A phosphate transporter with enhanced expression in proteoid roots of white lupin (Lupinus albus L.)

Two full-length cDNAs encoding putative plant phosphate (P_i) transporters were isolated from proteoid roots of P_i-starved white lupin plants 7 and 10 days after emergence (DAE). The deduced amino acid sequences of LaPT1 and LaPT2 are 75.7% identical and both display the typical 12 membrane spanning domains characteristic of other plant P_i transporters. The LaPT1 transcript was expressed most strongly in -P roots (both normal and proteoid) and less so in -P stems and leaves. Transcripts of LaPT1 were low to nondetectable in +P plants. The LaPT2 transcript was highly expressed in roots in both +P and -P treatments. LaPT1 is much more dramatically induced by P deficiency over time, and is more highly expressed in -P proteoid than -P normal root tissue. In contrast, LaPT2 expression was fairly similar over time and in +P and -P normal and -P proteoid roots. While LaPT1 was expressed only under P deficiency, LaPT2 was uniformly expressed by plants exposed to excess Al and deficiencies of N, Mn, Fe and P. The LaPT1 gene was isolated and shown to have two exons interrupted by one intron. The sequence of the 5′-upstream putative promoter was determined.