No. 2 Yuanmingyuan Xilu, Beijing, 100193, China.
Planta. 2014 Nov;240(5):1011-21. doi: 10.1007/s00425-014-2052-z. Epub 2014 Mar 25.
Carotenoid content is the primary determinant of fruit color that affects nutritional value and appearance in tomato. Phytoene synthase (PSY) is the key regulatory enzyme in the carotenoid biosynthesis pathway. Absent function of PSY1 in tomato fruit results in yellow flesh phenotype. We, here, report that two different transcripts, a wild-type (Psy1) and a chimeric mRNA (Psy1/Unknown), exist in a yellow-fruited tomato accession PI 114490. Psy1/Unknown is generated by joining exons from two different genes, Psy1 and an unknown gene, transcribed using both complementary DNA strands. The Psy1 shows low expression in the fruit of PI 114490, while the expression of Psy1/Unknown in the fruit of PI 114490 shows the same pattern as Psy1 in red fruit. The PSY1/Unknown has a lower function than PSY1 in a bacterial expression system. Coincidence of one single-nucleotide polymorphism (SNP) in the fourth intron and one simple sequence repeat (SSR) with 19 AT repeats in the downstream sequence of Psy1 gene with Psy1/Unknown in a set of yellow-fruited tomato lines indicates that Psy1/Unknown might be caused by the SNP and/or SSR. One possible explanation of these observations is trans-splicing. Severely reduced Psy1 transcript caused by Psy1/Unknown results in low accumulation of carotenoid and yellow flesh in PI 114490.
类胡萝卜素含量是影响番茄营养价值和外观的果实颜色的主要决定因素。八氢番茄红素合酶（PSY）是类胡萝卜素生物合成途径中的关键调控酶。番茄果实中PSY1功能缺失会导致果肉呈黄色表型。我们在此报告，在一个黄果番茄种质PI 114490中存在两种不同的转录本，一种是野生型（Psy1），另一种是嵌合mRNA（Psy1/未知）。Psy1/未知是通过连接来自两个不同基因Psy1和一个未知基因的外显子产生的，这两个基因使用两条互补DNA链进行转录。Psy1在PI 114490的果实中表达较低，而Psy1/未知在PI 114490果实中的表达模式与红色果实中Psy1的表达模式相同。在细菌表达系统中，PSY1/未知的功能比PSY1低。在一组黄果番茄品系中，Psy1基因第四内含子中的一个单核苷酸多态性（SNP）和下游序列中一个具有19个AT重复的简单序列重复（SSR）与Psy1/未知同时出现，这表明Psy1/未知可能是由SNP和/或SSR引起的。对这些观察结果的一种可能解释是反式剪接。由Psy1/未知导致的Psy1转录本严重减少，导致PI 114490中类胡萝卜素积累量低和果肉呈黄色。
