Using the Hexaploid Nature of Wheat To Create Variability in Starch Characteristics

Abstract

In hexaploid crops, such as bread wheat, it should be possible to fine-tune phenotypic traits by identifying wild-type and null genes from each of the three genomes and combining them in a calculated manner. Here, we demonstrate this with gene combinations for two starch synthesis genes, SSIIa and GBSSI. Lines with inactive copies of both enzymes show a very dramatic change in phenotype, so to create intermediate phenotypes, we used marker-assisted selection to develop near-isogenic lines (NILs) carrying homozygous combinations of null alleles. For both genes, gene dosage effects follow the order B > D ≥ A; therefore, we completed detailed analysis of starch characteristics for NIL 3-3, which is null for the B-genome copy of the SSIIa and GBSSI genes, and NIL 5-5, which has null mutations in the B- and D-genome-encoded copies of both of these genes. The effects of the combinations on phenotypic traits followed the order expected on the basis of genotype, with NIL 5-5 showing the largest differences from the wild type, while NIL 3-3 characteristics were intermediate between NIL 5-5 and the wild type. Differences among genotypes were significant for many starch characteristics, including percent amylose, chain length distribution, gelatinization temperature, retrogradation, and pasting properties, and these differences appeared to translate into improvements in end-product quality, since bread made from type 5-5 flour showed a 3 day lag in staling.

Longer Bread Shelf-Life and Improved Noodle-Making Properties Imparted by a Novel Wheat Genotype Are Stable in Different Genetic Backgrounds

“…The distribution of starch branch chains in 5-5 NILs shifted to a shorter length (Figure ), and on average, the ratio of DP 6-10 chains was 3.3 and 3.2% higher in the MK 5-5 NIL and the SK 5-5 NIL than those of the associated recurrent parents (Table ). Thus, a reduced amylose content and an increased proportion of short chains of amylopectin were clearly apparent in type 5-5 NILs, and these starch characteristics are consistent with our previous report …”

“…MK and SK differ in grain qualities, including protein quality, grain hardness, and related traits; MK is a hard type used mainly for bread-making, while SK is a soft type used for making white salted noodles (Udon noodles). Type 5-5 (lacking GBSSI-B1 and -D1 and SSIIa-B1 and -D1) NILs of each recurrent parent were developed as previously described (Inokuma et al) . For each cultivar, near-isogenic waxy (Wx) lines having inactive alleles for all GBSSI genes and near-isogenic high-amylose (HA) lines having inactive alleles for all SSIIa genes were developed by backcrossing to each recurrent parent at least 6 times.…”

“…SK and SK 5-5, as well as our previously described lines MD-B004 and MD-B004 5-5, were analyzed for noodle-making quality, using 60% extraction flours prepared from grain samples harvested in 2015. The flour samples from MD-B004 and MD-B004 5-5 are the same as previously described (Inokuma et al) . White salted noodles were prepared from 500 g of flour (based on 13.5% moisture content).…”

“…Of these, we previously developed three near-isogenic lines (NILs) based on Morikei D-B004 (MD-B004) including NIL type 1-1 (expressing all six enzymes), NIL type 3-3 (lacking GBSSI-B1 and SSIIa-B1), and NIL type 5-5 (lacking GBSSI-B1 and -D1 and SSIIa-B1 and -D1). Changes of starch structure and properties of the type 3-3 and type 5-5 NILs were compared with type 1-1 NIL . Larger decreases in amylose levels and larger changes in chain length distribution (CLD) profiles were observed in type 5-5 than in type 3-3.…”

Combining mutations at genes encoding key enzymes involved in starch synthesis affects the amylose content, carbohydrate allocation and hardness in the wheat grain

“…Because bread wheat is hexaploid, independent mutations at each of the three homeoloci GBSSI‐A1 , GBSSI‐B1 and GBSSI‐D1 have to be combined into a single line by conventional breeding (Nakamura et al ., ; Slade et al ., ). Depending on their content of GBSSI mutations, the proportion of amylose in the endosperm starch has been successfully reduced from 25% to 30% all the way to 0% (Inokuma et al ., ). High amylose content alleles are also available in a number of cereals, including wheat.…”