Photoperiod‐ and temperature‐mediated control of phenology in trees – a molecular perspective

Summary Trees growing in boreal and temperate regions synchronize their growth with seasonal climatic changes in adaptive responses that are essential for their survival. These trees cease growth before the winter and establish a dormant state during which growth cessation is maintained by repression of responses to growth‐promotive signals. Reactivation of growth in the spring follows the release from dormancy promoted by prolonged exposure to low temperature during the winter. The timing of the key events and regulation of the molecular programs associated with the key stages of the annual growth cycle are controlled by two main environmental cues: photoperiod and temperature. Recently, key components mediating photoperiodic control of growth cessation and bud set have been identified, and striking similarities have been observed in signaling pathways controlling growth cessation in trees and floral transition in Arabidopsis . Although less well understood, the regulation of bud dormancy and bud burst may involve cell–cell communication and chromatin remodeling. Here, we discuss current knowledge of the molecular‐level regulation of the annual growth cycle of woody trees in temperate and boreal regions, and identify key questions that need to be addressed in the future. Contents Summary 511 I. Introduction 511 II. Key developmental stages of the annual growth cycle 512 III. Control of growth cessation and bud set by seasonal cues 513 IV. How does photoperiod control developmental transitions? 513 V. The role of temperature in growth cessation and bud set 517 VI. Establishment and release of bud dormancy 517 VII. Natural variation in the regulation of distinct stages of annual growth cycles in trees 521 VIII. Conclusions 521 Acknowledgements 521 References 521