Occurrence of puroindoline alleles in Chinese winter wheats

Grain hardness is one of the most important characters that determine the end-use quality of bread wheat (Triticum aestivum L.). Mutations in genes encoding either puroindoline a (Pina) or b (Pinb) have been associated with hard grain texture, i.e., Pina null at Pina-D1 or seven mutations at Pinb-D1. In this study, the diversity of puroindoline alleles in 251 Chinese winter wheat cultivars and advanced lines from four major autumn-planted wheat regions were investigated. Among the examined cultivars, 79 were classified as soft, while 53 were mixed in hardness, and 119 were uniformly hard. Of these hard winter wheats, three of the seven reported mutation types were observed, with Pina-D1a/Pinb-D1b being the dominant type for hard texture; 91 genotypes carried this allele. Sixteen genotypes had the Pina-D1b allele, and two genotypes had the PinbD1d allele. A new mutation, designated as Pinb-D1p, was detected in 10 hard genotypes, with a single nucleotide (A) deletion corresponding to position 42 in the amino acid sequence of puroindoline b, involving a lysine (K) to asparagine (N) change, and leading to a shift in the open reading frame (ORF). This deletion disrupts the last part of the tryptophanrich domain, changing it from KWWK to NGGR, which is considered essential for the lipid-binding activity of this protein, and results in a stop codon corresponding to position Pro-60 in the amino acid sequence. The characterization of different hardness alleles provides useful information in understanding the mechanism underlying the formation of endosperm hardness while providing breeders the means of manipulating this important trait.