Organ-Specific Gene Expression Reveals the Role of the 396 Module in Flower Development of the Orchid Plant .

Orchids are some of the most popular ornamental plants worldwide. Orchid floral morphology has increasingly attracted horticultural and commercial attention. Although multiple genes have been shown to be involved in the formation of the orchid flower, the underlying multi-level regulatory networks are largely unknown. In this study, we analyzed the ontogeny of flower development in , a traditional orchid in the tropical and subtropical regions of Asia, by performing deep sequencing of the transcriptome of individual flower organs to discover organ-specific genes potentially involved in their growth. We identified 3,017 differentially-expressed genes (DEGs) during the development of various flower organs, and observed over-representation of () specific to flower column (gynostemium). Eleven () from our transcriptome data clustered into five phylogenetic subgroups. Ten of these shared a region complementary to microRNA396 (-miR396), and degradome sequencing confirmed the cleavage of transcripts derived from seven . We cloned miR396 and used a protoplast-based transient expression system to overexpress it in protoplasts. We observed a significant decrease in the transcripts of several in flowers and leaves, indicating a potential role for miR396-GRF module in organ development through the cleavage of distinct . Temporal and spatial expression analysis indicated that most transcripts accumulated in flower buds and column tissues, where -miR396 expression was the lowest. Expression dynamics in wild type and floral-defective mutants further confirmed a strong correlation between -miR396, , and flower organ development and column specification. Moreover, overexpression of -miR396 in resulted in curved pistils and reduced fertility, implying that the conserved role of -miR396 in floral development. These results provide tools to better understand the biological roles of in orchid development, and open new avenues for the diversification of orchid floral patterns.