Sprouting of grains in mature spikes before harvest is a major problem in wheat (Triticum aestivum) production worldwide. We cloned and characterized a gene underlying a wheat quantitative trait locus (QTL) on the short arm of chromosome 3A for preharvest sprouting (PHS) resistance in white wheat using comparative mapping and map-based cloning. This gene, designated TaPHS1, is a wheat homolog of a MOTHER OF FLOWERING TIME (TaMFT)-like gene. RNA interference-mediated knockdown of the gene confirmed that TaPHS1 positively regulates PHS resistance. We discovered two causal mutations in TaPHS1 that jointly altered PHS resistance in wheat. One GT-to-AT mutation generates a mis-splicing site, and the other A-to-T mutation creates a premature stop codon that results in a truncated nonfunctional transcript. Association analysis of a set of wheat cultivars validated the role of the two mutations on PHS resistance. The molecular characterization of TaPHS1 is significant for expediting breeding for PHS resistance to protect grain yield and quality in wheat production.
WHEAT is a staple food crop for .40% of the world's population and provides .20% of calories and proteins for humans (Gill et al. 2004). Preharvest sprouting (PHS) in wheat (physiologically mature grains germinating in spikes before harvest) causes significant loss in grain yield and quality, particularly in regions with prolonged wet weather during the harvest season. Direct annual losses caused by PHS approach $1 billion dollars worldwide (Black et al. 2006).Resistance to PHS in wheat is a complex trait that is affected by both genotype and environment (Imtiaz et al. 2008). Grain color and seed dormancy have long been regarded as two major factors affecting PHS resistance (Gfeller and Svejda 1960;Bewley 1997;Groos et al. 2002). White grain wheat is usually more susceptible to PHS than red grain wheat (Gale and Lenton 1987;Groos et al. 2002;Himi et al. 2002). Demand for white grain wheat is increasing rapidly in many countries because of consumer preferences, higher flour yield, and better enduse quality; therefore, improving resistance to PHS in white wheat is imperative for successful production in environments where PHS occurs.Seed dormancy is another important trait of PHS resistance (Bewley 1997;Mares et al. 2005;Sussman and Phillips 2009). Adequate seed dormancy can reduce or block PHS during harvest seasons, but dormancy breaks down during seed storage so seeds germinate uniformly after sowing. Several other factors have been proposed as potential contributors to overall PHS resistance in field conditions, including germination-inhibitory substances residing in chaff tissue (Derera and Bhatt 1980;Gatford et al. 2002), physical barriers to water penetration in a spike, and spike morphology such as structure and erectness of wheat spikes, openness of florets, and tenacity of glumes (King and Richards 1984). The degree to which these factors contribute to the levels of wheat PHS resistance remains unknown.To date, PHS resistance genes have not b...