Isolation and characterization of GI and FKF1 homologous genes in the subtropical fruit tree Dimocarpus longan

Abstract

Longan (Dimocarpus longan Lour.) is a subtropical fruit tree of significant economic importance. Flowering is a key event in longan and other fruit trees. In this study, GIGANTEA (GI) and FLAVIN-BINDING, KELCH REPEAT, F-BOX1 (FKF1) homologs were cloned from longan and named DlGI and DlFKF1, respectively. Translated sequences of DlGI and DlFKF1 revealed a high homology to GI and FKF1 sequences from other plants. DlGI and DlFKF1 transcript levels varied seasonally in the shoots and leaves during floral bud differentiation of longan. Expression levels of DlGI and DlFKF1 in the shoot tips increased and reached a peak in November which is the time of physiological differentiation of floral buds in longan. Ectopic overexpression of DlGI and DlFKF1 in Arabidopsis resulted in early-flowering phenotypes and adventitious root formation under LD conditions. The expression levels of YUCCA 9 and PIN-FORMED 2 were found to be elevated in DlGI-overexpressing and DlFKF1-overexpressing Arabidopsis plants under LD conditions. These results suggest that both DlGI and DlFKF1 are flowering promoters and they might be involved in the regulation of physiological differentiation of floral buds, inducing floral initiation by affecting endogenous auxin synthesis and transport in longan. Our results will provide more insight into flowering regulation in longan and woody plants.