Biotechnological adaptation of high-yielding, gibberellin-overproducing Populus trees to seasonal growth patterns.

Tree growth is central to both terrestrial ecology and the forestry industry. Biotechnology for inducing the overproduction of phytohormones such as gibberellins (GAs) is a powerful tool for improving tree yield and wood properties. Augumentation of GAs in trees in temperate and boreal regions, however, prevents the induction of vegetative dormancy, which results in reduced yield and tree loss over time. Hybrid Populus trees (Populus tremula × P. tremuloides; Ptt) use an internal circadian clock to synchronise their daily metabolism and seasonal growth with predictable light and temperature changes in their local environment. This study focused on modulating GA production in Populus to demonstrate the importance of seasonal growth adaptation. Levels of bioactive GAs were modulated in transgenic trees using the endogenous D-TYPE CYCLIN 3;1 promoter (pPttCYCD3), which is regulated by the circadian clock component LATE ELONGATED HYPOCOTYL 2 (PttLHY2). This modulation resulted in both high yield and seasonal growth adaptation. Such work paves the way for the precision breeding of trees with increased yield that are adapted to local climate conditions.