A new class of plastidic phosphate translocators: a putative link between primary and secondary metabolism by the phosphoenolpyruvate/phosphate antiporter.

Abstract

We have purified a plastidic phosphate transport protein f r o m maize endosperm membranes and cloned and sequenced the corresponding cDNAs from maize endosperm, , maize roots, cauliflower buds, tobacco leaves, and Arabidopsis leaves. All of these cDNAs exhibit high homology t a e a c h other but only -30% identity to the known chloroplast triose phosphate/phosphate translocators. The corresporrding genes are expressed in both photosynthetically active tissues and in nongreen tissues, although transcripts were more abundant in nongreen tissues. Expression of the coding region in transformed yeast cells and subsequent transport measurements of the purified recombinant translocator showed that the protein mediates transport of inorganic phosphate in exchange with C3 compounds phosphorylated at C-atom 2, particularly phosphoenolpyruvate, which is required inside the plastids for the synthesis of, for example, aromatic amino acids. This plastidic phosphate transporter is thus different in structure and function from the known triose phosphate/phosphate translocator. We prsp,ose that plastids contain various phosphate translocators with overlapping substrate specificities to ensure an effici6nt supplyiof plastids with a single substrate, even in the presence of other phosphorylated metabolites.

Sucrose-Starch Conversion in Heterotrophic Tissues of Plants

“…About the same time Heldt and associates (1991) reviewed diverse specificities of translocators in various types of plastids. More recently, several reports have shown the existence of different types of phosphate translocators in various types of plastids (Schüne-mann and Borchert, 1994;Batz et al, 1995;Quick and Neuhaus, 1996;Fischer et al, 1997;Kammerer et al, 1998).…”

Metabolite transport and associated sugar signalling systems underpinning source/sink interactions

“…Another type of phosphate transporter (PPT) facilitates the transport of three-carbon compounds containing a phosphate group at the C2 position, such as phospho enol pyruvate (PEP) and 2-phosphoglyceratefor phosphate across the inner plastid envelope membrane in heterotrophic tissues [52]. PPT transporters are essential for the transport of PEP into plastids, which with the exception of lipid-storage tissues, cannot produce PEP [53].…”

Role of metabolite transporters in source-sink carbon allocation

“…The plastid sodium-dependent pyruvate transporter BASS2 was found to import pyruvate into plastids (“11” in Figure 2; Furumoto et al, 2011). Alternatively, pyruvate can be produced from PEP that could either be formed within the plastid stroma (Flügge et al, 2011) or imported by the PEP/phosphate translocator (PPT; “12” in Figure 2; Fischer et al, 1997). Moreover, malate can also serve as a precursor for stromal pyruvate.…”