Effects of Serine Acetyltransferase 2 (sat2) Haplotypes and Multiple Environmental Factors on Grain Protein Content and Yield-Related Traits in Bread Winter Wheat

Serine acetyltransferase 2 (sat2), rate-limiting for cysteine biosynthesis, is a candidate gene for grain protein content in durum wheat. We tested whether its intragenic variants are associated with protein content in bread winter wheat and how the effect depends on year, crop management, cultivar origin and other loci. Sixty-five cultivars were genotyped by Kompetitive Allele-Specific PCR for TDsat2.e9.1 (G>A, Gly325Ser) and TDsat2.i1.1 (G>T, intron 1). The variants were completely linked: only Hap1 (G; T; 32 cultivars) and Hap2 (A; G; 33 cultivars; the Chinese Spring reference haplotype) occurred. The 5913 observations (2021–2025; 16 year × management environments at one site) were analysed with a linear mixed model, the cultivar being the unit of replication. Hap1 exceeded Hap2 in protein content by 0.58% (95% CI 0.22–0.93; p = 0.0017; q = 0.014); the effect persisted with grain yield as a covariate and after adjustment for Glu-A1, Glu-D1 and 1BL.1RS, and haplotype frequencies were unrelated to cultivar origin and Rht-B1. Independently measured traits, including grain yield, did not differ. The effect kept its sign in all years but varied in size (p = 0.0013); no interaction with crop management was detected. The association requires confirmation in other collections.