Hidden Branches: Developments in Root System Architecture

Abstract

The root system is fundamentally important for plant growth and survival because of its role in water and nutrient uptake. Therefore, plants rely on modulation of root system architecture (RSA) to respond to a changing soil environment. Although RSA is a highly plastic trait and varies both between and among species, the basic root system morphology and its plasticity are controlled by inherent genetic factors. These mediate the modification of RSA, mostly at the level of root branching, in response to a suite of biotic and abiotic factors. Recent progress in the understanding of the molecular basis of these responses suggests that they largely feed through hormone homeostasis and signaling pathways. Novel factors implicated in the regulation of RSA in response to the myriad endogenous and exogenous signals are also increasingly isolated through alternative approaches such as quantitative trait locus analysis.

Plasticity of the Arabidopsis Root System under Nutrient Deficiencies

“…In developmental terms, LRs differ from PRs because they originate postembryonically from parental roots (Osmont et al, 2007;Péret et al, 2009). The total number of LRs that is produced depends not only on genetic but also on environmental factors.…”

“…Thus, root growth and architecture are extremely relevant for the plant's adaptation to the growth medium, as they determine the soil volume that a plant is able to explore at a given time. Root system architecture (RSA) represents the spatial arrangement of roots of different ages and orders (Lynch, 1995;Osmont et al, 2007) and is determined by genetic factors and the integration of environmental cues (Malamy, 2005). The genetic component determines the fundamental morphology and blueprint of a plant's root system, whereas environmental cues shape root architecture by modifying the intrinsic genetic program.…”

“…The dynamic modulation of RSA is based on the intrinsic developmental nature of the different components of the root system. In fact, the primary root (PR) is established during embryogenesis, while the lateral roots (LRs) that originate from the PR develop postembryonically (Osmont et al, 2007;Péret et al, 2009). These highly dynamic changes in the overall RSA throughout time finally determine root plasticity and allow plants to efficiently adapt to environmental constraints.…”

“…Nutrient availability can exert a profound impact on RSA by altering the number, length, angle, and diameter of roots and root hairs (for review, see Forde and Lorenzo, 2001;López-Bucio et al, 2003;Malamy, 2005;Osmont et al, 2007). In fact, plants can respond to the heterogenous availability of resources by allocating roots where the most favorable conditions are found (Zhang and Forde, 1998;Linkohr et al, 2002;Remans et al, 2006;Lima et al, 2010;Giehl et al, 2012).…”

SHORT-ROOT Regulates Primary, Lateral, and Adventitious Root Development in Arabidopsis

“…Many dicotyledonous plants like Arabidopsis (Arabidopsis thaliana) have a primary root that repeatedly branches to generate several orders of lateral roots, whereas the root systems of cereal crops such as rice (Oryza sativa) and maize (Zea mays) are predominantly composed of adventitious roots (Hochholdinger et al, 2004;Osmont et al, 2007). Despite these anatomical differences, with the exception of the highest orders, roots from all plant species exhibit indeterminate growth behavior (i.e.…”