Expression Pattern of FT/TFL1 and miR156-Targeted SPL Genes Associated with Developmental Stages in Dendrobium...

Time to flower, a process either referring to juvenile-adult phase change or vegetative-reproductive transition, is strictly controlled by an intricate regulatory network involving at least both FT/TFL1 and the micro RNA (miR)156-regulated SPL family members. Despite substantial progresses recently achieved in Arabidopsis and other plant species, information regarding the involvement of these genes during orchid development and flowering competence is still limited. Dendrobium catenatum, a popular orchid species, exhibits a juvenile phase of at least three years. Here, through whole-genome mining and whole-family expression profiling, we analyzed the homologous genes of FT/TFL1, miR156, and SPL with special reference to the developmental stages. The FT/TFL1 family contains nine members; among them, DcHd3b transcribes abundantly in young and juvenile tissues but not in adult, contrasting with the low levels of others. We also found that mature miR156, encoded by a single locus, accumulated in large quantity in protocorms and declined by seedling development, coincident with an increase in transcripts of three of its targeted SPL members, namely DcSPL14, DcSPL7, and DcSPL18. Moreover, among the seven predicted miR156-targeted SPLs, only DcSPL3 was significantly expressed in adult plants and was associated with plant maturation. Our results might suggest that the juvenile phase change or maturation in this orchid plant likely involves both the repressive action of a TFL1-like pathway and the promotive effect from an SPL3-mediated mechanism.