Promoter deletion analysis elucidates the role of cis elements and 5'UTR intron in spatiotemporal regulation of AtPht1;4 expression in Arabidopsis.

The high-affinity phosphate transporter AtPht1;4 (Arabidopsis phosphate transporter1;4) is not only induced in response to inorganic phosphate (Pi) starvation but also preferentially expressed in the roots of Arabidopsis. In this study, we carried out AtPht1;4 promoter deletion analysis to identify regions that control the Pi responsiveness and spatiotemporal expression of the gene. Expression cassettes with truncated promoter fragments cloned to GUS (beta-glucuronidase) coding sequence were developed. Full-length promoter (-2327) and truncations up to -1436 (from the translational start) showed normal expression of GUS in various parts of the plants. The Pi responsiveness and inducibility of the reporter gene remained unaltered. However, deletion of the promoter region containing the first PHR1-binding site (P1BS) motif (-1350) abolished the AtPht1;4 expression in roots but not in aerial parts. A 164-bp region immediately upstream of the transcription start site appears to be sufficient for the basal expression of the gene. Interestingly, the 5'UTR (5' untranslated region) intron exhibited weak promoter activity as evidenced by its ability to drive the expression of AtPht1;4 in stipules and reproductive organs. Further analyses showed that the 5'UTR intron is essential for AtPht1;4 expression in root tips besides enhancing the level of expression in roots during Pi starvation. However, expression of AtPht1;4 in aerial parts of the plant was not influenced by the intron. Together these results suggest that expression of AtPht1;4 in the roots and aerial parts is regulated by independent mechanisms.

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