Heading date 3a (Hd3a) is an important flowering regulator of short-day plants, and plays a role in several developmental processes. The oil palm is commercially grown for the edible oil derived from its fruit. Flowering and fruit development are key factors for successful production, contributing to productivity of the oil palm fruit. Because little is known about the gene organization of Hd3a in the oil palm, the present study aimed at isolating the Hd3a and its regulatory region. Furthermore, alternatively spliced transcripts were cloned, and their expression in different tissues was also investigated. The structure of the oil palm Hd3a (EgHd3a-like) gene and its promoter were established based on the isolation of EgHd3a-like cDNA and genomic DNA. The promoter analysis revealed that it contains two key regulatory elements, CCAAT boxes and an ARR1 motif, which are the binding sites of Hd3a inducers. Other cis-elements corresponding to flowering and organ development were also represented. Expression of the transcript variants was investigated by RT-PCR in the anther, pistil, mesocarp and leaf. EgHd3a-like was expressed in all tissues tested, which supports its multifaceted roles in several developmental processes. The variants were found in all tested tissue types but at different levels, showing some level of tissuespecificity by variant. Taken together, these results indicate that EgHd3a-like is regulated under various conditions and that transcript variants might play an important role in gene function and regulation.
