RNA interference and nucleolar dominance establishment in Arabidopsis suecica

Doutoramento em Biologia - Instituto Superior de AgronomiaThe discovery of small RNAs has added a new level to our understanding of gene regulation mechanisms. Small interfering RNAs (siRNAs) are involved in the establishment of repressive epigenetic marks in a variety of organisms by guiding RNA induced silencing complexes to homologous DNA sequences. Could the endogenous siRNA heterochromatic pathway be linked to the establishment of nucleolar dominance? The latter is a large scale manifestation of directed epigenetic gene silencing, resulting in the transcriptional inactivation of the entire rRNA gene cluster from one parent in a hybrid species. Inactivation of rRNA genes is linked to the establishment of heterochromatic marks, both at the DNA and histone levels, in the promoter region. We were able to identify 24nt siRNAs homologous to the rRNA gene promoter in Arabidopsis sp., whose biogenesis is dependent on nuclear RNA polymerase IV and other known proteins of the endogenous siRNA pathway in Arabidopsis. RNAi mediated knockdown of genes in this pathway in the natural allopolyploid hybrid A. suecica (A. thaliana x A. arenosa) disrupted nucleolar dominance, causing the production of rRNA transcripts from the underdominant A. thaliana rDNA genes. This observation implicates nuclear siRNAs in the establishment of nucleolar dominance in A. suecica