Conserved functional control, but distinct regulation, of cell proliferation in rice and Arabidopsis leaves revealed by comparative analysis of GRF-INTERACTING FACTOR 1 orthologs

Regulation of cell proliferation is crucial for establishing the shape of plant leaves. We have identified MAKIBA3 (MKB3), a loss-of-function mutant of which exhibits a narrowed- and rolled-leaf phenotype in rice. MKB3 was found to be an ortholog of Arabidopsis ANGUSTIFOLIA3 (AN3), which positively regulates cell proliferation. The reduced leaf size of mkb3 plants with enlarged cells and the increased size of MKB3-overexpressing leaves with normal-sized cells indicate that MKB3 is a positive regulator of leaf proliferation and that mkb3 mutation triggers a compensation syndrome, as does Arabidopsis an3. Expression analysis revealed that MKB3 is predominantly expressed on the epidermis of leaf primordia, which is different from the location of AN3. A protein movement assay demonstrated that MKB3 moves from an MKB3-expressing domain to a non-expressing domain, which is required for normal leaf development. Our results suggest that rice MKB3 and Arabidopsis AN3 have conserved functions and effects on leaf development. However, the expression pattern of MKB3 and direction of protein movement are different between rice and Arabidopsis, which might reflect differences in leaf primordia development in these two species.