Grain number and weight are two key factors that influence cereal yield. Both are regulated by hormone signalling in developing grains. The hormone auxin, or indole-3-acetic acid (IAA) is particularly important for grain filling. Most publications have shown a positive correlation between IAA and grain weight in cereals. However, two reports on the THOUSAND GRAIN WEIGHT 6 (TGW6) genes in rice and wheat have shown a negative correlation. TGW6 is reported to encode IAA-glucose hydrolase. Both papers have published that inactive TGW6 alleles result in lower IAA levels in developing grains and higher grain weight. The TGW6 work has however overlooked the major source of IAA in grains. The main pathway of IAA production starts from tryptophan (Trp) which is converted to IAA using the products of two genes; TAR encoding Trp aminotransferase and YUCCA encoding indole pyruvate monooxygenase. The IAA-glucose that is required as a substrate for IAA-glucose hydrolase must be produced from IAA via the activity of a UDP-glucose transferase (IAGLU). In this work, we have shown that the expression of specific TAR and YUCCA genes increases during grain development from five to fifteen days after pollination (DAP) in wheat, coinciding with the major increase in grain weight. This suggests that the TAR/YUCCA pathway is actively producing IAA during this time. On the other hand, we failed to confirm expression of TGW6 in wheat grains from five to twenty DAP. Furthermore, we have shown that there are seven other genes in wheat with at least 80% amino acid identity to TGW6 and a further 20 TGW6-like genes with at least 52% amino acid identity. It is thus difficult to understand how one inactive TGW6 allele as reported in the TGW6 papers could have a major effect on either IAA content or grain weight. In addition, neither paper has investigated whether there is a pool of IAA-glucose available as a substrate for IAA-glucose hydrolase. We investigated the expression of wheat coorthologues of rice and maize IAGLU genes but were unable to detect during early grain development. This study questions whether TGW6 actually affects grain weight by altering auxin metabolism in wheat.