Modeling of root nitrate responses suggests preferential foraging arises from the integration of demand, supply and local presence signals

Abstract

A plants' fitness to a large extent depends on its capacity to adapt to spatio-temporally varying environmental conditions. One such environmental condition to which plants display extensive phenotypic plasticity is soil nitrate levels and patterns. In response to heterogeneous nitrate distribution, plants show a preferential foraging response, enhancing root growth in high nitrate patches and repressing root growth in low nitrate locations beyond a level that can be explained from local nitrate sensing. Although various molecular players involved in this preferential foraging behavior have been identified, how these together shape root system adaptation has remained unresolved. Here we use a simple modeling approach in which we incrementally incorporate the various known molecular pathways to investigate the combination of regulatory mechanisms that underly preferential root nitrate foraging. Our model suggests that instead of a thus far not discovered growth suppressing supply signal, growth reduction on the low nitrate side may simply arise from a reduced root foraging and increased competition for carbon. Additionally, our work suggests that the long distance CK signaling involved in root growth increase in high nitrate patches may represent a supply signal specifically functioning in modulating demand signaling strength. We illustrate how this integration of demand and supply signals prevents excessive preferential foraging under conditions in which demand is not met by sufficient supply and a more generic foraging in search of nitrate should be maintained.

The NIN-LIKE PROTEIN 7 (NLP7) transcription factor modulates auxin pathways to regulate root cap development

“…Localized nitrate patches result in an increase in lateral root elongation and density in Arabidopsis (Linkohr et al, 2002; Sun et al, 2017; Liu et al, 2020). Moderate, homogenous nitrate levels promote primary and lateral root growth while high homogenous nitrate levels suppress growth (Asim et al, 2020; Boer et al, 2020; Liu and von Wirén, 2022). Nitrate mediates these functions largely through its impacts on endogenous auxin pathways.…”

Embodiment in distributed information processing: “Solid” plants versus “liquid” ant colonies

“…As an example, more lateral roots branch off where nutrient levels are higher, yet this response to local soil conditions depends both on how much the plant is in need of that nutrient and the extent to which other parts of the root system have failed to locate this nutrient. This integration of local, systemic and long range information depends on the status storage in the local plant organ as well as on the transport of systemic and long-distance signals through the vasculature (Boer et al, 2020; Guan, 2017). In contrast, the continuous moving and mixing of ants in an ant colony makes it impossible to store locational or directional information internally in groups of ants themselves.…”

Modeling of Root Nitrate Responses Suggests Preferential Foraging Arises From the Integration of Demand, Supply and Local Presence Signals

“…We thank Bas van den Herik for helpful discussions. This manuscript has been released as a pre-print at BioRxiv (Boer et al, 2019).…”