title: Alternative splicing, activation of cryptic exons and amino acid substitutions in carotenoid biosynthetic genes are associated with lutein accumulation in wheat endosperm.
abstract: 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.
authors.affiliation: CSIRO Food Futures National Research Flagship, Canberra, Australia. Crispin.Howitt@csiro.au
authors.forename: Crispin A
authors.initials: CA
authors.lastname: Howitt
authors.forename: Colin R
authors.initials: CR
authors.lastname: Cavanagh
authors.forename: Andrew F
authors.initials: AF
authors.lastname: Bowerman
authors.forename: Christopher
authors.initials: C
authors.lastname: Cazzonelli
authors.forename: Lynette
authors.initials: L
authors.lastname: Rampling
authors.forename: Joanna L
authors.initials: JL
authors.lastname: Mimica
authors.forename: Barry J
authors.initials: BJ
authors.lastname: Pogson