Abstract
Root system architecture results from a highly plastic developmental process to adapt to environmental conditions. In particular, the development of lateral roots and root hair growth are constantly optimized to the rhizosphere properties, including biotic and abiotic constraints. The development of the root system is tightly controlled by auxin, the driving morphogenic hormone in plants. Glutathione, a major thiol redox regulator, is also critical for root development but its interplay with auxin is scarcely understood. Previous work showed that glutathione deficiency does not alter root responses to indole acetic acid (IAA), the main active auxin in plants. Because indole butyric acid (IBA), another endogenous auxinic compound, is an important source of IAA for the control of root development, we investigated the crosstalk between glutathione and IBA during root development. We show that glutathione deficiency alters lateral roots and root hair responses to exogenous IBA but not IAA. Detailed genetic analyses suggest that glutathione regulates IBA homeostasis or conversion to IAA in the root cap. Finally, we show that both glutathione and IBA are required to trigger the root hair response to phosphate deprivation, suggesting an important role for this glutathione-dependent regulation of the auxin pathway in plant developmental adaptation to its environment.
Highlights
Root developmental plasticity, combining root growth and root branching, is essential for plants to adapt and optimize their growth in changing environmental conditions, such as nutrient and water availability, rhizosphere microbiome or soil structure heterogeneity
We can conclude that glutathione is required for c the Indole-3-butyric Acid (IBA)-dependent induction of root hairs (RH) growth. s Glutathione levels affect auxin signalling in the basal part of the meristem. nu We have shown that glutathione deficiency alters RH elongation and Lateral root primordia (LRP) density in response to IBA. a We know that root tip-derived indole acetic acid (IAA) transits through the lateral root cap to regulate both founder cell positioning and RH growth in the basal part of the meristem
Glutathione regulation of IBA homeostasis or conversion to IAA in the root cap t In this work, we first report that root hair and lateral root responses to exogenous IBA, but not IAA, ip are impaired by glutathione deficiency
Summary
Root developmental plasticity, combining root growth and root branching, is essential for plants to adapt and optimize their growth in changing environmental conditions, such as nutrient and water availability, rhizosphere microbiome or soil structure heterogeneity. Recent works have reported the critical role of IBA-to-IAA conversion in the root cap as a source of auxin for the oscillatory positioning of LR founder cells IBA-to-IAA conversion taking place in the LR primordium itself likely d participates in further LR development (Strader and Bartel, 2011; Michniewicz et al, 2019) Despite te all these reported functions in root development, the importance of IBA-derived IAA relatively to other IAA sources is still poorly understood and scarcely documented, in case of p changing environmental constraints. Glutathione is a small and stable thiol-containing tripeptide (Glu-Cys-Gly) essential for plant survival and present in large concentrations in cells, up to several millimolar (Noctor et al, 2012) It has many roles, including the detoxification of heavy metals and xenobiotics, sulfur homeostasis, ROS homeostasis and redox signalling. We suggest a c physiological role for this glutathione-dependent IBA response, showing that IBA and glutathione Ac pathways are critical for RH responses to phosphate deficiency
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