THE miR396 REGULATORY NETWORK IN PLANTS: BIOLOGICAL FUNCTION AND EVOLUTIONARY DIVERGENCE BETWEEN SPECIES

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

Pto Madryn

Simposio; XLVI Reunión Anual de la Sociedad Argentina de Investigaciones en Bioquímica y Biología Molecular; 2010

Leaf primordia are initiated by recruiting cells from the peripheral zone of the shoot apical meristem. Extensive mitosis proceeds until cells begin to enlarge. This process is regulated by the concerted action of various transcription factor networks, among them the GROWTH REGULATING FACTORS (GRFs). We present insights into the role of miR396 in Arabidopsis leaf development. Mir396 regulates seven transcription factors of the GRF family. Overexpression of this miRNA lead to downregulation of GRFs and reduced leaf cell number. Conversely, high levels of GRF2 activity increased cell proliferation in leaves. Using reporter constructs, we determined that miR396 is essential to establish a dynamic spatio-temporal pattern of GRF2 expression that coincides with the activity of cell proliferation. Analysis of miR396 and its targets in various plants species revealed two different types of divergence of this conserved regulatory module. First, particular miR396 variants are expressed only in monocots. Expression of these versions in Arabidopsis indicated that they are stronger repressors than the Arabidopsis counterparts. Second, a search for novel miR396 targets revealed that a basic-helix-loop-helix transcription factor is regulated only in a group of Brassicales. The importance miR396-mediated repression of this bHLH for normal Arabidopsis development will be discussed.