Regulatory Landscape of Small Intergenic Regions in a Compact Plant Genome

The carnivorous plant Utricularia gibba is a small specie of bladderwort of the Lentibulariaceae family that has one of the smallest known angiosperm genomes at 82 megabases, which is approximately half the size of Arabidopsis. This genome suffer a compaction that presumably was associated to loss of nonessential intra and inter-genomic sequences such as size reduction of intergenic regions but mantaining a similar number of genes for a plant, an interesting feature when its lineage had undergone three independent whole genome duplication events since its divergence with Solanaceae. Here we focus on understanding the functionality of  this small sequences after genome reduction process making the functional analysis of small intergenic regions in Utricularia gibba genome at the transcriptional level. We found that small intergenic  are functional and shows that this putative promoters direct expression in Arabidopsis in similar form to homologous regions but not identical because of differences between plant complexity. All promoter regions maintain Cis-regulatory motifs in comparison with Arabidopsis and some have compacted their regulatory elements to certain areas maintaining all the necessary elements to regulate expression. One small region contain a bidirectional promoter that regulate the expression in divergent genes. In Silico analysis of functional categories in divergent genes we find that this genes have particular functions such DNA metabolism. In conclusion we show an expression outlook at transcriptional level of a small intergenic regions of a plant genome that suffer a miniturization process with bioinformatic studies of motifs in this sequences and functional categorization.