The effect of auxin on wheat (Triticum aestivum L.) grain size is contentious. Additionally, the contributions to the IAA pool from de novo synthesis versus hydrolysis of IAA-glucose are unclear. Here, we describe the first comprehensive study of tryptophan aminotransferase and indole-3-pyruvate mono-oxygenase expression from 5 to 20 days after anthesis. A comparison of expression data with measurements of endogenous IAA via combined liquid chromatography–tandem mass spectrometry using heavy isotope labelled internal standards indicates that TaTAR2-B3, TaYUC9-A1, TaYUC9-B, TaYUC9-D1, TaYUC10-A and TaYUC10-D are primarily responsible for IAA production in developing grains. Furthermore, these genes are expressed specifically in developing grains, like those found in rice (Oryza sativa L.) and maize (Zea mays L.). Our results cast doubt on the proposed role of THOUSAND-GRAIN WEIGHT gene, TaTGW6, in promoting larger grain size via negative effects on grain IAA content. Work on this gene overlooked the contribution of IAA biosynthesis from tryptophan. Although IAA synthesis occurs primarily in the endosperm, we show the TaYUC9-1 group is also strongly expressed in the embryo. Within the endosperm, TaYUC9-1 expression is highest in aleurone and transfer cells, suggesting that IAA has a key role in differentiation of these tissues as has been proposed for other cereals.

生长素对小麦（Triticum aestivum L.）晶粒大小的影响是有争议的。此外，不清楚从头合成对IAA葡萄糖水解对IAA池的贡献。在这里，我们描述了花后5到20天对色氨酸氨基转移酶和吲哚-3-丙酮酸单加氧酶表达的首次全面研究。表达数据与使用重同位素标记内标的液相色谱-串联质谱联用测定内源IAA的比较表明，TaTAR2-B3，TaYUC9-A1，TaYUC9-B，TaYUC9-D1，TaYUC10-A和TaYUC10-D主要负责发展谷物的IAA生产。此外，这些基因在发育中的谷粒中特异性表达，就像在水稻（Oryza sativa L.）和玉米（Zea mays L.）中发现的那样。我们的研究结果对所提出的作用无疑投下THOUSAND -粒重基因，TaTGW6，在通过对粮食IAA含量的负面影响较大的促进晶粒尺寸。该基因的研究忽略了色氨酸对IAA生物合成的贡献。尽管IAA合成主要发生在胚乳中，但我们显示TaYUC9-1基团在胚胎中也强烈表达。在胚乳内，TaYUC9-1 蛋白的表达在糊粉和转移细胞中是最高的，这表明IAA在这些组织的分化中起着关键作用，正如其他谷物所建议的那样。