Transcriptomic Analysis of the Maize Mutant TC19 Identifies Genes Regulating the Development of Grain Size Through the IAA and BR Pathways

Abstract Backgrounds: Grain size is a key factor in crop yield that gradually develops after pollination. However, few studies have reported gene expression patterns in maize grain development using mutants. To investigate the developmental mechanisms of grain size, we analyzed a large-grain mutant, named TC19, at the morphological and transcriptome level at five stages corresponding to days after pollination (DAP).Results: After maturation, the grain length, width, and thickness in TC19 were greater than that in Chang 7-2 (control) and increased by 3.57%, 8.80%, and 3.88%, respectively. Further analysis showed that grain width in TC19 was lower than in Chang 7-2 at 7, 14, and 21 DAP, but greater than that in Chang 7-2 at 28 and 35 DAP, indicating that 21 to 28 DAP was the critical stage for kernel width development. For all five stages, the concentrations of indole-3-acetic acid and brassinosteroids were significantly higher in TC19 than in Chang 7-2. Gibberellin was higher at 7, 14, and 21 DAP, and cytokinin was higher at 21 and 35 DAP, in TC19 than in Chang 7-2. Through transcriptome analysis at 14, 21, and 28 DAP, we identified 2987, 2647, and 3209 differentially expressed genes (DEGs) between TC19 and Chang 7-2. Gene Ontology analysis indicated that most of the grain size–related genes corresponded to three aspects, including cell components, molecular functions, and biological processes. The Kyoto Encyclopedia of Genes and Genomes pathway analysis showed that 77 DEGs were enriched in the plant hormone signal transduction pathway. We further analyzed several highly expressed candidate genes, including AO2, ARF3, and IAA15, which are involved in the synthesis of IAA; and DWF4 and XTH, which are involved in the synthesis of BR.Conclusions: Our results elucidated the mechanisms of grain size development at the grain-filling stage and have potential application in maize breeding.