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.

The epidemiological dynamics followed by viruses in protected horticultural crops in the Mediterranean Arc of Spain has evolved from a majority of those transmitted by aphids to the predominance of whitefly-transmitted ones. Later, due to the shift towards an integrated control that has been quite successful in the control of aleyrodids, not so much in the control of aphids, aphid-borne viruses are having a significant revival in open field cultivation. Another threat is the continuous emergence of new species or variants of mechanically transmitted viruses. Thus, the number of viruses affecting these crops is constantly increasing and their control demands dynamic actions. The main measures that have managed to limit the damage of these diseases have been the improvement in the physical barriers that limit the spread of vectors and the introduction of resistances in the germplasm. Recently, the increased movement of plant materials and of people, the popularity of growing local crop varieties that lack natural resistances against pathogens, and the prospects of global climate change, may well have boosted the frequency of diseases and pests. Faced with this picture, strategies must be addressed from a multidisciplinary approach. The need for in-field diagnostics tools, easy access to information, novel breeding technologies and alternatives to control of these viruses are discussed.