Exploring General and Specific Regulators of Phase Transitions for Crop Improvement

The transition of plants from a juvenile to adult growth phase entails a wide range of changes in growth habit, physiological competence and composition. Strikingly, most of these changes are coordinated by the expression of a single regulator, micro RNA 156 (miR156) that coordinately regulates a family of SBP genes containing a miR156 recognition site in the coding region or in their 3’ UTR. In the framework of this research, we have taken a broad taxonomic approach to examine the role of miR156 and other genetic regulators in phase change transition and its implication to plant development and crop improvement.   We set to: Determine the common and unique factors that are altered upon juvenile to adult phase transition. Determine the functions of select miR156 target genes in tomato and maize, and identify those targets that mediate phase transition. Characterize the role of miR172 and its targets in tomato phase change. Determine the relationships between the various molecular circuits directing phase change. Determine the effects of regulated manipulation of phase change genes on plant architecture and if applicable, productivity.   In the course of the study, a new technology for gene expression was introduced – next generation sequencing (NGS). Hence some of the original experiments that were planned with other platforms of RNA profiling, primarily Affymetrix arrays, were substituted with the new technology. Yet, not all were fully completed. Moreover, once the initial stage was completed, each group chose to focus its efforts on specific components of the phase change program. The Israeli group focused on the roles of the DELAYED SYMPODIAL TERMINATION and FALSIFLORA factors in tomato age dependent programs whereas the US group characterized in detail the role of miR156 (also termed Cg) in other grasses and in maize, its interplay with the many genes encoding miR172.