Les séminaires ont lieu sur le Campus Montpellier SupAgro/INRA de La Gaillarde (2, place P. Viala Montpellier)
Mercredi 10 juin 2015
Salle 204 (Château) à 11h
Root traits beyond architecture
Institute of Life Science, Université Catholique de Louvain, Belgium
Draye X1, Orman B1, Babé A1, Ligeza A1, Faget M1, Meunier F1, Couvreur V1, Javaux M1, Beeckman T2, Bennett M3
Increasing attention is being devoted to root system architecture (RSA) for the improvement of drought tolerance. The focus is generally set on deep roots, expected to grant access to soil water resources during water deficit episodes. Surprisingly, our quantitative understanding of the role of RSA in the uptake of soil water remains limited, which is mainly due to the complexity of the soil-plant continuum. However, although soil and roots consist of very different media, understanding the distribution of water uptake is a matter of quantifying resistances and gradients of water potential in a common spatial and highly dynamic framework. There are therefore several reasons to adopt a fine-grained 3D modelling approach to explore how the interplay between RSA, root and soil hydraulics determines water uptake patterns. Using quantitative models coupling the hydraulic behaviour of soil and roots in an explicit 3D framework, we show that the contribution of RSA to root water uptake is hardly separable from the hydraulic properties of the roots and of the soil. Simulations have been run in which major attributes of the soil/plant system thought to influence water uptake and its spatial distribution have been varied separately: the soil hydraulic conductivity (Ks), the root hydraulic conductivities (Kr and Kx, respectively radial and axial) and the root architecture. We are currently dissecting in silico the radial hydraulic conductivity of a root segment as a function of features affecting the three components of the composite transport model. Making these models compatible with crop growth models is under way and will help explore how water fluxes driven by soil and plant processes affect soil water availability and uptake throughout a growth cycle. In order to explore how plants shape their root system in the soil, we have used an experimental lateral root repression system based on transient water deficit, in barley (Hordeum vulgare) and maize (Zea mays). We have shown that ABA response pathways are involved in the LR repression that occurs during transient water shortage in the root zone. Expression studies in barley reveal that transient water deficit conditions trigger components of ABA response pathways. In addition, in barley, maize and Arabidopsis, exogenous ABA treatments appear to be sufficient to mimic the repression of LR formation at or before the asymmetric founder cell division that was initially observed under transient deficit. A genetic analysis in Arabidopsis further reveals that LR repression occurs through a SNRK2-6-dependentsignalling cascade acting downstream of ABA perception. Finally, additional experiments show that auxin homeostasis above the root tip zone is altered during the transient ABA treatment. We therefore propose a model in which transient water deficit triggers ABA response pathways that alter auxin accumulation and repress LR formation in both monocots and dicots. This raises ABA as a major downstream intrinsic messenger of environmentally induced repression of LR development to quickly adapt root branching to local variations of soil water content. The conclusion that local soil and roots properties significantly affect whole plant patterns of water uptake calls for a better consideration of rhizosphere processes and root plasticity (e.g. hydropatterning) in the design of root ideotypes for water-limited environments.
Contact : Alexandre Martinière