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Improvement of Australian wheat grain functionality for breadmaking by introgression of novel high-molecular weight glutenin subunits into Australian cultivars

Roy, Nandita (2019) Improvement of Australian wheat grain functionality for breadmaking by introgression of novel high-molecular weight glutenin subunits into Australian cultivars. PhD thesis, Murdoch University.

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Bread wheat (Triticum aestivum) is one of the most important cereal crops in the world. It is an important component of human diet, chiefly as the main ingredient of the many available presentations of bread and noodles around the world. Wheat flour can produce dough with visco-elasticity properties, which is essential for bread making. Glutenin, a group of grain storage proteins, confers these visco-elasticity properties of dough. From the food production point of view, it is also called functional protein since it regulates end product quality. The breadmaking quality of Australian wheat cultivars can be enhanced by improving grain glutenin protein content. In this thesis, a range of HMW glutenin protein manipulation was conducted utilising introgression lines containing various alleles of the 1Ay high-molecular-weight glutenin subunit (HMW-GS) gene - which is silenced in current Australian wheat cultivars.

Wheat lines expressing two 1Ay HMW glutenin subunit alleles, 1Ay21* and 1AyT1, sourced from Italian hexaploid wheat germplasm, were successfully introgressed into a range of commercial Australian cultivars and advanced to the BC4F4 generation before further rounds of selfing were conducted to generate nearly-isogenic lines (NILs) carrying the introgressed genes. The F1 generation was developed by reciprocal crossing of the Australian cultivars with Ay donor wheat lines. MALDI-TOF mass spectrometry and SDS-PAGE were used to confirm introgression of the target 1Ay HMW-GS at each generation. Ay introgression NILs were developed through conventional breeding process that’s why may have change some unwanted gene effects on plants growth habit, grain and protein quality. The influence of different alleles of 1Ay on relative HMW GSs composition, HMW‐ /LMW‐GSs ratio, end‐use quality and grain yield has been evaluated from plants grown in small-scale glasshouse experiments and large-scale field trials. NIR and HPLC analyses were used for protein quantification. Extensograph, farinograph, and baking tests were carried out to evaluate dough and bread quality. Because of traditional breeding, there has been a greater possibility of passing unwanted genes in advance generations. That is why, the agronomic performance on 1Ay allele introgression lines have also been examined though large-scale field trial.

Expression of the novel Ay subunits in the NILs was stable in the Australian environment, as evidenced by the analysis results of grain from two years of field trials. No significant differences were observed between the reciprocal crossing NILs in terms of agronomic traits and grain protein attributes based on small scale quality test. However, introgression of the expressed 1Ay subunit genes led to an overall increase in protein and glutenin contents and resulted in significant increases of various end-product quality parameters. The level of changes was variable between the cultivar’s background. The active 1Ay21* subunit increased the amount of total protein by up to 15.4%, gluten content by up to 10%, glutenin content by up to 5%, the HMW-to-LMW-GS ratio and hence improved the dough extensibility (21%) without affecting the expression levels of the other subunits at Bonnie Rock background. On the other hand, expressed 1Ay21* increased polymeric protein (UPP%) by up to 14.3%, and improved dough strength by up to 28% respectively in Livingston background NILs. The Lincoln-derived Ay21* NILs showed increased grain protein% by up to 9% and grain yield up to 10%, indicating that protein content and grain yield can be increased simultaneously by introgressing the expressed Ay21* gene which shows great potential to ultimately increase Australian wheat productivity and value without increasing production costs. NILs at Lincoln bacground also showed increased UPP% by up to 24%, bread volume by up to 28%. The thesis also studied the allelic effect of expressed 1Ay gene that showed the two alleles have different levels of potential in improving grain, dough and baking qualities. On the other hand 1AyT1 subunit increased total grain protein by up to 9%, dough elasticity (Rmax) increased by up to 24%, reduced dough mixing time by up to 23% and increased bread volume by up to 2.4% (rapid-dough protocol) compared to the recurrent parent Livingston.

Since this study demonstrated significant variation between two expressed 1Ay alleles (Ay21* and AyT1) allele in influencing protein and end product quality another novel expressed Ay allele (AyT2) from an Israeli wheat tetraploid line also cloned and characterised. NILs were also generated in three Australian wheat cultivars Yitpi, Kukri and Livingston by integrating this novel expressed 1Ay HMW-GS, as for the other two Ay alleles. Result showed that the open reading frame of AyT2 is 1830 bp long and encodes a 608-residue polypeptide. 1AyT2 introgression NILs showed that UPP% increased by up to 50% and seed size increased by up to 36%.

The wheat lines developed in the current study and carrying the novel Ay HMW-GS genes have the potential to become new varieties or be used as parent lines by breeding programs to improve grain protein content and composition, thus improving viscoelastic properties of dough and therefore quality of baking products. Such improvement would in turn contribute toward enhancing the marketability of Australian wheat in global markets.

Item Type: Thesis (PhD)
Murdoch Affiliation: School of Veterinary and Life Sciences
United Nations SDGs: Goal 12: Responsible Consumption and Production
Supervisor(s): Ma, Wujun and Islam, Shahidul
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