Cloning and characterization of four phosphate transporter cDNAs in tobacco

Four distinct cDNAs (NtPT1, NtPT2, NtPT3. and NtPT4) encoding phosphate transporters were isolated from tobacco (Nicotiana tabacum L.). They show high degrees of similarity to known high-affinity phosphate transporters in higher plants. Northern blot analysis using probes specific to NtPT1 and NtPT2 and to NtPT3 and NtPT4 indicated that large quantities of these four transcripts accumulated under phosphate-deficient conditions. The transcripts of NtPT1/2 were detected in immature leaves. mature leaves, old leaves, stems, and roots, while those of NtPT3/4 were detected only in old leaves and roots. When tobacco was grown under phosphate-deficient conditions. the transcripts of NtPT1/2 and NtPT3/4 were systemically enhanced after reduction of the total phosphate concentration in each organ. On the other hand. when phosphate was supplied to phosphate-deficient plants, the transcripts of NtPT1/2 and NtPT3/4 decreased systemically before an increase in total phosphate concentration. These results suggest that high-affinity phosphate transporter genes are controlled at the level of transcription by two regulatory systems: one responds to the internal phosphate status and;the other to the external phosphate status. (C) 2002 Elsevier Science Ireland Ltd. All rights reserved.