Control of leaf growth in Arabidopsis thaliana by microRNA miR396

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

La Plata

Congreso; XXVIII Reunión Anual de Fisiología Vegetal.; 2010

Leaf primordia are initiated by recruiting cells from the peripheral zone of the shoot apical meristem. Extensive cell proliferation occurs during leaf organogenesis, extending even days after primordia initiation. Once cells cease to divide, they begin to enlarge and cell growth becomes the driving force regulating organ size. This process is regulated by the concerted action of various transcription factor networks, such as AINTEGUMENTA, JAGGED, BLADE ON PETIOLE, TCPs and GROWTH REGULATING FACTORS (GRFs). Here, we present insights into the role during leaf development of miR396, a microRNA that regulates seven transcription factors of the plant specific GRF family. High levels of miR396 lead to downregulation of mitosis-specific genes, which in turn dramatically reduced leaf cell number. Nevertheless, leaf size was partially maintained by a compensating increase in cell size. Conversely, elevated GRF2 activity increased cell proliferation in leaves. Using reporter constructs, we found a dynamic spatio-temporal pattern of GRF2 expression that coincided with the activity of cell proliferation during leaf development. We further determined that miR396 was essential to establish this dynamic pattern of expression. Additionally, we observed that miR396 regulates the size and cell proliferation of the shoot apical meristem itself. Finally, the interaction of miR396 and GRFs with other transcription factors involved in leaf development will be discussed.