A Puroindoline Mutigene Family Exhibits Sequence Diversity in Wheat and is Associated with Yield-Related Traits

Abstract

Kernel texture (grain hardness) is a leading quality characteristic of bread wheat (Triticum aestivum L.) as it dramatically influences the milling and processing properties, and consequently determines the classification and marketing of grain (Bhave and Morris 2008a, b). The word puroindoline is derived from the Greek word “puros” meaning wheat and “indoline” describing the indole ring of tryptophan (Gautier et al. 1994). Puroindolines, composed of puroindoline a and b, are amphipathic proteins of ca. 13,000 Da, and share homology with grain softness protein (GSP), purothionins, lipid transfer proteins, and other members of the prolamin super-family of proteins (Shewry and Halford 2002). Puroindoline proteins possess a characteristic tryptophan-rich domain and cysteine backbone; isoforms occur in the starchy endosperm of the Triticeae. Their secondary structure, determined by infrared and Raman spectroscopies, is comprised of approximately 30% ┙-helices, 30% ┚sheets, and 40% unordered structure at pH 7.4 in solution (Bihan et al. 1996). Puroindoline genes are present throughout the Triticeae tribe of the Poaceae (Gramineae), including wheat (Triticum sp.), rye (Secale sp.), barley (Hordeum sp.), and the wild relatives of wheat (Aegilops sp. and Triticum sp.). In Triticum aestivum, puroindolines exist as two expressed genes, Puroindoline a and Puroindoline b, and are located on the distal end of the short arm of chromosome 5 (5DS). An exception to this general situation lies with the tetraploid (AABB) wheats (T. turgidum), which include cultivated durum (ssp. durum). Apparently during the allotetraploidization formation of T. diccocoides, the wild ancestor of cultivated durum, both the Aand B-genome Puroindoline loci were eliminated due to transposable element insertion and two large deletions in the Hardness loci caused by illegitimate DNA recombination (Chantret et al. 2005). Consequently, hexaploid wheat, T. aestivum, possesses