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Title: Investigating Contradictory Findings Related to Auxin and Thousand-Grain Weight 6 (TGW6) Gene and their Relationship with Grain Weight in Wheat
Contributor(s): Kabir, Muhammed Rezwan  (author); Nonhebel, Heather  (supervisor)orcid ; Backhouse, David  (supervisor)orcid ; Winter Ziv, Gal  (supervisor)orcid 
Conferred Date: 2021-02-23
Copyright Date: 2020-07
Thesis Restriction Date until: 2022-02-23
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Related DOI: 10.1007/s00122-021-03804-3
Related Research Outputs:

Grain size (GS) and grain weight (GW) are two key components of cereal yield that have been the subject of extensive research. Several candidateGS and GW genes are associated with quantitative trait loci (QTL) for grain weight. However, it is important to validate the precise roles of these genes. THOUSAND-GRAIN WEIGHT 6 (TGW6) is one such gene found in both rice (Oryza sativa) and wheat (Triticum aestivum). Inactive TGW6 alleles were reported to result in lower levels of the plant hormone, indole-3-acetic acid (IAA) and higher grain weight. The active allele was proposed to encode an IAA-glucose (IAA-Glc) hydrolase. Conversely, IAA biosynthesis mutants of rice (tsg1) and maize (de18) with reduced IAA levels have small or defective grains. Furthermore, most IAA in cereals is produced from tryptophan via tryptophan aminotransferase (TAR) and indole-3-pyruvate monooxygenase (YUCCA). The TGW6 work overlooked this source of IAA although TAR and YUCCA genes are also expressed in wheat grains. My study aimed to investigate whether TGW6 is the main source of IAA in developing wheat grains and whether inhibiting IAA production can increase grain size. I examined the expression of all genes contributing to IAA production during grain fill and compared this with grain IAA content. I also investigated the availability of IAA-Glc in grains to act as a substrate for TaTGW6. Lastly, a pilot experiment investigated whether inhibition of IAA biosynthesis has a positive or negative effect on grain yield. Expression of TaTAR2-B3, TaYUC9-1 and TaYUC10 increased 7–52 fold from 5 to 15 days after anthesis (DAA) correlating with a 30-fold increase in grain IAA content over the same period. On the other hand, TaTGW6 expression was not detected in grains. This was confirmed using published RNA-sequencing data, which showed TaTGW6 and OsTGW6 are both expressed in the inflorescence. In addition, TGW6 in cereals are part of a large protein family; TaTGW6 has eight homologues with over 80% amino acid identity. Finally, inhibition of IAA biosynthesis and IAA action had a negative effect on spike yield, but this was primarily due to increased grain abortion rather than an effect on grain size. My results show that TaTGW6 is unlikely to have any effect on the IAA content of grains or on grain size. On the other hand, I demonstrate that IAA is likely to have a positive effect on grain yield and primarily is produced from TAR/YUCCA pathway in developing wheat grains.

Publication Type: Thesis Doctoral
Fields of Research (FoR) 2020: 310803 Plant cell and molecular biology
300404 Crop and pasture biochemistry and physiology
300406 Crop and pasture improvement (incl. selection and breeding)
Socio-Economic Objective (SEO) 2020: 260312 Wheat
190101 Climate change adaptation measures (excl. ecosystem)
280102 Expanding knowledge in the biological sciences
HERDC Category Description: T2 Thesis - Doctorate by Research
Description: Please contact if you require access to this thesis for the purpose of research or study.
Appears in Collections:School of Environmental and Rural Science
School of Science and Technology
Thesis Doctoral

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