The basic leucine-zipper transcription factor DlbZIP36 is involved in regulating flowering in longan

Longan (Dimocarpus longan Lour.) is a well-known subtropical fruit crop. However, the narrow harvest window seriously affects its economic benefits. Flowering time is a key factor that determines the ripening time of longan. Previous studies have demonstrated that ethephon and paclobutrazol treatment can regulate the flowering time of 'Sijimi' longan, and further transcriptomic analysis found that the basic leucine zipper (bZIP) transcription factor family may play a key role in this regulation process. Here, to reveal the functions of bZIP proteins in 'Sijimi' longan, we cloned 39 DlbZIP genes identified by a genome wide domain analysis, which were designated as DlbZIP1-39. Analysis of the temporal and spatial expression patterns of these genes showed that DlbZIP36 had higher expression in petioles, and the expression was significantly enhanced by ethephon and paclobutrazol treatments. Subcellular localization analysis showed that DlbZIP36 is located in the nucleus. Finally, ectopic overexpression of DlbZIP36 in Arabidopsis resulted in earlier flowering under long day conditions, and led to higher expression of Arabidopsis FLOWERING LOCUS T (AtFT) and FRUITFULL (AtFUL) while lower expression of Arabidopsis FLOWERING LOCUS C (AtFLC) than the wild type. In addition, overexpression of DlbZIP36 in tobacco also resulted in early flowering. These results suggest that DlbZIP36 may enhance the flowering of 'Sijimi' longan under ethephon and paclobutrazol treatment, providing an important theoretical basis for the perinatal regulation and breeding of longan in the future.