Postdoc Pennsylvania State University STATE COLLEGE, Pennsylvania
Body of Abstract: Regulation of floral gene expression is crucial for flower development1,2. Flower organ identity in Arabidopsis of other angiosperms is controlled by highly conserved homeotic genes of the MADS-box (an acronym of MCM1, AGAMOUS, DEFICIENS, and SRF) and the AP2 gene families3. However, the regulation of pre-mRNA splicing (hereafter RNA splicing) in flower development is largely unknown, including the proper splicing of known floral regulatory genes. Unusual exons shorter than average sizes (< 51 bp) called micro-exons are widely presented in plants and animals4, but lack proper binding motifs for known splicing factors. Micro exons are enriched in MIKC-type MADS-box genes and AP2 domain genes in plants, including floral homeotic ABCDE genes5. However, the regulators and mechanisms in micro-exon splicing in plants are still unknown. Here, we present that gene structures of ABC genes are highly conserved among major angiosperm lineages. Specifically, micro exons are generally present in ABC homologs and encode functional K domains in MADS-box genes and AP2 domains in AP2 family genes, suggesting that these micro exons might allow additional regulatory mechanisms. Moreover, we uncovered that micro exon is required for normal function of ABC genes in Arabidopsis. Importantly, we describe a novel regulator named FRB1 (Floral RNA Binding 1) that is required for normal floral organ development, including their number, identity, shape, and size. Further, an investigation of gene expression profiles in the frb1 mutant revealed abnormal skipping of key micro exons of ABC genes, indicating the importance of FRB1 in micro exon splicing of ABC genes. These results are strong evidence that FRB1 is a novel and crucial regulator of RNA splicing for normal flower development and that micro exon regulation might be conserved among angiosperms.