Characterization of promoter expression patterns derived from the Pht1 phosphate transporter genes of barley (Hordeum vulgare L.)

Abstract

By comparison with dicot plant species, relatively little work has been reported on the phosphate transporter (Pht1) gene family from monocot species. Initial studies have shown that barley contains at least eight homologous genes. The promoters of six of these genes were analysed for the presence of regulatory elements potentially associated with expression specificity. In particular, the P1BS-like elements (implicated in phosphorus-regulated expression of genes in plants) was identified in all HvPht1 promoters examined. For two members of the family (HvPht1;1 and HvPht1;2), promoter fusions to beta-glucuronidase and green fluorescent protein reporter genes were constructed, transformed into rice, and the expression profiles observed. The inclusion of an intron derived from Adh1 enhanced gene expression approximately 20-fold, but did not appear to affect the specificity of expression. The HvPht1;1 and HvPht1;2 promoters showed minor differences in expression patterns but, in general, expression was observed at high levels in trichoblast cells (root hairs) and stele of the nodal root, throughout secondary roots, and at a relatively low level in leaf tissues. Under phosphorus deficiency, expression was induced by up to 5-fold. These observations are consistent with a primary role for the encoded genes in the uptake of phosphate by root hairs from soil solution and further current understanding of the mechanisms involved. The promoters also have application for providing a new resource for cereal transformation, ideally suited for driving the expression of foreign genes associated with nutrient uptake.

Promoter Analysis of the Barley Pht1;1 Phosphate Transporter Gene Identifies Regions Controlling Root Expression and Responsiveness to Phosphate Deprivation

“…The HvPht1;1 promoter, designated here as fulllength HvPht1;1, is derived from the 1,400 nucleotides immediately upstream from the translation start of the HvPht1;1 gene (GenBank accession number AF543197) and has been described previously (Schü nmann et al, 2004). A promoter deletion series was prepared as outlined in Figure 1A and used to generate reporter gene constructs (Fig.…”

“…Several motifs were identified, including a motif similar to the putative P-responsive P1BS element (GnATATnC) identified by Rubio et al (2001). The P1BS-like motif was present in all HvPht1 promoters for which sequence was available (Pht1;1, Pht1;2, Pht1;4, Pht1;5, Pht1;6, and Pht1;7;Schü nmann et al, 2004). In Arabidopsis a MYB transcription factor, PHR1, has been identified which, when mutated, resulted in impaired P-regulated expression for a range of genes.…”

“…To provide a better understanding of the regulation of the Pi-uptake mechanism, the promoter regions from two of the barley Pht1 genes (HvPht1;1 and HvPht1;2) were investigated using reporter genes (Schü nmann et al, 2004). When transformed into rice (Oryza sativa), the promoters activated highest levels of gene expression in the trichoblast (root hair) cells of the nodal root.…”

“…The promoter regions of the Pht1 genes from barley were also analyzed for the presence of regulatory elements for which there is evidence of a functional role in plants (Schü nmann et al, 2004). Several motifs were identified, including a motif similar to the putative P-responsive P1BS element (GnATATnC) identified by Rubio et al (2001).…”

“…The presence of P1BS-like elements in the HvPht1 promoters suggests that the motif may serve a similar role in monocot promoters. However, P1BS-like elements are also present in multiple copies within the ubiquitin promoter, a promoter which does not respond to P deficiency (Schü nmann et al, 2004), and few cis elements have been shown to be functional in both monocots and dicots. Furthermore, even in Arabidopsis, the element was identified in the promoter regions of 15% to 20% of all genes and was not preferentially in promoters of P-regulated genes (Hammond et al, 2003).…”