LAUSR

The flower of Zingiber zerumbet is characterized by a distinctive labellum, a highly modified floral organ believed to be formed by the fusion of several infertile members of the androecial whorl (staminodes). Across the Zingiberaceae, the number of staminodes involved in labellum formation varies from two to four, and these are reflected in the number of lobes that comprise the mature labellum. Research on the flower development in Zingiberaceae has been limited to species with either no labellum lobes or species displaying a bilobed labellum. Zingiber zerumbet is a representative of the genus with a three-lobed labellum, and its flower development remains poorly understood at both morphological and molecular levels. This study aims to give a comprehensive description of its flower development and to identify potential genes related to flower development using morphological and genetic characterization. Our results show that floral organ initiation is sequential with the sepal whorl initiating first, followed by petal and inner androecium together, followed by outer androecium, and finally the initiation of the inferior gynoecium. The three-lobed labellum comprises four androecial members: Two abaxial inner androecial members fuse to form the single central lobe, and two adaxial outer androecial members individually form the two lateral lobes of the labellum. Two developmental stages (floral primordium and organ-differentiated flowers) were selected for transcriptome sequencing. Two-thousand and seventy-five transcription factors were identified. Seven boundary genes and seven organ-specific genes were also discovered. Our study provides fundamental information for further studies on the molecular mechanisms of flower development and evolution across the Zingiberaceae.