Abstract
In higher plants, plastidic phosphate translocators are classified into four subfamilies according to their substrate specificity; triosephosphate/phosphate translocator (TPT), phosphoenolpyruvate/phosphate translocator (PPT), glucose 6-phosphate/phosphate translocator (GPT) and xylulose 5-phosphate/phosphate translocator. From the inducible Crassulacean acid metabolism (CAM) plant Mesembryanthemum crystallinum, we have detected four kinds of cDNAs (TPT1, PPT1, GPT1 and GPT2) belonging to three of these subfamilies. During C3-CAM transition of M. crystallinum by salt stress, the transcript levels of TPT1 in leaves are relatively unchanged while those of other three transcripts are dramatically increased.
To characterize transport characteristics of the translocators we obtained crude membranes containing recombinant proteins of TPT1, GPT1 and GPT2 expressed in yeast cells. These proteins were reconstituted into liposomes for subsequent determination of their transport activities. At present, we have confirmed that recombinant TPT1 and GPT2 proteins transported inorganic phosphate. Their transport activities for other substrates will also be reported.
