Sequencing of the Pinb-2 Locus in Triticum monococcum and Triticum urartu

Recently, four novel genes named Pinb-2, with 57-60% sequence similarity with wild-type allele Pinb-D1a coding for grain-hardness related puroindoline B have been shown to occur on homoeologous group 7 chromosomes in bread wheat (Triticum aestivum). In the present report, T. monococcum ssp. monococcum (A(m) genome) revealed a Pinb-2 gene with a poly-G tract and an in-frame TAG stop codon at the 5' terminus of the coding DNA sequence. The stop codon was observed in 53 accessions of different geographic origins, suggesting that Pinb-2 in 'monococcum' wheat is unlikely to be expressed. By contrast, the coding DNA sequence of Pinb-2 in T. urartu (A(u) genome) was found to be 99% identical to its counterpart on chromosome 7AL in bread and durum (T. turgidum ssp. durum) wheat. Moreover, a sequence very similar to "urartu" Pinb-2 was found in tetraploid wheat T. timopheevii and hexaploid wheat T. zhukovskyi. This latter species exhibited an additional Pinb-2 pseudogene inherited from T. monococcum. The results are discussed in relation to the lineage of T. zhukovskyi and the potential role of Pin-b2 on kernel texture.