The Role of Polyamine Uptake Transporters on Growth and Development of Arabidopsis Thaliana
Transgenic manipulation of polyamine levels has provided compelling evidence that polyamines enable plants to respond to environmental cues by activation of stress and developmental pathways. Here we show that the chloroplasts of A. thaliana and soybeans contain both an arginine decarboxylase, and an arginase/agmatinase. These two enzymes combine to synthesize putrescine from arginine. Since the sequences of plant arginases show conservation of key residues and the predicted 3D structures of plant agmatinases overlap the crystal structure of the enzyme from Deinococcus radiodurans, we suggest that these enzymes can synthesize putrescine, whenever they have access to the substrate agmatine. Finally, we show that synthesis of putrescine by ornithine decarboxylase takes place in the ER. Thus A. thaliana has two, and soybeans have three separate pathways for the synthesis of putrescine. This study also describes key changes in plant phenotypes in response to altered transport of polyamines.