The Export of Polyamines in Plants Is Mediated By a Novel Clade of Bidirectional Transporters
Ubiquitously existent in nature, polyamines play an important role as signaling compounds in plant responses to both biotic and abiotic stresses. My research has shown that the clade of Arabidopsis thaliana and rice BIDIRECTIONAL AMINO ACID TRANSPORTERS (BAT) function as antiporters of polyamines and amino acids. The method used in this study takes advantage of the genetic resources of the model organism Escherichia coli. A double knockout E. coli strain that is deficient in all polyamine antiporters was created and then used to heterologously express candidate plant transporters AtBAT1.1, AtBAT1.2, and OsBAT1. Inside-out membrane vesicles of these transgenic E. coli cells were generated by ultrasound sonication or French press. A radioisotope assay was then performed using these vesicles to confirm the specificity of the target proteins as polyamine antiporters.
To determine the role of BATs in polyamine homeostasis we tested their GFP fusions by transient expression in Nicotiana benthamiana. The GFP-tagged AtBAT1 and OsBAT1 displayed plastid localization in tobacco leaves by using confocal microscopy. Furthermore, the overexpression of OsBAT1 in A. thaliana wild-type results in novel phenotypes that could have potentially economical usage. This indicates that by altering the expression of a single gene of polyamine transporter, we can manipulate the plants phenotypes similar to natural variations.
Metabolic pathways can be localized to one organelle or distributed across several cellular compartments. Previous work has identified only a single cytosolic pathway for putrescine synthesis in Arabidopsis. Here we show that both A. thaliana and soybeans have a plastid-localized putrescine pathway consisting of an arginine decarboxylase and an agmatinase that combine to synthesize putrescine from arginine.