Role of GOBLET and Auxin in Controlling Organ Development and Patterning

The size and shape of plant leaves are extremely diverse within and among species, and are also sensitive to growth conditions. Compound leaves, such as those of tomato, maintain morphogenetic activity during early stages of their development, enabling them to elaborate lateral appendages such as leaflets. The aim of the research project was to understand the interaction between the plant hormone auxin, the putative auxin response inhibitor ENTIRE (E, SlIAA9) and the NAM/CUC transcription factor GOBLET (GOB) in compound-leaf development in tomato (Solanum lycopersicum). The specific aims of the project were: 1. Investigation of the role of GOB in compound-leaf development. 2. Characterization of E function in auxin signaling. 3. Characterization of the role of auxin in compound-leaf development. 4. Investigation of the genetic and molecular interaction between E and GOB. 5. Investigate the role of these factors in fruit development. There were no major changes in these objectives. GOB was shown to mark and promote the boundaries between the leaf and initiating leaflets. Its accurate distribution was found to be required for proper leaflet initiation and separation. E was found to interact with the TIR1 and AFB6 proteins in an auxin-dependant manner, indicating that these are functional auxin receptors that mediate E degradation in the presence of auxin. This was further supported by the stabilization of E by a mutation in domain II of the protein, which is thought to mediate its auxin-dependant degradation. Over expression of this stabilized form in tomato leaves and characterization of the e mutant phenotype and the E expression domain indicated that E acts between initiating leaflets to inhibit auxin response and lamina growth. Generation and analysis of tomato plants expressing the auxin response reporter DR5::VENUS, and analysis of the effect of auxin microapplication or overexpression of an auxin biosynthesis gene, indicated that auxin marks the sites of leaflet initiation and promotes lamina growth. Investigation of the molecular and genetic interaction between auxin, GOB and E revealed a complex network of mutual regulation that is utilized to precisely pattern the leaf margin in a manner that enables the combination of tight control and flexibility. E, auxin and GOB were shown to affect fruit development and fruit set, and in an extension of the project are currently utilized to identify new players that affect these processes. The research project yielded enhanced understanding of the mechanisms of compound leaf patterning and provided tools that will enable the manipulation of leaf shape and fruit set.