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Abstract

Leaf development involves the concerted action of various hormone signalling pathways and transcription factor networks. Some of the identified key transcriptional regulators include AINTEGUMENTA, JAGGED, BLADE ON PETIOLE, TCPs and GROWTH REGULATING FACTORS (GRFs). Here, we present insights in the role of miR396, a microRNA that regulates seven transcription factors of the plant specific GRF family. Transgenic plants with high miR396 levels have smaller leaves with fewer cells. Microarray analysis of 35S: miR396 plants revealed that this is likely a consequence of reduced mitotic activity. Nevertheless, leaf size was partially maintained by a compensating increase in cell size. We also performed a detailed analysis of the regulation of GRF2 by miR396. To do this, we prepared several reporters where we fused the β-glucoronidase reporter to the GRF2 gene. The motif recognized by miR396 was mutagenized to make a GRF2 reporter version either insensitive or hypersensitive to the miRNA. The results obtained from this analysis indicate that miR396 regulates the spatio-temporal pattern of GRF expression during leaf development. The participation of miR396 during Arabidopsis development will be discussed.