Abstract
The soluble form of aluminum (Al) is a major constraint to crop production in acidic soils. The Al exclusion correlated with the Al-induced organic acid is considered as an important mechanism of Al resistance. The regulation of organic acid exudation in response to Al stress mediated by the root organic acid transporters has been extensively studied. However, how plants respond to Al stress through the regulation of organic acid homeostasis is not well understood. In this study, we identified the functionally unknown Transition zone1 (TZ1) as an Al-inducible gene in the root transition zone, the most sensitive region to Al stress, in Arabidopsis. tz1 mutants showed enhanced Al resistance and displayed greatly reduced root growth inhibition. Furthermore, TZ1 was found to interact with the aconitases (ACOs) which can catalyze the conversion from citrate, one of the most important organic acids, into isocitrate. Consistently, in tz1 mutants, the citric acid content was highly increased. Collectively, this study provides evidence to show that TZ1 negatively regulates root growth response to Al stress through interacting with ACOs and regulating citric acid homeostasis.
Highlights
Aluminum (Al) is a prevalent kind of metal elements in the soil and most of the aluminum is in silicate or other solid forms, which are non-toxic to plants
To identify new factors involved in Al resistance, especially in the root transition zone (TZ), we treated the 7-day-old wild type (WT) Arabidopsis seedlings with or without 25μM AlCl3 for 3 h and performed transcriptome analyses with root tissues
We characterized Transition zone1 (TZ1) which was upregulated by Al stress in the TZ to be a negative regulator of Al resistance in Arabidopsis (Figures 1, 2)
Summary
Aluminum (Al) is a prevalent kind of metal elements in the soil and most of the aluminum is in silicate or other solid forms, which are non-toxic to plants. Al toxicity is a major limiting factor that reduces crop yields worldwide and constrains the food security, especially in the developing countries in tropical and subtropical regions abundant with acidic soils (Kochian et al, 2015). Based on the previous studies, plants have developed two main mechanisms to deal with the Al stress: (1) Al exclusion mechanism, in which Al is prevented from entering the plant root apex and (2) Al tolerance mechanism, which involves the detoxification and sequestration of the internal. The most widely documented Al exclusion mechanism is Al-induced release of organic compounds, specially the diverse organic acid ions, such as malate, citrate, and oxalate, to chelate toxic Al3+ in rhizosphere by forming non-toxic compounds and prevent Al3+ from entering the root cell (Kochian et al, 2015). Previous studies have shown that the Cys2His2-type zinc finger transcription factor STOP1 could stimulate ALMT1 and MATE1 expression under Al stress (Iuchi et al, 2007; Liu et al, 2009; Wu et al, 2019; Zhang et al, 2019; Huang, 2021; Xu et al, 2021)
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