Molecular insights on the origin and development of waxy genotypes in major crop plants

Starch is a significant ingredient of the seed endosperm with commercial importance in food and industry. Crop varieties with glutinous (waxy) grain characteristics, i.e. starch with high amylopectin and low amylose, hold longstanding cultural importance in some world regions and unique properties for industrial manufacture. The waxy character in many crop species is regulated by a single gene known as GBSSI (or waxy), which encodes the enzyme Granule Bound Starch Synthase1 with null or reduced activity. Several allelic variants of the waxy gene that contribute to varying levels of amylose content have been reported in different crop plants. Phylogenetic analysis of protein sequences and the genomic DNA encoding GBSSI of major cereals and recently sequenced millets and pseudo-cereals have shown that GBSSI orthologs form distinct clusters, each representing a separate crop lineage. With the rapidly increasing demand for waxy starch in food and non-food applications, conventional crop breeding techniques and modern crop improvement technologies such as gene silencing and genome editing have been deployed to develop new waxy crop cultivars. The advances in research on waxy alleles across different crops have unveiled new possibilities for modifying the synthesis of amylose and amylopectin starch, leading to the potential creation of customized crops in the future. This article presents molecular lines of evidence on the emergence of waxy genes in various crops, including their genesis and evolution, molecular structure, comparative analysis and breeding innovations.

Grain Yield Performance and Quality Characteristics of Waxy and Non-Waxy Winter Wheat Cultivars under High and Low-Input Farming Systems

Waxy starch with a modified amylose-to-amylopectin ratio is desired for a range of applications in food and non-food industries; however, yield performance and grain quality characteristics of waxy wheat cultivars are usually inferior in comparison to advanced non-waxy cultivars. In this study, we compared waxy (‘Eldija’, ‘Sarta’) and non-waxy (‘Skagen’, ‘Suleva DS’) winter wheat cultivars grown under high and low-input farming systems over two cropping seasons by evaluating their yield and grain quality, including flour, dough, and starch physicochemical properties. The yield of waxy cv. ‘Sarta’ was significantly lower compared to the non-waxy cultivars across all trials; however, waxy cv. ‘Eldija’ had a similar yield as non-waxy cultivars (except under high-input conditions cv. ‘Skagen’). Moreover, no significant differences were observed between protein and gluten content of waxy and non-waxy cultivars. Low amylose content typical for waxy wheat cultivars highly correlated (r ≥ 0.8) with lower falling number, flour yield and sedimentation values, lower nitrogen % used for grain, higher flour water absorption and flour particle size index. In general, properties dependent on starch structure demonstrated consistent and significant differences between both starch types. The prevailing heat waves during the grain filling period decreased grain test weight but increased protein and gluten content and caused gluten to be weaker. Dough development time at these conditions became longer, dough softening lowered and starch content decreased, but A-starch, starch peak and final viscosity values increased. Low-input farming had a negative effect on grain yield, grain nitrogen uptake and grain test weight but increased phosphorus content in grain. The unique dough mixing properties of waxy cultivar ‘Eldija’ suggest that it could be used in mixtures along with non-waxy wheat for dough quality improvement.

The potential of fiber-depleted starch concentrate produced through air currents assisted particle separation of barley flour in bio-ethanol production

Isolation of fiber concentrate enriched in β-glucan from barley flour via air currents assisted particle separation (ACAPS) generates an underutilized by-product stream, starch concentrate. Since barley starch concentrate (BSC) is depleted in soluble fibre, we examined the enzyme requirements for its hydrolysis and subsequent fermentation. Lower doses of a common raw starch hydrolyzing enzyme (STARGEN™ 002) effectively hydrolyzed BSC, achieving similar hydrolysis kinetics to the wheat benchmark. Hydrolysis of BSC did not require further enzyme supplementation, which is required for optimal wheat hydrolysis. This likely resulted from the smaller particle size of BSC relative to wheat feedstocks. Interestingly, simultaneous saccharification and fermentation of BSC using a 0.25X dose of STARGEN™ 002 alone enabled efficient ethanol production, though a requirement for phosphorus supplementation was identified. This study proposes a biorefining strategy that supports the generation of a value-added co-product, starch concentrate, while significantly reducing the enzyme requirements for bioethanol production.

The quality of rice wine influenced by the crystal structure of rice starch

Normal rice wine (NRW) and waxy rice wine (WRW) were fermented to study the relationship between the structure of starch as well as the taste and texture of rice wine. The total starch content of NRW decreased to 21.2%, and that of WRW decreased to 15.6%. The water-soluble sugar content of NRW increased to 169.3, and that of WRW increased to 194.4 mg/g. The ethanol content of NRW increased to 6.5%, and that of WRW increased to 8.9%. These changes indicated that WRW exhibited higher quality than NRW. Sweetness was negatively correlated with total starch content and positively correlated with ethanol content. Starch molecules were degraded by enzymolysis, thereby enhancing crystallinity. The size of starch particle was negatively correlated with crystallinity, whereas the chewiness and gumminess of vinasse (fermented rice grains) were positively correlated with the size of starch particle and negatively correlated with crystallinity. The higher degrees of chewiness and gumminess of vinasse render the texture of WRW superior to that of NRW. The results indicated that WRW is superior to NRW in taste and texture because of the difference in starch structure.

