Identification and characterization of genes regulating flowering time in apricots

Apricot blossoms and seed kernels are valuable medicine and biodiesel feedstock, respectively. Frequent frosts in early spring often result in reduction or complete loss of apricot blossoms, fruits and seeds. Therefore, breeding late flowering varieties of the apricot is one of the important strategies to avoid frost damage. However, the mechanism regulating flowering time remains largely unknown in this species. Here, the transcriptomes of the apricot cultivars Weixuan No.1 (Prunus armeniaca L., late flowering) and Shanxing (Prunus sibirica L., early flowering) were analyzed to identify the genes regulating flowering time. The pairwise comparison identified 4900 genes with differential expression between cultivars. From these, 36 genes were identified related to apricot flowering time, including FLOWERING LOCUS T (PaFT, PARG03266), FOLLOWER LOCUS D (PaFD, PARG27379), and PROTEIN ARGININE METHYLTRANSFERASE 10 (PaPAMT10, PARG28000), their ectopic expression in Arabidopsis promoted early flowering. Additionally, one MADS-box transcription factor family member, PaAGL15-like (PARG25423), was retrieved from the differentially expressed transcription factors between Shanxing and Weixuan No.1. Subsequent experiments showed that the ectopic expression of PaAGL15-like in Arabidopsis promoted early flowering. In these transgenic plants, eight genes, including AtFT and miR156-targeted AtSPL3, were significantly enriched during the transition from the vegetative to the reproductive phase. Yeast one-hybrid and transient dual luciferase assays further showed that PaAGL15-like activated AtFT but repressed AtmiR156b by directly binding to their promoter sequences. Finally, our study proposes four genes PaFT, PaFD, PaPAMT10, and PaAGL15-like as potential targets for fine-tuning flowering time to improve apricot blooms and seed kernel yield.