Polyamine Oxidase5 Regulates Arabidopsis Growth through Thermospermine Oxidase Activity    

Abstract

The major plant polyamines (PAs) are the tetraamines spermine (Spm) and thermospermine (T-Spm), the triamine spermidine, and the diamine putrescine. PA homeostasis is governed by the balance between biosynthesis and catabolism; the latter is catalyzed by polyamine oxidase (PAO). Arabidopsis (Arabidopsis thaliana) has five PAO genes, AtPAO1 to AtPAO5, and all encoded proteins have been biochemically characterized. All AtPAO enzymes function in the back-conversion of tetraamine to triamine and/or triamine to diamine, albeit with different PA specificities. Here, we demonstrate that AtPAO5 loss-of-function mutants (pao5) contain 2-fold higher T-Spm levels and exhibit delayed transition from vegetative to reproductive growth compared with that of wild-type plants. Although the wild type and pao5 are indistinguishable at the early seedling stage, externally supplied low-dose T-Spm, but not other PAs, inhibits aerial growth of pao5 mutants in a dose-dependent manner. Introduction of wild-type AtPAO5 into pao5 mutants rescues growth and reduces the T-Spm content, demonstrating that AtPAO5 is a T-Spm oxidase. Recombinant AtPAO5 catalyzes the conversion of T-Spm and Spm to triamine spermidine in vitro. AtPAO5 specificity for T-Spm in planta may be explained by coexpression with T-Spm synthase but not with Spm synthase. The pao5 mutant lacking T-Spm oxidation and the acl5 mutant lacking T-Spm synthesis both exhibit growth defects. This study indicates a crucial role for T-Spm in plant growth and development.Polyamines (PAs) are low-molecular mass aliphatic amines that are present in almost all living organisms. Cellular PA concentrations are governed primarily by the balance between biosynthesis and catabolism. In plants, the major PAs are the diamine putrescine (Put), the triamine spermidine (Spd), and the tetraamines spermine (Spm) and thermospermine (T-Spm; Kusano et al.,

Arabidopsis NATA1 acetylates putrescine and decreases defense-related hydrogen peroxide accumulation

“…7B). To date, acetylated polyamines have been reported in only a relatively limited number of plant species (Deagazio et al, 1995;Mesnard et al, 2000;Dufeu et al, 2003;Fliniaux et al, 2004;Kamada-Nobusada et al, 2008;Hennion et al, 2012;Kim et al, 2014). However, this is more likely due to the fact that that these metabolites have not been actively searched for, rather than that they are not present.…”

“…Both necrotrophic and biotrophic pathogens can induce H 2 O 2 production via polyamine oxidation (Marina et al, 2008;Moschou et al, 2009;Angelini et al, 2010), and up-regulation of polyamine biosynthesis has been reported in plants infected with a variety of viral, bacterial, and fungal pathogens (Walters, 2003a(Walters, , 2003b. Arabidopsis PAOs oxidize spermine and spermidine more efficiently than N 1 -acetylspermine and N 1 -acetylspermidine (Moschou et al, 2008;Kim et al, 2014), suggesting that nonacetylated polyamines are more likely to be physiologically relevant substrates of these enzymes.…”

“…Arabidopsis PAOs, on the other hand, function in a polyamine back-conversion pathway; oxidizing the carbon at the exo-side of the N 4 -nitrogen of the triamine spermidine, and the tetraamines spermine and thermospermine, thereby producing putrescine and spermidine, respectively, in addition to 3-aminopropanal and H 2 O 2 ( Fig. 1B; Moschou et al, 2012;Ono et al, 2012;Tavladoraki et al, 2012;Ahou et al, 2014;Kim et al, 2014).…”

“…Five PAO homologs have been identified in Arabidopsis; whereas PAO1 and PAO5 are cytosolic enzymes, PAO2, PAO3, and PAO4 are targeted to the peroxisomes (Kamada-Nobusada et al, 2008;Moschou et al, 2008;Ahou et al, 2014;Kim et al, 2014). Polyamine oxidation by PAOs is a major source of stressinduced H 2 O 2 accumulation in plant tissue (Yoda et al, 2009).…”

The Apoplastic Copper AMINE OXIDASE1 Mediates Jasmonic Acid-Induced Protoxylem Differentiation in Arabidopsis Roots

“…On the basis of the cofactor involved, AOs can be classified into two subclasses: the copper amine oxidases (CuAOs), showing high affinity for Put, and the FAD-dependent polyamine oxidases (PAOs), whose preferred substrates are Spd, Spm, and/or their acetyl derivatives (Cona et al, 2006;Tavladoraki et al, 2012). In Arabidopsis, five PAO genes (AtPAOs) and 10 CuAO genes (AtCuAOs) were identified by database search and in some cases characterized at the protein level (Fincato et al, 2011;PlanasPortell et al, 2013;Ahou et al, 2014;Kim et al, 2014). Among CuAO genes, At4g14940 (The Arabidopsis Information Resource [TAIR] accession no.…”