The response of Arabidopsis root water transport to a challenging environment implicates reactive oxygen species- and phosphorylation-dependent internalization of aquaporins

Abstract

stimulus of Lp r in Arabidopsis. Since both NaCl and SA treatments increased the accumulation of ROS in roots, it was hypothesized that H 2 O 2 or other ROS may have a central role in the regulation of root water transport in response to various biotic or abiotic stimuli. When Arabidopsis roots were treated with mM concentrations of exogenous H 2 O 2 , Lp r was inhibited within minutes by up to 90%. These findings are consistent with previous reports showing that ROS can downregulate water transport in cucumber and maize roots or in the algae Chara corallina. 4-7 H 2 O 2 and possibly other derived ROS may modulate the Lp r through signaling mechanisms or by a direct oxidative gating of aquaporins. The latter hypothesis, which has been favored in previous studies by Steudle and colleagues,6,7 was investigated by Boursiac et al., by functionally expressing aquaporins in Xenopus oocytes and by testing their sensitivity to external H 2 O 2 . The results show that Arabidopsis aquaporins are insensitive to direct oxidation by H 2 O 2 or hydroxyl radicals. Thus, these and complementary pharmacological analyses on excised roots rather support a role for H 2 O 2 as a second messenger that connects environmental stimulus perception to water transport regulation in plant roots. The additional finding that H 2 O 2 can be transported by aquaporins 8,9 opens the possibility of intricate loop mechanisms whereby these proteins may interfere with their own regulation. For example, active PIP aquaporins could facilitate the diffusion within the cell of NADPH-oxidase derived apoplastic H 2 O 2 , which in turn would activate signaling pathways acting on PIP activity and/or subcellular localization.In a previous study, we monitored the subcellular localization of AtPIP1;2 and AtPIP2;1, two of the most abundant PIPs in roots, by expression in transgenic Arabidopsis of fusions with the green fluorescent protein (GFP). 10 We observed that a 100 mM NaCl treatment induced in 2-4 hours an increased intracellular labeling which was interpreted as an intracellular relocalization of the two aquaporins. 10 In our more recent study, both a 150 mM NaCl and a 0.5 mM SA treatments induced an intracellular labeling by GFP-PIP1;2 and PIP2;1-GFP fusions, with a "fuzzy" pattern or at the level of spherical bodies. Preventing the NaCl-or SA-dependent accumulation of ROS with exogenous catalase was able to almost completely counteract the effects of the two stimuli on the localization pattern Aquaporins, which facilitate the diffusion of water across biological membranes, are key molecules for the regulation of water transport at the cell and organ levels. We recently reported that hydrogen peroxide (H 2 O 2 ) acts as an intermediate in the regulation of Arabidopsis root water transport and aquaporins in response to NaCl and salicylic acid (SA). 1 Its action involves signaling pathways and an internalization of aquaporins from the cell surface. The present addendum connects these findings to another recent work which describes multiple phosphorylations...

Coordinated Post-translational Responses of Aquaporins to Abiotic and Nutritional Stimuli in Arabidopsis Roots

“…B, PIP1 proteotypic peptides are PIP12 (loop E), PIP13 , PIP14 , and PIP15 . C, PIP2 proteotypic peptides are PIP21 Arabidopis (22,31), but the present work provides the first evidence of effects of active nitrogen species on root water transport. A role for NO, an important molecule in plant stress signaling, in aquaporin regulation during rice seed germination has been proposed (37).…”

“…This treatment induced a decrease in Lp r by up to 63%, with a half-time of 60 min. The application of H 2 O 2 to excised Arabidopsis root systems was previously shown to induce a timeand dose-dependent decrease in pressure-induced sap flow (J v ), an indicator of Lp r in these conditions (31). In particular, 0.5 mM H 2 O 2 induced a 40% inhibition of J v after 15 min (31).…”

“…The application of H 2 O 2 to excised Arabidopsis root systems was previously shown to induce a timeand dose-dependent decrease in pressure-induced sap flow (J v ), an indicator of Lp r in these conditions (31). In particular, 0.5 mM H 2 O 2 induced a 40% inhibition of J v after 15 min (31). Here, we probed the effects on J v of NO, another oxidative treatment, using DEA-NO as a NO donor molecule.…”

Regulation of Seed Germination and the Role of Aquaporins under Abiotic Stress

“…The reduction in root hydraulic conductivity is also correlated with a dynamic change in the post-translational modifications such as phosphorylation and amidation that affect aquaporin function (Khan et al 2015). Aquaporin is also altered by ROS which leads to channel closure through a direct oxidative mechanism (Kourie 1998), and induces internalization of PIPs and reduces hydraulic conductivity through cell signaling mechanisms (Boursiac et al 2008a, Boursiac et al 2008b). …”

Novel Aquaporin Regulatory Mechanisms Revealed by Interactomics

“…Regulation of PIP Trafficking-Osmotic stresses induce a partial internalization of PIPs (34,83) leading to a reduced abundance of PIPs at the root cell surface, which may contribute to a decrease of root water permeability. In addition, stimulus-induced PIP trafficking can be counteracted by reactive oxygen species (ROS) scavengers, in agreement with the central role played by ROS in stress and hormonal signal- Table II.…”