Abstract
The link between polyamine oxidases (PAOs), which function in polyamine catabolism, and stress responses remains elusive. Here, we address this issue using Arabidopsis pao mutants in which the expression of the five PAO genes is knocked-out or knocked-down. As the five single pao mutants and wild type (WT) showed similar response to salt stress, we tried to generate the mutants that have either the cytoplasmic PAO pathway (pao1 pao5) or the peroxisomal PAO pathway (pao2 pao3 pao4) silenced. However, the latter triple mutant was not obtained. Thus, in this study, we used two double mutants, pao1 pao5 and pao2 pao4. Of interest, pao1 pao5 mutant was NaCl- and drought-tolerant, whereas pao2 pao4 showed similar sensitivity to those stresses as WT. To reveal the underlying mechanism of salt tolerance, further analyses were performed. Na uptake of the mutant (pao1 pao5) decreased to 75% of WT. PAO activity of the mutant was reduced to 62% of WT. The content of reactive oxygen species (ROS) such as hydrogen peroxide, a reaction product of PAO action, and superoxide anion in the mutant became 81 and 72% of the levels in WT upon salt treatment. The mutant contained 2.8-fold higher thermospermine compared to WT. Moreover, the mutant induced the genes of salt overly sensitive-, abscisic acid (ABA)-dependent- and ABA-independent- pathways more strongly than WT upon salt treatment. The results suggest that the Arabidopsis plant silencing cytoplasmic PAOs shows salinity tolerance by reducing ROS production and strongly inducing subsets of stress-responsive genes under stress conditions.
Highlights
Polyamines (PAs) are aliphatic compounds with low molecular masses that are ubiquitously present in all living organisms
We found that the pao1 pao5 double mutant, but not the five single mutants or the pao2 pao4 double mutant, was tolerant to salt and drought stress
We confirmed the transcript levels of the five polyamine oxidases (PAOs) genes in wild type (WT) and the pao mutants by real-time reverse transcriptionpolymerase chain reaction using the primers listed in Supplementary Table S1
Summary
Polyamines (PAs) are aliphatic compounds with low molecular masses that are ubiquitously present in all living organisms. Bacteria primarily contain the PAs putrescine (Put) and spermidine (Spd), whereas some bacteria and mammalian cells contain spermine (Spm; Tabor and Tabor, 1985; Cohen, 1998). In addition to these PAs, plants contain another tetraamine, thermospermine (T-Spm), an isomer of Spm (Knott et al, 2007; Kakehi et al, 2008; Naka et al, 2010; Takano et al, 2012). Accumulating evidence indicates that transgenic plants with increased PA levels (via overexpression of PA biosynthetic genes) have increased abiotic stress tolerance, whereas mutant plants deficient in PA biosynthesis are hypersensitive to abiotic stresses (Urano et al, 2003; Capell et al, 2004; Yamaguchi et al, 2006, 2007; Berberich et al, 2015 and the references therein)
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