Insight into durum wheat Lpx-B1: a small gene family coding for the lipoxygenase responsible for carotenoid bleaching in mature grains

Abstract

BackgroundThe yellow colour of pasta products is one of the main criteria used by consumers to assess pasta quality. This character is due to the presence of carotenoid pigments in semolina. During pasta processing, oxidative degradation of carotenoid pigments occurs mainly due to lipoxygenase (LOX). In durum wheat (Triticum durum Desf.), two Lpx-1 genes have been identified on chromosome 4B, Lpx-B1.1 and Lpx-B1.2, and evidences have been reported that the deletion of Lpx-B1.1 is associated with a strong reduction in LOX activity in semolina. In the present study, we characterised the Lpx-B1 gene family identified in a durum wheat germplasm collection and related the distribution and expression of the Lpx-B1 genes and alleles to variations in LOX activity in the mature grains.ResultsIn addition to the already known Lpx-B1.1 and Lpx-B1.2 genes, a new gene was identified, Lpx-B1.3, along with three different Lpx-B1.1 alleles, Lpx-B1.1a, Lpx-B1.1b and the partially deleted Lpx-B1.1c. Screening of the germplasm collection showed that all of the genotypes have one of the three Lpx-B1.1 alleles, associated with either Lpx-B1.2 or Lpx-B1.3, thus showing that in this collection the two genes are alternatives. Therefore, based on Lpx-B1 distribution, three different haplotypes were distinguished: haplotype I, carrying Lpx-B1.3 and the Lpx-B1.1b allele; haplotype II carrying Lpx-B1.2 and the Lpx-B1.1a allele; and haplotype III carrying Lpx-B1.2 and the Lpx-B1.1c allele. Determination of Lpx-B1 transcript abundance and total LOX activity in mature grains revealed differences among these three haplotypes: haplotypes I, II and III showed high, intermediate and low levels, respectively, of functional Lpx-B1 transcripts and enzymatic activity.ConclusionsIn this germplasm collection, the Lpx-B1 gene family accounts for most of the total LOX activity in the mature grains. Information on these Lpx-B1 haplotypes provides significant improvement for prediction of LOX-1 activity levels in mature grains, and will therefore help in breeding programmes aimed at selection of new durum wheat genotypes with higher carotenoid contents in their end products.

The colours of durum wheat: a review

“…This suggests that the LOX-1 isoform might have a major role in oxidation of carotenoid pigments during pasta processing. This hypothesis is supported by evidence highlighting the existence of a major QTL for total LOX activity on chromosome 4BS, where three copies of the Lpx-1 gene, Lpx-B1.1, Lpx-B1.2 and Lpx-B1.3, along with three different Lpx-B1.1 alleles, Lpx-B1.1a, Lpx-B1.1b and Lpx-B1.1c, have been mapped Hessler et al 2002;Carrera et al 2007;Verlotta et al 2010). The Lpx-B1 genes/alleles comprise seven exons and six introns, with the exception of the Lpx-B1.1c allele, which has a large central deletion and most probably encodes a non-functional LOX-1 isoform (Verlotta et al 2010).…”

“…Recently, in hexaploid wheat, Geng et al (2012) characterised the full-length genomic DNA sequence of a LOX gene (designated as Lox-B1) ( Table 1) that is located on chromosome 4BS and shows high identity (98.6%) with the durum wheat Lpx-B1.2 gene, previously reported by Verlotta et al (2010). Two complementary, dominant sequence-tagged site markers, LOX16 and LOX18, were developed based on the single nucleotide polymorphism of two alleles at the Lox-B1 locus, with the amplification of 489-bp and 791-bp fragments in cultivars with higher and lower LOX activities, respectively.…”

“…For carotenoid degradation, an important family of oxidative enzymes is responsible for the loss of the yellow colour during pasta making-the lipoxygenases (LOXs) (McDonald 1979;Trono et al 1999;Pastore et al 2000;De Simone et al 2010;Verlotta et al 2010). The LOXs are a class of non-heme iron enzymes containing dioxygenase activities and catalysing the positional and specific dioxygenation of polyunsaturated fatty acids with 1,4-cis,cis pentadiene structures, to produce the corresponding hydroperoxides.…”

“…The Lpx-1 and Lpx-3 genes encode the LOX-1 and LOX-2 isoforms, respectively, and they are located on chromosome 4, whereas the Lpx-2 gene that encodes the LOX-3 isoform is on chromosome 5 (Manna et al 1998;Carrera et al 2007;Garbus et al 2009;De Simone et al 2010;Feng et al 2010;Verlotta et al 2010). Molecular studies of Lpx in developing durum wheat kernels have shown different transcript levels, with Lpx-1 transcripts being the most abundant in mature grain .…”

“…Screening of a large collection of germplasm has revealed that all of the durum wheat genotypes that carry the Lpx-B1.1c allele also have very low LOX activity in the grain (Verlotta et al 2010). Therefore, selection and fixing of this allele (Table 1) in all breeding lines will contribute to significantly reduced pigment loss during pasta processing and, consequently, to improvement of the aesthetic and nutritional qualities of the pasta products.…”