Effect of waxy (Low Amylose) on Fungal Infection of Sorghum Grain

Loss of function mutations in waxy, encoding granule bound starch synthase (GBSS) that synthesizes amylose, results in starch granules containing mostly amylopectin. Low amylose grain with altered starch properties has increased usability for feed, food, and grain-based ethanol. In sorghum, two classes of waxy (wx) alleles had been characterized for absence or presence of GBSS: wx(a) (GBSS(-)) and wx(b) (GBSS(+), with reduced activity). Field-grown grain of wild-type; waxy, GBSS(-); and waxy, GBSS(+) plant introduction accessions were screened for fungal infection. Overall, results showed that waxy grains were not more susceptible than wild-type. GBSS(-) and wild-type grain had similar infection levels. However, height was a factor with waxy, GBSS(+) lines: short accessions (wx(b) allele) were more susceptible than tall accessions (undescribed allele). In greenhouse experiments, grain from accessions and near-isogenic wx(a), wx(b), and wild-type lines were inoculated with Alternaria sp., Fusarium thapsinum, and Curvularia sorghina to analyze germination and seedling fitness. As a group, waxy lines were not more susceptible to these pathogens than wild-type, supporting field evaluations. After C. sorghina and F. thapsinum inoculations most waxy and wild-type lines had reduced emergence, survival, and seedling weights. These results are valuable for developing waxy hybrids with resistance to grain-infecting fungi.

Toward underlying reasons for rice starches having low viscosity and high amylose: physiochemical and structural characteristics

BACKGROUND

To understand the reasons for low starch viscosity in rice variety Q11 (Qing-lu-zhan 11), the physiochemical and structural characteristics of flours and starches were investigated and compared with another rice cultivar with similar high amylose but normal viscosity.

RESULTS

Our results showed that residual α-amylase activity and proteins were not the major causes of low starch viscosity in Q11 rice. Homogeneous small granule size and lower swelling power of high-amylose Q11 rice starches was one reason for the low swelling volume and thus the low pasting property. Q11 starch paste contained some partially swollen granules, which could increase the fluidity and thus cause the low paste viscosity. The small gelatinization enthalpy might be due to the lower crystallinity in Q11 starches. Moreover, Q11 starches consisted of more amylose with short chains, but also amylopectin with fewer short chains (DP 11-21) and more long chains (DP 22-54), which might be other important factors contributing to the low viscosity of Q11 starches.

CONCLUSION

These data can add to our understanding of the relationships between low viscosity and physiochemical properties, and will be helpful in elucidating the underlying mechanism of formation of low starch viscosity, as well as applications for low-viscosity rice starches.

A laboratory protocol for determining glucose and maximum ethanol production from wheat grain: application to a complete genetic set of near-isogenic waxy lines

A laboratory protocol was developed to assess glucose and ethanol yields from wheat. The impact of the analyzed wholemeal flour quantity and the saccharification on the amount of released glucose was estimated. The whole process including the analytical methods (glucose and ethanol) was repeatable and reproducible. This protocol was used to assess the glucose and ethanol yields of six varieties and of a complete set of hexaploid near-isogenic waxy lines of cv. Trémie grown in three locations. As compared to the normal line of Trémie, double null (AnBnD) and triple null (nAnBnD) isogenic lines showed a low Hagberg falling number (218, 65, and 63 s, respectively), a higher grain protein content (10.7, 11.5, and 12.1% DM, respectively), a lower glucose yield (728, 703, and 707 kg/t, respectively), and a lower ethanol yield (463, 453, and 452 L/t, respectively). These values indicate a strong involvement of alleles encoded at Wx-B1 and Wx-D1 loci in grain composition.

Starch waxiness in hexaploid wheat (Triticum aestivum L.) by NIR reflectance spectroscopy

Wheat (Triticum aestivum L.) breeding programs are currently developing varieties that are free of amylose (waxy wheat), as well as genetically intermediate (partial waxy) types. Successful introduction of waxy wheat varieties into commerce is predicated on a rapid methodology at the commodity point of sale that can test for the waxy condition. Near-infrared (NIR) reflectance spectroscopy, one such technology, was applied to a diverse set of hard winter (hexaploid) wheat breeders' lines representing all eight genotypic combinations of alleles at the wx-A1, wx-B1, and wx-D1 loci. These loci encode granule-bound starch synthase, the enzyme responsible for amylose synthesis. Linear discriminant analysis of principal components scores 1-4 was successful in identifying the fully waxy samples at typically greater than 90% accuracy; however, accuracy was reduced for partial and wild-type genotypes. It is suggested that the spectral sensitivity to waxiness is due to (1) the lipid-amylose complex which diminishes with waxiness, (2) physical differences in endosperm that affect light scatter, or (3) changes in starch crystallinity.