Abstract
Grain filling affects grain weight and quality and is among the most critical factors in determining the yield and quality of cereal crops. Though hybrids have larger panicles and numerous spikelets with a larger sink capacity than conventional varieties, data on the grain filling commonalities and differences between foxtail millet varieties with different panicle types remain sparse. In this study, we found that "Zhang Gu 13" (ZG, large panicle) exhibits a significantly higher panicle weight than "Yu Gu 18" (YG, conventional panicle) at the early stage of grain filling, but the weight of YG increased rapidly and gradually overtook ZG during the middle stages. A temporal expression pattern analysis demonstrated that the genes involved in photosynthesis, metabolic pathways, and phenylpropanoid biosynthesis were downregulated, while those related to peroxisome function, purine metabolism, and zeatin biosynthesis were upregulated during grain filling in both varieties. A total of 6,832 differentially expressed genes (DEGs) were identified in both varieties, with the majority identified at the early and late stages. A Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis further revealed that the upregulated DEGs in YG were associated with gibberellin (GA) biosynthesis, ATP-binding cassette (ABC) transporters, and plant hormone signal transduction. Photosynthesis-related DEGs, such as photosystem and antenna proteins, were significantly upregulated in ZG. This study provides preliminary insights into the differences in gene expression and molecular mechanisms of grain filling between ZG and YG in the North China summer-sowing region.