Format: ORAL

Yesenia Madrigal [1], MichaelScanlon [2], Marian Bemer [3], Juan F.Alzate [4], and NataliaPabn-Mora [1].

[1] Instituto de Biología, Universidad de Antioquia, Medellín, Colombia, 050010, Cl. 67 #53-108 [2] School of Integrative Plant Science, Cornell University, Ithaca, US. 236 Tower Rd, Plant Science building. 14850 [3] Plant Developmental Systems, Wageningen University and Research, Droevendaalsesteeg 1, 6708 PB, Wageningen, the Netherlands [4] Centro Nacional de Secuenciación Genómica, SIU, Universidad de Antioquia, Medellín, Colombia, 050010. Cl. 62 #52-59

Flowering in angiosperms occurs when vegetative meristems (VM) that form leaves become inflorescence meristems (IM) that form bracts and flowers. This process has been comprehensively studied in monocots, such as Oryza sativa, where the genetic regulatory network (GRN) includes promoter genes such as FT, COL and FUL that activate floral meristem identity genes. There are also repressors involved in the maintenance of vegetative phases that include TFL1 and AGL24/SVP, in addition to FLC and VRN2 that are important in response to cold. In contrast, little is known about how flowering is genetically controlled in neotropical orchids with different habits that colonize different micro-niches and respond to subtle environmental changes. We performed an exhaustive analysis of the morpho-anatomical and transcriptomic changes from VM to IM in three orchids: Epidendrum fimbriatum (miniature terrestrial), Cattleya trianae (epiphytic with storage organs), and Elleanthus aurantiacus (a big size terrestrial). Our RNAseq results show a higher proportion of differentially expressed genes (DEGs) involved in flowering in terrestrial species compared to epiphytic taxa. Conversely, a greater number of genes related to the metabolism of sugars and lipids was found in the epiphytic species. The most important flowering transcription factors within the DEGs include the promoters FT2A, FD2A, FUL1B/1A, SOC1La, LFY and the repressors COL4A/4B, SVP2A, GHD7, AP2 and TFL1. We validated our results using spatiotemporal expression by ISH and by protein-protein interaction using Y2H. We found important differences between the flowering GRN in orchids and model crops in the Poaceae: 1) high duplication rates for flower integrators in orchids but a low percentage of transcriptionally active homologs; 2) the retention of canonical flowering integrators, at the expense of low expression, loss of key protein interactions, and possibly pseudogenization of some homologs; and 3) changes in transcriptomic profiles in different orchids according to their morphological adaptations and habits.