Functional Specialization of the Plant miR396 Regulatory Network through Distinct MicroRNA-Target Interactions

DEBERNARDI, JUAN MANUEL; RODRIGUEZ VIRASORO, RAMIRO ESTEBAN; MECCHIA, MARTIN; PALATNIK, JAVIER

PLOS GENETICS

PUBLIC LIBRARY SCIENCE

Año: 2012

1553-7390

MicroRNAs (miRNAs) are ,21 nt small RNAs that regulate gene expression in animals and plants. They can be grouped intofamilies comprising different genes encoding similar or identical mature miRNAs. Several miRNA families are deeplyconserved in plant lineages and regulate key aspects of plant development, hormone signaling, and stress response. Theancient miRNA miR396 regulates conserved targets belonging to the GROWTH-REGULATING FACTOR (GRF) family oftranscription factors, which are known to control cell proliferation in Arabidopsis leaves. In this work, we characterized theregulation of an additional target for miR396, the transcription factor bHLH74, that is necessary for Arabidopsis normaldevelopment. bHLH74 homologs with a miR396 target site could only be detected in the sister families Brassicaceae andCleomaceae. Still, bHLH74 repression by miR396 is required for margin and vein pattern formation of Arabidopsis leaves.MiR396 contributes to the spatio-temporal regulation of GRF and bHLH74 expression during leaf development. Furthermore,a survey of miR396 sequences in different species showed variations in the 59 portion of the miRNA, a region known to beimportant for miRNA activity. Analysis of different miR396 variants in Arabidopsis thaliana revealed that they have anenhanced activity toward GRF transcription factors. The interaction between the GRF target site and miR396 has a bulgebetween positions 7 and 8 of the miRNA. Our data indicate that such bulge modulates the strength of the miR396-mediatedrepression and that this modulation is essential to shape the precise spatio-temporal pattern of GRF2 expression. The resultsshow that ancient miRNAs can regulate conserved targets with varied efficiency in different species, and we further proposethat they could acquire new targets whose control might also be biologically relevant.