| Ripening is a key process in agriculture because it leads to the production of attractive, tasteful and healthy compound-containing fruits for consumption. In tomato, a model for fleshy fruit genomics, ripening is regulated by a number of transcription factors (TFs) in conjunction with the plant hormone ethylene, while suppressing other ethylene responses. The presence of an intricate regulatory network underlying the process is evident from a large number of mutations affecting ethylene signalling or transcription factor activity that lead to defective ripening. Yet, the topology and internal interactions of this network are far from understood. To further understand this network is the challenge addressed in this proposal. I intend to characterize in particular two TFs, CNR and SlAP2, which regulate each other?s expression in opposite ways. Mutations affecting their activity have major effects on ripening and they are therefore considered major players in the ripening regulatory network. The direct target genes of these TFs will be identified. By identifying and comparing target genes of CNR and SlAP2 in wild type and in an ethylene-insensitive mutant I intend to separate ethylene-dependent and ?independent regulatory processes. Furthermore, proteomics studies will be used to identify the protein-protein interactions of the two regulatory TFs and to understand the role of these interactions in their respective, and possibly overlapping functions. A regulatory role of SlAP2 in the synthesis of the plant hormone brassinosteroid, suggested by the down regulation of brassinosteroid synthesis genes in the absence of SlAP2 protein will be further investigated. Brassinosteroid production was demonstrated in fruits but the function there is yet unknown, while the link with SlAP2 suggests a role in ripening. Identifying the direct and indirect targets of SlAP2 and CNR will highlight the respective positions, functional roles, and interactions of CNR and AP2 in the regulatory network controlling fruit ripening. |
