The INDEHISCENT protein regulates unequal cell divisions in Arabidopsis fruit

INDEHISCENT (IND) is one of the major factors of a transcriptional network regulating fruit dehiscence in Arabidopsis thaliana. However, partially owing to the lack of knowledge on the morphogenic process at the junction between the valve margin and the replum, the cellular processes regulated by IND have not been elucidated. Here we report the identification of a zone of seven layers of cells relevant to silique dehiscence, and the isolation and characterization of a transposon-enhancer-trap-generated null allele of IND, ind-6. Light microscopy analysis revealed that the beta-glucuronidase from the enhancer trap was expressed in a seven-layer zone, encompassing the valve margin and the replum border. Electron and light microscopy analyses also revealed that unequal cell divisions actively occurred at stage 15 in the seven-layer zone in wild type (WT), which apparently produced the distinct cell types in the WT seven-layer zone. In contrast, siliques of ind-6 at stage 15 did not exhibit such cell divisions but fewer cells and defective cytokinesis, hence lacking the distinct cell types in the seven-layer zone. These results demonstrate a cellular mechanism for establishing the distinct cell types and a role for IND in regulating the unequal cell divisions in the seven-layer zone.