Title: Segregation analysis indicates that Puroindoline b-2 variants 2 and 3 are allelic in Triticum aestivum L. and that a revision to Puroindoline b-2 gene symbolization is indicated Authors
Submitted to: Journal of Cereal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 24, 2012
Publication Date: January 2, 2013
Citation: Geng, H.W., Beecher, B.S., Pumphrey, M., He, Z.H., Morris, C.F. 2013. Segregation analysis indicates that Puroindoline b-2 variants 2 and 3 are allelic in Triticum aestivum L. and that a revision to Puroindoline b-2 gene symbolization is indicated. Journal of Cereal Science. 57:61-66. Interpretive Summary: Grain hardness is a leading determinant of both milling performance and end-product quality of bread wheat, and is used for market classification of the grain. Based on grain hardness, wheat is typically classified into soft, hard, and durum (T. turgidum ssp. durum) classes. The molecular basis of the distinction between soft and hard classes results from the puroindoline genes at the hardness locus, located on chromosome 5DS in common wheat and includes Puroindoline a (Pina-D1) and Puroindoline b (Pinb-D1). Recently a new Puroindoline-like gene (Puroindoline b2) was reported. To date, the function of these new Puroindoline b2 variants is still unknown, although it has been indicated that the Pinb-2 variants were expressed at less than 10% of the levels of transcripts encoding Pina-D1 and Pinb-D1, and the Pinb-B2v3 allele was associated with preferable grain yield traits compared to the Pinb-B2v2 allele in bread wheat. There is a question as to whether Pinb-2v2 and Pinb-2v3 are paralogs or orthologs, even though past studies indicated Pinb-2v2 and Pinb-2v3 were always reciprocally present in all different common and durum wheat cultivars. In this study, a total of 480 lines, derived from three F2 populations IDO686 × HT080091, Bullseye × WA8123 and Bullseye × BR7030 were used to investigate the segregation ratios of Puroindoline D1 alleles and Pinb-2 variants 2 and 3.
Technical Abstract: Conclusive genetic and kernel texture phenotypic relationships between Puroindoline b 2 variant sequences 2 and 3 have not been fully established in wheat (Triticum aestivum L.). In the present study, a total of 480 F2 plants, derived from three hard spring wheat populations WSU.HRS1×WSU.HWS1 (abbreviated HRS/HWS, n = 120), Bullseye × WA8123 (B eye/WA, n = 240) and Bullseye × BR7030 (B-eye/BR, n = 120) were used to test the segregation ratios of the Puroindoline b-2 (Pinb-2) variant 2 and 3 forms of the gene. Chi square analysis indicated that Pinb-2 variants 2 and 3 in all three F2 populations segregated as a single bi-allelic locus, wherein the segregation ratios fit well with a Mendelian 1:2:1 ratio ( 2 values to reject a single gene model, H0, were not significant with P = 0.91, 0.86, 0.82 and 0.77 for the HRS/HWS, B-eye/WA and B-eye/BR populations, and the averaged data, respectively). As further corroboration of previous studies, the analysis of Puroindoline a-D1 (Pina-D1) and Puroindoline b-D1 (Pinb-D1) returned non-significant 2 values against rejection of a single gene model (P = 0.88, 0.74 and 0.66 for the Red/White, B-eye/WA populations, and the averaged data, respectively). Using 448 of the 480 wheat plants derived from these three F2 populations, the average SKCS hardness index of plants that were homozygous for Pinb-2 variant 2 vs. those homozygous for variant 3 was not significantly different (67.5 vs. 67.9, P = 0.92). The relationship between Pin-D1 hardness alleles and kernel texture was also analyzed. Results indicated that homozygous progeny plants with Pina-D1b/Pinb -D1a were on average 10.0 Single Kernel Characterization System (SKCS) hardness index units harder than those carrying the Pina-D1a/Pinb-D1b haplotype. In conclusion, Pinb-2 variants 2 and 3 are allelic and exert little if any effect on kernel texture in T. aestivum. According to the recommended rules for gene symbolization in wheat, the designation of Pinb-2v2 and Pinb-2v3 should be changed Pinb-B2a and Pinb-B2b, respectively. Given the present results and the accumulating body of research, we further propose that Pinb-2 variants 1 and 4 of Chinese Spring be designated Pinb-D2a and Pinb A2a, respectively.