AUTHOR=Sagor G. H. M. , Zhang Siyuan , Kojima Seiji , Simm Stefan , Berberich Thomas , Kusano Tomonobu 

TITLE=Reducing Cytoplasmic Polyamine Oxidase Activity in Arabidopsis Increases Salt and Drought Tolerance by Reducing Reactive Oxygen Species Production and Increasing Defense Gene Expression

JOURNAL=Frontiers in Plant Science

VOLUME=7

YEAR=2016

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2016.00214

DOI=10.3389/fpls.2016.00214

ISSN=1664-462X

ABSTRACT=<p>The link between polyamine oxidases (PAOs), which function in polyamine catabolism, and stress responses remains elusive. Here, we address this issue using <italic>Arabidopsis pao</italic> mutants in which the expression of the five <italic>PAO</italic> genes is knocked-out or knocked-down. As the five single <italic>pao</italic> mutants and wild type (WT) showed similar response to salt stress, we tried to generate the mutants that have either the cytoplasmic PAO pathway (<italic>pao1 pao5</italic>) or the peroxisomal PAO pathway (<italic>pao2 pao3 pao4</italic>) silenced. However, the latter triple mutant was not obtained. Thus, in this study, we used two double mutants, <italic>pao1 pao5</italic> and <italic>pao2 pao4</italic>. Of interest, <italic>pao1 pao5</italic> mutant was NaCl- and drought-tolerant, whereas <italic>pao2 pao4</italic> 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 (<italic>pao1 pao5</italic>) 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 <italic>Arabidopsis</italic> plant silencing cytoplasmic <italic>PAO</italic>s shows salinity tolerance by reducing ROS production and strongly inducing subsets of stress-responsive genes under stress conditions.</p>