Expression data from rGRF3, 35S:GIF1 and rGRF3x35S:GIF1 plants

The Growth Regulating Factors (GRFs) are plant specific transcription factors. They form complexes with GRF Interacting Factors (GIFs), a small family of transcriptional co-activators. In Arabidopsis thaliana, seven out of the nine GRFs are regulated by microRNA miR396. A detailed analysis of GRF3 revealed that a modified transgene, insensitive to the regulation of miR396, causes a strong increase in the number of cells in leaves, while an additional increase of GIF1 expression further enhances the number of cells synergistically. Genome-wide transcript profiling revealed that simultaneous increase of GRF3 and GIF1 levels causes additional effects in gene expression compared to either of the transgenes alone. We observed that GIF1 interacts in vivo with GRF3, as well as chromatin remodeling complexes, providing a mechanistic explanation for the additional activities of a GRF3-GIF1 complex. Interestingly, we found that the GRF system also regulates leaf longevity. Genetic and molecular analysis revealed that the functions of GRFs in leaf size and senescence can be uncoupled, demonstrating that the GRFs control different stages of leaf development. The results provide new insights into the functions of a complex regulatory network composed of microRNAs, transcription factors, and co-transcription factors.

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Debernardi JM, Mecchia MA, Vercruyssen L, Smaczniak C, Kaufmann K, Inze D, Rodriguez RE, Palatnik JF