Cloning and Characterization of a Critical Regulator for Preharvest Sprouting in Wheat

Abstract

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...

Maximizing the identification of QTL for pre-harvest sprouting resistance using seed dormancy measures in a white-grained hexaploid wheat population

“…The 3A chromosome was previously associated with a pre-harvest sprouting resistance QTL ), Qphs.pseru-3AS, reported by Liu et al (2008) and Liu and Bai (2010), although maps could not be cross-referenced. Liu et al (2013) cloned a gene from white-seeded wheat which they designated TaPHS1. Another gene on chromosome 3A reported to be involved in controlling seed dormancy and germination is TaMFT-A1, a homoeologue of MOTHER OF FT (Nakamura et al 2011;Lei et al 2013).…”

“…Interestingly, in wheat, these MFT homologs (TaMFT) colocalized with the seed dormancy QTL QPhs.ocs-3A.1 on chromosome 3A (Mori et al 2005). In a subsequent study, Liu et al (2013) cloned the gene TaPHS1 underlying the QTL Qphs.pseru-3AS on the short arm of chromosome 3A in white-seeded wheat using comparative and map-based cloning approaches. They discovered two single nucleotide polymorphisms (SNPs) in the promoter region and three SNPs in the TaPHS1 gene that altered pre-harvest sprouting resistance.…”

The Impact of Genetic Changes during Crop Domestication

“…Reducing seed coat thickness led to a concurrent reduction of seed coat impermeability during legume domestication [79]. Conversely, low seed dormancy levels can reduce seed viability and trigger preharvest sprouting, causing yield losses in cereals [80]. However, this is likely to be of greater concern to modern broad-acre farmers who are locked into a single, rapid, and timely harvesting process than to early agriculturalists who had the capacity to harvest their crop in a flexible manner on repeated occasions if necessary.…”

Identification of markers linked to genes for sprouting tolerance (independent of grain color) in hard white winter wheat (HWWW)

“…Nakamura et al (2011) studied sequence variation in the promoter region of a wheat gene designated TaMFT, and suggested that the difference in seed dormancy between moderately and highly PHS tolerant genotypes is controlled by this dormancy gene. Liu et al (2013) using comparative mapping and map-based cloning also isolated this locus (Qphs.pseru.3As) conditioning PHS tolerance. They renamed TaMFT (of Nakamura et al 2011) to TaPHS1 to better reflect the phenotype.…”

“…Liu et al found two mutations in TaPHS1 that changed wheat from a PHS tolerant to a susceptible genotype. A GT-to-AT mutation in TaPHS1 caused mis-splicing and further led to a premature stop codon that made the transcripts from the gene nonfunctional (Liu et al 2013). Liu et al (2013) suggested selection for positive alleles at this locus would be more predictive of PHS tolerance than seed color genes.…”