Alternative splicing, activation of cryptic exons and amino acid substitutions in carotenoid biosynthetic genes are associated with lutein accumulation in wheat endosperm
Alternative splicing, activation of cryptic exons and amino acid substitutions in carotenoid biosynthetic genes are associated with lutein accumulation in wheat endosperm
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DOI：
10.1007/s10142-009-0121-3
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发表时间：
2009-08-01
影响因子：
2.9
通讯作者：
Pogson, Barry J.
中科院分区：
文献类型：
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作者：
Howitt, Crispin A.;Cavanagh, Colin R.;Pogson, Barry J.
小麦胚乳中类胡萝卜素的含量是面粉颜色的主要决定因素，这既影响了谷物的营养价值，也影响了其在不同应用中的用途。利用小麦-水稻的共性，确定了影响小麦胚乳中叶黄素含量的两个QTL的候选基因：epsilon-clecase(epsilon-LCY)和Psy-A1(Psy-A1)。对epsilon-LCY和PSY-A1序列变化的分析揭示了这两个QTL可能的原因机制。Epsilon-LCY中的点突变导致高叶黄素等位基因中保守的氨基酸被取代。这种替代在龙胆目中叶黄素积累量较高的物种中已观察到。在PSY-A1中，外显子2末端的序列复制创建了一个新的剪接位点，导致转录本的选择性剪接和一个隐蔽外显子的激活，从而产生四种不同的转录本：一个野生型转录本，两个具有早期终止的转录本，以及一个会产生内框内的转录本，尽管蛋白质更长。只有野生型剪接变异体产生一种具有酶活性的蛋白质，其mRNA丰度通过与其他剪接变异体的滴定而减少。这种野生型mRNA的减少被认为是导致PSY蛋白减少，从而导致小麦中类胡萝卜素含量的减少。
Endosperm carotenoid content in wheat is a primary determinant of flour colour and this affects both the nutritional value of the grain and its utility for different applications. Utilising wheat rice synteny two genes, epsilon-cyclase (epsilon-LCY) and phytoene synthase (Psy-A1), were identified as candidate genes for two of the QTL affecting lutein content in wheat endosperm. Analysis of the sequence changes in epsilon-LCY and Psy-A1 revealed possible causal mechanisms for both QTL. A point mutation in epsilon-LCY results in the substitution of a conserved amino acid in the high lutein allele. This substitution has been observed in high lutein-accumulating species from the Gentiales order. In Psy-A1, a sequence duplication at the end of exon 2 creates a new splice site and causes alternative splicing of the transcript and activation of a cryptic exon, resulting in four different transcripts: a wild-type transcript, two transcripts with early terminations and a transcript that would produce an in-frame, albeit longer protein. Only the wild-type splice variant produced an enzymatically active protein and its mRNA abundance was reduced by titration with the other splice variants. This reduction in wild-type mRNA is argued to result in a reduction in PSY protein and thus carotenoid content in wheat.