[Plant hormone signaling is involved in regulating flower bud size of daylily].

To explore the role and metabolic differences of plant hormones in regulating the flower bud size of daylily, we collected the flower buds from two daylily varieties 'Datong Huanghua' and 'Dongbei Huanghua' at the young bud, green, yellowing, and yellow stages for transcriptome sequencing. The differentially expressed genes (DEGs) were screened, and the exogenous plant hormone spraying experiments were conducted. A total of 199 DEGs related to the biosynthesis and metabolism of plant hormones was screened out at different flower development stages of 'Datong Huanghua' and 'Dongbei Huanghua'. These genes regulated the biosynthesis and metabolism of six plant hormones: abscisic acid, gibberellin, auxin, jasmonate, cytokinin, and ethylene. The DEGs associated with auxin were the most, which suggested that auxin played a role in regulating flower bud development. The auxin response factor (<i>ARF</i>) presented up-regulated expression at all the four stages of flower bud development, indicating that <i>ARF</i> played a positive regulatory role throughout the flower bud development of daylily. The experiments with exogenous spraying of six hormones further verified that indole-3-acetic acid (IAA) significantly promoted the growth and increased the nutrient content in the flower buds of 'Datong Huanghua', suggesting that IAA played a role in regulating flower bud development. Our results laid a theoretical foundation for probing into the regulatory mechanism of flower bud development of 'Datong Huanghua' and 'Dongbei Huanghua'.