Prevalence of Puroindoline Grain Hardness Genotypes among Historically Significant North American Spring and Winter Wheats

Abstract

Grain hardness (“hard” or “soft” kernel texture) is the single most important trait in determining the utilization and marketing of wheat (Triticum aestivum L.). Puroindoline a and b proteins represent the molecular basis for this trait. This study surveyed the prevalence of puroindoline hardness mutations (alleles) among North American spring and winter wheat varieties with emphasis on those that are historically important. Each variety was assessed for kernel texture using the Single Kernel Characterization System; Hardness alleles were defined by puroindoline gene sequence and the presence or absence of puroindoline a protein on polyacrylamide gels. A total of 90 spring wheats were examined: nine were soft and possessed wild‐type (“soft”) puroindoline sequences, 10 were mixed hardness, and the remaining 71 were uniformly hard. Of these hard spring wheats, 18 carried the Pina‐D1b hardness allele (null for puroindoline a protein), 47 the Pinb‐D1b allele (Gly‐46–Ser‐46), and four the Pinb‐D1c allele (Leu‐60–Pro‐60). Two hard spring wheats possessed a new allele, designated Pinb‐D1e, which involves a single nucleotide change in Trp‐39 to a “stop” codon. Lastly, among the spring wheats, a new hardness allele was found in the hard component of the variety ‘Utac’ which was mixed. This allele, Pinb‐D1f, also involved a single nucleotide change such that Trp‐44 became a “stop” codon. A total of 62 winter wheat varieties were examined, of which five were soft and three were of mixed hardness. Of interest, the three mixed hardness wheats were ‘Turkey’, ‘Kharkof’, and ‘Weston’. The hard component of each carried the Pinb‐D1b allele. Of the 54 remaining wheats, all of which were hard, all but two carried this same Pinb‐D1b allele. ‘Chiefkan’ winter wheat carried the same Pinb‐D1e allele as ‘Canadian Red’ and ‘Gehun’ spring wheats. ‘Andrews’ hard red winter wheat possessed a new allele, designated Pinb‐D1g, which was a single nucleotide change in Cys‐56 to a “stop” codon. In conclusion, hard grain phenotype results from one of various mutations in either of the puroindoline proteins. To‐date, seven hardness alleles have been discovered and characterized in hexapoid wheat. All but one occur in the puroindoline b gene coding sequence and result from single nucleotide changes. These molecular markers are useful in characterizing lineages and analyzing ancestral relationships.

Recurrent Deletions of Puroindoline Genes at the GrainHardnessLocus in Four Independent Lineages of Polyploid Wheat

“…The situation may be more severe when polyploid plants are under abiotic stress, such as heat and drought during grain filling, which adversely affects endosperm development. Point mutations in Pinb can liberate the PIN proteins from binding to the starch granule surface and cause significant difference in grain texture Morris, 1997, 1998;Morris et al, 2001); however, the PIN proteins with the AAI activity remain in the endosperm cells. Therefore, deletion of Pina-Pinb genes provides the most efficient mechanism to reduce AAI activity and is the least detrimental because they are structural genes.…”

“…Of the 40 T. aestivum accessions, 37 showed a conserved haplotype structure for Pina and Pinb in the D genome (Ha-D) and, as expected, a null haplotype for the A and B genomes. Of the 18 hard wheat cultivars that do not express the PINA protein (Morris et al, 2001), 'Red Egyptian', 'Sea Island', and 'Komar' showed the null haplotype at Ha-D. Further probing with BGGP and Gsp detected three copies in 'Sea Island' and 'Komar', but only two in 'Red Egyptian' (Fig. 4).…”

Puroindoline allele diversity in Canadian and northern US hard spring wheat varieties differing in kernel hardness

“…Numerous separate single nucleotide changes within Pina-D1 and Pinb-D1 (alleles Pinb-D1b, Pinb-D1c, etc.) result in high kernel hardness (Giroux et al 2000;Lillemo and Morris 2000;Morris et al 2001;Xia et al 2005;Chen et al 2006;Ram et al 2005). Grain softness proteins (GSPs) are closely related to puroindolines (Gautier et al 2000) and the grain softness protein-1 gene (Gsp-D1) is closely linked to the Ha locus in wheat (Jolly et al 1996) and T. monococcum L. (Gsp-Am1).…”

“…Based on these studies, at least 25 alleles at the Pinb-D1 locus have been reported (Lillemo and Morris 2000;Morris et al 2001;Tranquilli et al 2002;Ram et al 2005;Xia et al 2005;Chen et al 2006Chen et al , 2007Bhave and Morris 2008), but the Pinb-D1b allele is the most prevalent allele in US, Norwegian, Japanese, South Korean, Indian, and Chinese varieties (Chen et al 2006;Lillemo and Morris 2000;Morris et al 2001;Ikeda et al 2005;Ram et al 2005;Xia et al 2005). Unlike the Pinb-D1 locus, only a few mutations conferring kernel hardness have been reported at Pina-D1.…”

“…The SCKS crushes individual kernels and uses algorithms based on the force-deformation data to quantify wheat endosperm texture as a HI (Gaines et al 1996;Morris et al 2001). A higher HI is indicative of greater force required to crush a seed and a strong negative correlation (average r 0(0.94) exists between SKCS HI and particle size index (PSI).…”