The GRF–GIF duo and AINTEGUMENTA act cooperatively for the meristematic competence of lateral organs in Arabidopsis

Above-ground lateral organs, such as leaves and flowers, should grow to an optimal size and develop particular structures, which are primarily determined by the meristematic activities of their primordia. The GROWTH-REGULATING FACTOR (GRF)–GRF-INTERACTING FACTOR (GRF–GIF) transcriptional complex and the AINTEGUMENTA (ANT) transcription factor play key roles in the establishment of the meristematic competence of lateral organ primordia with highly overlapping expression patterns, and thus functional relationships between them have long been speculated. In this study, we constructed the ant gif1 gif2 gif3 quadruple mutant, which produced much smaller and narrower leaves, sepals, and petals with far fewer cells compared with its parental lines. Furthermore, the mutant gynoecium completely lacked carpel margin meristems, resulting in neither carpel fusion nor ovule formation, indicative of a profound level of genetic interaction between ANT and GIF genes. Similarly, construction and analysis of ant 35S::MIR396b and ant grf1 grf3 grf4 grf5 quintuple mutants revealed genetic interaction between ANT and GRF genes. We also found interdependence of GRF–GIF and ANT expression and the regulatory convergence of GRF–GIF and ANT signaling pathways on cell cycle regulator genes, and that GRF–GIF action was dependent on functional ANT, providing the molecular basis for the genetic interaction.