Hybrid larch is an excellent afforestation species in northern China. The instability of seed yield is an urgent problem to be solved. The biological characteristics related to seed setting in larch are different from those in angiosperms and other gymnosperms. Studying the developmental mechanism of the larch sporophyll can deepen our understanding of conifer reproductive development and help to ensure an adequate supply of seeds in the seed orchard. The results showed that the formation of microstrobilus primordia in hybrid larch could be observed in anatomical sections collected in the middle of July. The contents of endogenous gibberellin 3 (GA3) and abscisic acid (ABA) were higher and the contents of GA4, GA7, jasmonic acid and salicylic acid were lower in multiseeded larch. Transcriptome analysis showed that transcription factors were significantly enriched in the AP2 family. There were 23 differentially expressed genes in the buds of the multiseeded and less-seeded types, and the expression of most of these genes was higher in the buds than in the needles. We conclude that mid-July is the early stage of reproductive organ development in hybrid larch and is suitable for the study of reproductive development. GA3 and ABA may be helpful for improving seed setting in larch, and 23 AP2/EREBP family genes are involved in the regulation of reproductive development in larch.

AP2/ERF is an important transcription factor family involved in physiological processes such as plant development and hormone signaling. In this study, based on the available transcriptome data of hybrid larch during floral induction, 13 DREB genes belonging to the AP2/EREBP family with complete CDS regions were identified through alignment using the NCBI website. We conducted a bioinformatics analysis on the gene sequences, examining their tissue specificity, response to hormone treatment, and response to environmental factors. The DREB genes in hybrid larch (Larix kaempferi × Larix olgensis) showed tissue-specific expression, with DREB7, DREB8, DREB10, DREB12, and DREB13 exhibiting higher expression levels in nascent buds and higher expression in female cones compared to male cones. They also showed high expression during signal convergence and floral induction, and were highly expressed in materials with good fertility, suggesting their positive role in the cone-setting process of hybrid larch. Additionally, 13 DREB genes were all induced by abscisic acid (ABA), gibberellin 3 (GA₃), and indoleacetic acid (IAA), with the most pronounced expression changes observed after ABA treatment, indicating that these genes might be mainly regulated by ABA. In response to temperature and photoperiod treatments, DREB7, DREB8, DREB10, DREB12, and DREB13 showed significant responses, with increased expression levels induced by low temperature, while no clear pattern was observed after long or short-day treatments. These results of the study provide a reference for understanding the function of the DREB gene family in hybrid larch, offer a theoretical basis for inducing floral bud differentiation in hybrid larch, and contribute to a better understanding of the molecular mechanisms underlying cone-setting in hybrid larch.