Abstract
Growth and architectural traits in trees are economically and environmentally important and thus of considerable importance to the improvement of forest and fruit trees. These traits are complex and result from the operation of a number of molecular mechanisms. This review will focus on the regulation of crown architecture, secondary woody growth and adventitious rooting. These traits and processes have significant impact on deployment, management, and productivity of tree crops. The majority of the described work comes from experiments in model plants, poplar, apple, peach, and plum because these species allow functional analysis of the involved genes and have significant genomics resources. However, these studies convincingly show conserved mechanisms for elaboration of specific growth and architectural traits. The conservation of these mechanisms suggest that they can be used as a blueprint for the improvement of these traits and processes in phylogenetically diverse tree crops. We will specifically consider the involvement of flowering time, transcription factors and hormone-associated genes. The review will also discuss the impact of recent technological advances as well as the challenges to the dissection of these traits in trees.
Highlights
Intensive forest plantation can alleviate the harvesting pressure on native forests via allowing production of the same or larger amount of wood on a much smaller land base (Paquette and Messier, 2010)
Branches originate in axillary meristems (AMs) and establishment and outgrowth of AMs has a profound effect on branch characteristics and crown architecture
AM initiation is exclusively characterized in herbaceous plants and there is no information about the effect of these genes in trees
Summary
Intensive forest plantation can alleviate the harvesting pressure on native forests via allowing production of the same or larger amount of wood on a much smaller land base (Paquette and Messier, 2010). Improved genetics through breeding is one, if not the leading factor in this increased productivity (Fenning and Gershenzon, 2002; Ruotsalainen, 2014). Tree breeding is slow due to long generation times, traits that need a long time to evaluate and complex genetic architecture of these traits (Fenning and Gershenzon, 2002). Understanding the involved genetic mechanism could significantly accelerate the process through both conventional breeding and genetic engineering. We review the current knowledge about the molecular mechanisms that underpin three developmental processes in trees with significant impact on intensive plantation deployment, management and growth. The review will focus on mechanisms and genes that can provide positive effects and are of breeding value rather than exhaustively discuss progress in the dissection of each process. The reader will be pointed to reviews that deal with these processes in a more comprehensive manner
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