Physical mapping of puroindoline b-2 genes and molecular characterization of a novel variant in durum wheat (Triticum turgidum L.)

The puroindoline genes ( Pina and Pinb ) are the functional components of the common or bread wheat ( Triticum aestivum L.) grain hardness locus that are responsible for kernel texture. In this study, four puroindoline b - 2 variants were physically mapped using nulli-tetrosomic lines of bread wheat cultivar Chinese Spring and substitution lines of durum wheat ( Triticum turgidum L.) cultivar Langdon. Results indicated that Pinb - 2v1 was on 7D of Chinese Spring, Pinb - 2v2 on 7B of Chinese Spring, Pinb - 2v3 on 7B of Chinese Spring and Langdon, and Pinb - 2v4 on 7A of Chinese Spring and Langdon. A new puroindoline b - 2 variant, designated Pinb - 2v5 , was identified at the puroindoline b - 2 locus of durum wheat cultivar Langdon, with a difference of only five single nucelotide polymorphisms compared with Pinb - 2v4 . Sequencing results indicated that, in comparison with the Pinb - 2v3 sequence (AM99733 and GQ496618 with one base-pair modification of G to T at 6th position, designated Pinb - 2v3a ) in bread wheat cultivar Witchta, the coding region of Pinb - 2v3 in 12 durum wheat cultivars had a single nucleotide change from T to C at the 311th position, resulting in a corresponding amino acid change from valine to alanine at the 104th position. This new allele was designated Pinb - 2v3b . The study of puroindoline b - 2 gene polymorphism in CIMMYT and Italian durum wheat germplasm and discovery of a novel puroindoline b - 2 variant could provide useful information for further understanding the molecular and genetic basis of kernel hardness and illustrating gene duplication events in wheat.