Expansion of the gamma-gliadin gene family in <it>Aegilops</it> and <it>Triticum</it>

• Main Authors: Goryunova Svetlana V, Salentijn Elma MJ, Chikida Nadejda N, Kochieva Elena Z, van der Meer Ingrid M, Gilissen Luud JWJ, Smulders Marinus JM
• Format: Article
• Language: English
• Published: BMC 2012-11-01
• Series: BMC Evolutionary Biology
• Subjects: Gamma-gliadin; Wheat; <it>Triticum</it>; <it>Aegilops</it>; Multigene family; Evolution
• Online Access: http://www.biomedcentral.com/1471-2148/12/215

<p>Abstract</p> <p>Background</p> <p>The gamma-gliadins are considered to be the oldest of the gliadin family of storage proteins in <it>Aegilops/Triticum</it>. However, the expansion of this multigene family has not been studied in an evolutionary perspective.</p> <p>Results</p> <p>We have cloned 59 gamma-gliadin genes from <it>Aegilops</it> and <it>Triticum</it> species (<it>Aegilops caudata</it> L., <it>Aegilops comosa</it> Sm. in Sibth. & Sm., <it>Aegilops mutica</it> Boiss., <it>Aegilops speltoides</it> Tausch, <it>Aegilops tauschii</it> Coss., <it>Aegilops umbellulata</it> Zhuk., <it>Aegilops uniaristata</it> Vis., and <it>Triticum monococcum</it> L.) representing eight different genomes: A^m, B/S, C, D, M, N, T and U. Overall, 15% of the sequences contained internal stop codons resulting in pseudogenes, but this percentage was variable among genomes, up to over 50% in <it>Ae. umbellulata</it>. The most common length of the deduced protein, including the signal peptide, was 302 amino acids, but the length varied from 215 to 362 amino acids, both obtained from <it>Ae. speltoides.</it> Most genes encoded proteins with eight cysteines. However, all <it>Aegilops</it> species had genes that encoded a gamma-gliadin protein of 302 amino acids with an additional cysteine. These conserved nine-cysteine gamma-gliadins may perform a specific function, possibly as chain terminators in gluten network formation in protein bodies during endosperm development. A phylogenetic analysis of gamma-gliadins derived from <it>Aegilops</it> and <it>Triticum</it> species and the related genera <it>Lophopyrum</it>, <it>Crithopsis</it>, and <it>Dasypyrum</it> showed six groups of genes. Most <it>Aegilops</it> species contained gamma-gliadin genes from several of these groups, which also included sequences from the genera <it>Lophopyrum, Crithopsis,</it> and <it>Dasypyrum.</it> Hordein and secalin sequences formed separate groups.</p> <p>Conclusions</p> <p>We present a model for the evolution of the gamma-gliadins from which we deduce that the most recent common ancestor (MRCA) of <it>Aegilops/Triticum-Dasypyrum-Lophopyrum-Crithopsis</it> already had four groups of gamma-gliadin sequences, presumably the result of two rounds of duplication of the locus.</p>