THE FRUITFULL MADS-BOX GENE MEDIATES CELL-DIFFERENTIATION DURING ARABIDOPSIS FRUIT-DEVELOPMENT

Fruit morphogenesis is a process unique to flowering plants, and yet l ittle is known about its developmental control, Following fertilizatio n, fruits typically undergo a dramatic enlargement that is accompanied by differentiation of numerous distinct cell types. We have identifie d a mutation in Arabidopsis called fruitfull (ful-1), which abolishes elongation of the silique after fertilization. The ful-1 mutation is c aused by the insertion of a DsE transposable enhancer trap element int o the 5' untranslated leader of the AGL8 MADS-box gene. beta-glucuroni dase (GUS) reporter gene expression in the enhancer trap line is obser ved specifically in all cell layers of the valve tissue, but not in th e replum, the septum or the seeds, and faithfully mimics RNA in situ h ybridization data reported previously, The lack of coordinated growth of the fruit tissues leads to crowded seeds, a failure of dehiscence a nd, frequently, the premature rupture of the carpel valves, The primar y defect of ful-1 fruits is within the valves, whose cells fail to elo ngate and differentiate. Stomata, which are frequent along the epiderm is of wild-type valves, are completely eliminated in the ful mutant va lves. In addition to the effect on fruit development, ful cauline leav es are broader than those of wild type and show a reduction in the num ber of internal cell layers. These data suggest that AGL8/FUL regulate s the transcription of genes required for cellular differentiation dur ing fruit and leaf development.