To exploit ecogeographical niches of the temperate zone, trees and other perennial plant species optimize the timing of floral and vegetative bud break within the dynamic nature of the annual environmental cycle. This insures successful reproduction and continued growth over their lifespan. Adapting to the annual environmental cycle as well as more long-term environmental fluctuations, such as, global warming is critical to insuring survival of the species. Thus, the tree must utilize physiological systems to sense and respond in time and space to the appropriate environmental cues. Historically, many of the physiological players such as phytohormones and their actions have been well characterized, however, the underlying regulation of the genes and gene networks controlling these physiological systems remains relatively unknown. With advances in molecular genetics and genomics technologies, we are beginning to understand the genetic basis for a number of important phenological traits. It is the intent of this review to highlight our current state of knowledge for the genetics of the timing of bud-break in trees focusing on both fruit and forest trees to provide a framework to guide future efforts to understand how the tree coordinates annual growth, development and reproduction with the environmental cycle. Keywords: Bud-break; Dormancy; Epigenomics; Flowering date; Genetics and genomics; microRNAs; Phenological traits; QTL mapping; Transcriptomics; Trees
