Functional Annotation of the Central Circadian Clock Components in Eucalyptus and Populus

The plant circadian clock regulates numerous agriculturally important traits through imparting predictive information such as time of day or season, and components of the clock have been implicated to be major contributors to hybrid vigour. Current research has provided several lines of evidence linking the clock to regulation of carbon metabolic processes during xylogenesis. In trees, however, where this ecologically and economically important tissue acts as the major carbon sink, the relationship remains poorly understood. Our study thus aims to further explore the role of the clock in two forestry tree species, Populus trichocarpa and Eucalyptus grandis, through functional annotation of Arabidopsis circadian clock gene homologs, with a focus on the roles of these components in xylem development. We present a complete analysis of the evolution and nomenclature of all major components of the clock, as well as spatiotemporal expression dynamics of core and duplicated genes. We observe a general conservation of the basic clock mechanism between these diverse plant clades, but also describe evidence of diversification and sub-functionalization in some members, using xylem expression evidence from several hundred individuals of two inter-specific backcross families of E. grandis and E. urophylla.