The Role of the REPLUMLESS Homeodomain Protein in Patterning the Arabidopsis Fruit

The outside of the Arabidopsis thaliana fruit consists of three principal tissues: the valves or seedpod walls, the replum or central ridge between the valves, and the valve margins where the valves separate from the replum to disperse the seeds. Previous studies have shown that valve margin formation is specified by the SHATTERPROOF MADS-box transcription factors [1Liljegren S.J. Ditta G.S. Eshed Y. Savidge B. Bowman J.L. Yanofsky M.F. SHATTERPROOF MADS-box genes control seed dispersal in Arabidopsis.Nature. 2000; 404: 766-770Crossref PubMed Scopus (627) Google Scholar] and that valve development is controlled by the FRUITFULL MADS-box transcription factor [2Gu Q. Ferrándiz C. Yanofsky M.F. Martienssen R. The FRUITFULL MADS-box gene mediates cell differentiation during Arabidopsis fruit development.Development. 1998; 125: 1509-1517PubMed Google Scholar]. FRUITFULL negatively regulates SHATTERPROOF to prevent the valves from adopting a valve margin cell fate [3Ferrándiz C. Liljegren S.J. Yanofsky M.F. Negative regulation of the SHATTERPROOF genes by FRUITFULL during Arabidopsis fruit development.Science. 2000; 289: 436-438Crossref PubMed Scopus (316) Google Scholar]. Here we identify a gene called REPLUMLESS that is required for replum development. REPLUMLESS encodes a homeodomain protein that prevents replum cells from adopting a valve margin cell fate by negatively regulating expression of the SHATTERPROOF genes. Both REPLUMLESS and FRUITFULL are required to limit SHATTERPROOF expression to a narrow stripe of cells so that the valve margin differentiates precisely at the valve/replum boundary.