DEVELOPMENTAL REGULATION OF CELL-INTERACTIONS IN THE ARABIDOPSIS FIDDLEHEAD-1 MUTANT - A ROLE FOR THE EPIDERMAL-CELL WALL AND CUTICLE

Although the plant epidermis serves primarily a protective role, durin g plant development some epidermal cells specialize, becoming competen t to interact not only with pollen but also with other epidermal cells . In the former case, these interactions mediate recognition, germinat ion, and pollen growth responses and, in the latter case, result in in terorgan fusions which, most commonly, alter floral architecture in wa ys that are thought to promote reproductive success. In either case, a ll of the initial signaling events must take place across the cell wal l and cuticle. In Arabidopsis, mutation of the FIDDLEHEAD gene alters the shoot epidermis such that all epidermal cells become competent to participate in both types of interactions. In fdh-1 mutants, epidermal cells manifest not only a contact-mediated fusion response but also i nteract with pollen. Since carpel epidermal derivatives manifest both of these properties, we postulated that fdh-1 epidermal cells were ect opically expressing a carpel-like program. In this report we demonstra te that manifestation of the fdh-1 phenotype does not require the prod uct of the AGAMOUS gene, indicating that the phenotype is either indep endent of the carpel development program or that fdh-1 mutations activ ate a carpel-specific developmental program downstream of the AG gene. furthermore, we demonstrate that plants bearing mutations in the fdh- 1 gene show significant changes in cell wall and cuticular permeabilit y. Biochemical analyses of the lipid composition of the crude cell wal l fraction reveal that fdh-1 cell walls differ from wild-type and mani fest significant changes in high-molecular-weight lipid peaks. These r esults suggest that cell wall and cuticular permeability may be import ant determinants in developmental signaling between interacting cells and implicate lipids as important factors in modulating the selectivit y of the permeability barrier presented by the epidermal cell wall and cuticle. (C) 1997 Academic Press.