A conserved microRNA module exerts homeotic control over Petunia hybrida and Antirrhinum majus floral organ identity

It is commonly thought that deep phylogenetic conservation of plant microRNAs ( miRNAs) and their targets(1,2) indicates conserved regulatory functions. We show that the blind ( bl) mutant of Petunia hybrida(3) and the fistulata ( fis) mutant of Antirrhinum majus(4,5), which have similar homeotic phenotypes, are recessive alleles of two homologous miRNA- encoding genes. The BL and FIS genes control the spatial restriction of homeotic class C genes(6,7) to the inner floral whorls, but their ubiquitous early floral expression patterns are in contradiction with a potential role in patterning C gene expression. We provide genetic evidence for the unexpected function of the MIRFIS and MIRBL genes in the center of the flower and propose a dynamic mechanism underlying their regulatory role. Notably, Arabidopsis thaliana, a more distantly related species, also contains this miRNA module but does not seem to use it to confine early C gene expression to the center of the flower.