Plant aminopropyltransferases consist of a group of enzymes that transfer aminopropyl groups derived from decarboxylated S-adenosyl-methionine (dcAdoMet or dcSAM) to propylamine acceptors to produce polyamines, ubiquitous metabolites with positive charge at physiological pH. Spermidine synthase (SPDS) uses putrescine as amino acceptor to form spermidine, whereas spermine synthase (SPMS) and thermospermine synthase (TSPMS) use spermidine as acceptor to synthesize the isomers spermine and thermospermine respectively. In previous work it was shown that both SPDS1 and SPDS2 can physically interact with SPMS although no data concerning the subcellular localization was reported. Here we study the subcellular localization of these enzymes and their protein dimer complexes with gateway-based Bimolecular Fluorescence Complementation (BiFC) binary vectors. In addition, we have characterized the molecular weight of the enzyme complexes by gel filtration chromatography with in vitro assembled recombinant enzymes and with endogenous plant protein extracts. Our data suggest that aminopropyltransferases display a dual subcellular localization both in the cytosol and nuclear enriched fractions, and they assemble preferably as dimers. The BiFC transient expression data suggest that aminopropyltransferase heterodimer complexes take place preferentially inside the nucleus.

ElsevierCampos Beneyto, L.; Granell Albert, P.; Tarraga Herrero, S.; López Gresa, MP.; Conejero Tomás, V.; Belles Albert, JM.; Rodrigo Bravo, I.... (2014) AbstractWe have observed that treatments with salicylic acid (SA) or gentisic acid (GA) induced resistance to RNA pathogens such as ToMV and CEVd in tomato and Gynura auriantiaca, respectively. Accumulation of SA and GA has been found to occur in plants infected by these pathogens, thus pointing out a possible defence role of both molecules. To study the molecular basis of the observed induced resistance to RNA pathogens the induction of silencing-related genes by SA and GA was considered. For that purpose, we searched for tomato genes which were orthologous to those described in Arabidopsis thaliana, such as AtDCL1, AtDCL2, AtDCL4, AtRDR1, AtRDR2 and AtRDR6, and we tracked their induction in tomato along virus and viroid infections. We observed that CEVd significantly induced all these genes in tomato, with the exception of ToRDR6, being the induction of ToDCL4 the most outstanding. Regarding the ToMV asymptomatic infection, with the exception of ToRDR2, we observed a significant induction of all the indicated silencing-related genes, being ToDCL2 the most induced gene. Subsequently, we analyzed their transcriptional activation by SA and at the time when ToMV was inoculated on plants. ToDCL2, ToRDR1 and ToRDR2 were significantly induced by both SA and GA, whereas ToDCL1 was only induced by SA. Such an induction resulted more effective by SA treatment, which is in agreement with the stronger SA-induced resistance observed. Our results suggest that the observed delay in the RNA pathogen accumulation could be due to the pre-induction of RNA silencing-related genes by SA or GA. Highlights-Treatments with salicylic acid or gentisic acid induce resistance to RNA pathogens -Induction of tomato silencing-related genes by RNA pathogen infections is studied -Induction of RNA silencing by SA or GA treatments is analysed in tomato plants -New connexions between RNA silencing and the SA or GA response are proposed