Systematic Assessment of the Positive Role of Arabidopsis thaliana GROWTH-REGULATING FACTORs in Regulation of Cell Proliferation During Leaf Growth

Leaf growth and development are primarily driven by cell proliferation and expansion. Among a number of genes involved in the regulation of cell proliferation, the GROWTH-REGULATING FACTOR (GRF) transcription factors have been established to act as positive regulators of cell proliferation and leaf growth in angiosperms. While the Arabidopsis thaliana GRF family comprises nine members, not all members of the family have been experimentally confirmed for the positive role, not only due to no or only slight changes in leaf size of corresponding single mutants, but also due to unavailability of multiple mutants to overcome the obstacle. Furthermore, some discrepancies and confusion in their roles have been disclosed in the literature. Here, we systemically prepared a series of such multiple mutants and confirmed that all GRF members, except for GRF8, acted as positive regulators of cell proliferation and leaf growth. We also systematically examined the spatio-temporal distribution patterns of all nine GRF proteins in the leaf organ, and found that their distribution patterns were highly reminiscent of the behavior of the cell cycle arrest front. We therefore propose that GRFs play an important role in shaping the arrest front and growth patterns of leaves.