Isolation and characterization of a novel ammonium overly sensitive mutant, amos2, in Arabidopsis thaliana

Abstract

Ammonium (NH(4)(+)) toxicity is a significant agricultural problem globally, compromising crop growth and productivity in many areas. However, the molecular mechanisms of NH(4)(+) toxicity are still poorly understood, in part due to a lack of valuable genetic resources. Here, a novel Arabidopsis mutant, amos2 (ammonium overly sensitive 2), displaying hypersensitivity to NH(4) (+) in both shoots and roots, was isolated. The mutant exhibits the hallmarks of NH(4)(+) toxicity at significantly elevated levels: severely suppressed shoot biomass, increased leaf chlorosis, and inhibition of lateral root formation. Amos2 hypersensitivity is associated with excessive NH(4)(+) accumulation in shoots and a reduction in tissue potassium (K(+)), calcium (Ca(2+)), and magnesium (Mg(2+)). We show that the lesion is specific to the NH(4)(+) ion, is independent of NH(4)(+) metabolism, and can be partially rescued by elevated external K(+). The amos2 lesion was mapped to a 16-cM interval on top of chromosome 1, where no similar mutation has been previously mapped. Our study identifies a novel locus controlling cation homeostasis under NH(4)(+) stress and provides a tool for the future identification of critical genes involved in the development of NH(4)(+) toxicity.

Arabidopsis Plastid AMOS1/EGY1 Integrates Abscisic Acid Signaling to Regulate Global Gene Expression Response to Ammonium Stress

“…S3, E and F). This is distinct from previously described NH 4 + -hypersensitive mutants of Arabidopsis, in which root morphological changes were the most visible phenotype (Qin et al, 2008;Jadid et al, 2011;Li et al, 2012). Considering these results jointly, amos1 emerges as a novel NH 4 + -hypersensitivity mutant, displaying severe leaf chlorosis without any impairment of root growth or root development.…”

“…Mapping was performed as described previously (Peters et al, 2003;Li et al, 2012). In brief, DNA was extracted from 300 mutant F2 individual seedlings, 30 individuals as a mixed DNA pool for preliminary mapping and others for further mapping, and genotyped with known insertion/deletion (InDel) molecular markers (Salathia et al, 2007;Supplemental Table S3).…”

The Kinase CIPK23 Inhibits Ammonium Transport in Arabidopsis thaliana

“…Interestingly, a genomic region harboring the CIPK23 gene is responsible for oversensitivity to ammonium in the ammonium oversensitive2 mutant (Li et al, 2012). The identified T-DNA insertion line SALK_036154C showed hypersensitivity to ammonium and MeA (Figure 1).…”

Nitrogen use efficiency (NUE) in rice links to NH4 + toxicity and futile NH4 + cycling in roots

“…At low NH 4 + concentrations, NH 4 + influx is mediated by a saturable HATS (high-affinity transport system), and at higher, including toxic, concentrations of NH 4 + , it is mediated by a LATS (low-affinity transport system) (Wang et al 1993b;Kronzucker et al 2000;von Wiren et al 2000;Britto and Kronzucker 2006). Moreover, the activity of LATS is apparently not downregulated, indeed might even be upregulated, and could cause higher fluxes with increased nitrogen status of the plant (Wang et al 1993b;Rawat et al 1999;Cerezo et al 2001 Szczerba et al 2008b;Balkos et al 2010;Li et al 2012). In our study, high NH 4 + stimulated free NH 4 + accumulation in both shoot and root of W23 and GD (Fig.…”