Engineering Drought Resistance in Forest Trees

Abstract

Climatic stresses limit plant growth and productivity. In the past decade, tree improvement programs were mainly focused on yield but it is obvious that enhanced stress resistance is also required. In this review we highlight important drought avoidance and tolerance mechanisms in forest trees. Genomes of economically important trees species with divergent resistance mechanisms can now be exploited to uncover the mechanistic basis of long-term drought adaptation at the whole plant level. Molecular tree physiology indicates that osmotic adjustment, antioxidative defense and increased water use efficiency are important targets for enhanced drought tolerance at the cellular and tissue level. Recent biotechnological approaches focused on overexpression of genes involved in stress sensing and signaling, such as the abscisic acid core pathway, and down-stream transcription factors. By this strategy, a suite of defense systems was recruited, generally enhancing drought and salt stress tolerance under laboratory conditions. However, field studies are still scarce. Under field conditions trees are exposed to combinations of stresses that vary in duration and magnitude. Variable stresses may overrule the positive effect achieved by engineering an individual defense pathway. To assess the usability of distinct modifications, large-scale experimental field studies in different environments are necessary. To optimize the balance between growth and defense, the use of stress-inducible promoters may be useful. Future improvement programs for drought resistance will benefit from a better understanding of the intricate networks that ameliorate molecular and ecological traits of forest trees.

Climate sensitivity of Cryptomeria japonica in two contrasting environments: Perspectives from QTL mapping

“…Additionally, this QTL could be closely related to genes associated with growth response to drought stress. Key genes in drought tolerance and adaptation of plant model species (e.g., Arabidopsis thaliana, Populus) and other forest tree species (e.g., Pinus, Picea) have been reported in previous research (reviewed in [64]), and further research with similar approaches on C. japonica is essential to identify the same genes. Furthermore, identifying genes associated with drought stress is of importance for future forest management as climate change is expected to increase the frequency of extreme climatic events, such as drought and heatwaves [1].…”

What Makes the Wood? Exploring the Molecular Mechanisms of Xylem Acclimation in Hardwoods to an Ever-Changing Environment

“…The effects of drought on xylogenesis have been studied on several angiosperm species over the last decade. Poplar, in particular, was intensely studied [46,47]. Cambial cell layers are reduced under drought compared to well-watered plants [10,48].…”

“…Further functional analyses by forward and reverse genetic approaches are required to understand the acclimatory responses of trees to salt stress in more detail. While a number of candidate genes has already been studied for their involvement in enhancing salt tolerance in leaves or roots [47], systematic genetic studies targeting at enhanced xylem salt resistance are lacking.…”

Molecular study of drought response in the Mediterranean conifer Pinus pinaster Ait.: Differential transcriptomic profiling reveals constitutive water deficit‐independent drought tolerance mechanisms

“…Plant responses to water stress are a complex process that is controlled by multiplex regulatory events involving signaling, ion transport, and transcription regulation to control cell turgor loss, increase in solute concentration, reduction of relative water content, and cell membranes shrinkage, which alters interactions with the cytoskeleton and cell wall (Haswell & Verslues, 2015). In response to soil dehydration, concentration of endogenous abscisic acid (ABA) progressively increases activating a cascade of physiological responses, including stomatal closure, one of the earliest plant responses (Osakabe, Shinozaki, & Tran, 2014; Polle, Chen, Eckert, & Harfouche, 2019). This compound is produced in stressed roots and transported to leaves to regulate stomatal aperture (Schachtman & Goodger, 2008).…”