Dissecting iron deficiency‐induced proton extrusion in Arabidopsis roots

Abstract

Summary• Here, we have analysed the H + -ATPase-mediated extrusion of protons across the plasma membrane (PM) of rhizodermic cells, a process that is inducible by iron (Fe) deficiency and thought to serve in the mobilization of sparingly soluble Fe sources.• The induction and function of Fe-responsive PM H + -ATPases in Arabidopsis roots was investigated by gene expression analysis and by using mutants defective in the expression or function of one of the isogenes. In addition, the expression of the most responsive isogenes was investigated in natural Arabidopsis accessions that have been selected for their in vivo proton extrusion activity.• Our data suggest that the rhizosphere acidification in response to Fe deficiency is chiefly mediated by AHA2, while AHA1 functions as a housekeeping isoform. The aha7 knock-out mutant plants showed a reduced frequency of root hairs, suggesting an involvement of AHA7 in the differentiation of rhizodermic cells. Acidification capacity varied among Arabidopsis accessions and was associated with a high induction of AHA2 and IRT1, a high relative growth rate and a shoot-root ratio that was unaffected by the external Fe supply.• An effective regulation of the Fe-responsive genes and a stable shoot-root ratio may represent important characteristics for the Fe uptake efficiency.

H+‐pyrophosphatase IbVP1 promotes efficient iron use in sweet potato [Ipomoea batatas (L.) Lam.]

“…Changes in the rhizosphere represent a central mechanism in plant mineral nutrition, contributing to nutrient solubility and proton‐motive force (Li et al ., 2015; Palmgren, 2001; Palmgren, 1998; Santi and Schmidt, 2009; Zhu et al ., 2009). The increase in root iron precipitation, Fe content and FCR activity in the IA lines demonstrated regulation of Fe uptake, which is associated with the up‐regulation of key genes such as FRO2 , IRT and FIT involved in Fe acquisition (Figure 8).…”

“…In addition, the expression of other Fe uptake genes is increased in response to altered levels of hormones (e.g. auxin; Schmidt et al ., 2000; Santi and Schmidt, 2008, 2009; Bacaicoa et al ., 2011; Kabir et al ., 2013), carbohydrates (e.g. sucrose; Zargar et al ., 2015; Lin et al ., 2016) and reactive oxygen species (ROS; Molassiotis et al ., 2006; Donnini et al ., 2011), explaining the diverse effects of Fe deficiency on plant development and growth (Briat et al ., 2015; Kobayashi and Nishizawa, 2012).…”

iTRAQ Protein Profile Analysis of Arabidopsis Roots Reveals New Aspects Critical for Iron Homeostasis

“…Remarkably, six proteins of the Met cycle, the SAM synthetases MAT1, MAT2, MAT3, and MAT4, the cobalmine-independent Met synthase ATMS1, and the S-adenosyl-Lhomo-Cys hydrolase SAHH1, were found among the most abundant proteins, underlining the importance of this pathway in roots. The most abundant plasma membrane-bound protein identified in both biological replicates was the P-type ATPase AHA2, one of the two major H + -ATPases in roots (Santi and Schmidt, 2009;Supplemental Table S1). …”

“…The acquisition of Fe is aided by the induction of ARABIDOPSIS H + ATPASE2 (AHA2), a plasma membrane-bound proton pump whose activity decreases the extracellular pH and thereby increases the solubility of Fe in the apoplast and in the rhizosphere (Santi and Schmidt, 2009). Induction of AHA2 occurs somewhat later than that of IRT1 and FRO2 and is not controlled by FIT, indicating separate control of Fe mobilization and uptake.…”

Proteasome‐mediated turnover of the transcriptional activator FIT is required for plant iron‐deficiency responses

“…Although abundant in nature, iron is often available in limited quantities because it is mostly present in rather insoluble Fe(III) complexes in soil. The model plant Arabidopsis thaliana copes with iron deficiency by increasing root H + -ATPase activity, encoded by the AHA2 gene in Arabidopsis, to lower the rhizosphere pH and increase Fe(III) solubility (Santi and Schmidt, 2009). The inducible root ferric-chelate reductase activity encoded by the FRO2 gene reduces Fe(III) to the more soluble Fe(II) form (Robinson et al, 1999).…”