Abstract
Inorganic phosphate is one of key macronutrients essential for plant growth. The acquisition and distribution of phosphate are mediated by phosphate transporters functioning in various physiological and biochemical processes. In the present study, we comprehensively evaluated the phosphate transporter (PHT) gene family in the latest release of the Populus trichocarpa genome (version 3.0; Phytozome 11.0) and a total of 42 PHT genes were identified which formed five clusters: PHT1, PHT2, PHT3, PHT4, and PHO. Among the 42 PHT genes, 41 were localized to 15 Populus chromosomes. Analysis of these genes led to identification of 5–14 transmembrane segments, most of which were conserved within the same cluster. We identified 234 putative cis elements in the 2-kb upstream regions of the 42 PHT genes, many of which are related to development, stress, or hormone. Tissue-specific expression analysis of the 42 PtPHT genes revealed that 25 were highly expressed in the roots of P. tremula, suggesting that most of them might be involved in Pi uptake. Some PtPHT genes were highly expressed in more than six of the twelve investigated tissues of P. tremula, while the expression of a few of them was very low in all investigated tissues. In addition, the expression of the PtPHT genes was verified by quantitative real-time PCR in four tissues of P. simonii. Transcripts of 7 PtPHT genes were detected in all four tested tissues of P. simonii. Most PtPHT genes were expressed in the roots of P. simonii at high levels. Further, PtPHT1.2 and PtPHO9 expression was increased under drought conditions, irrespective of the phosphate levels. In particular, PtPHT1.2 expression was significantly induced by approximately 90-fold. However, the transcriptional changes of some PtPHT genes under drought stress were highly dependent on the phosphate levels. These results will aid in elucidation of the functions of PtPHT in the growth, development, and stress response of the poplar plant.
Highlights
Phosphorus is a major macronutrient required for plant growth and development
We identified a total of 42 putative PtPHT genes, including 12 PHO, 14 PtPHT1, 2 PtPHT2, 6 PtPHT3, and 8 PtPHT4 genes from the genome of P. trichocarpa according to the full AtPHT family in Arabidopsisf (Table 1)
PtPHT genes in the roots of P. simonii were examined at varying phosphate levels
Summary
It constitutes up to 0.2% of the dry weight of plant cells and is required in significant quantities (Schachtman et al, 1998). It is often a limiting factor for plant growth because the soil inorganic phosphate (Pi) concentration is usually lower than 10 μM (Shen et al, 2011). Plants have evolved specific transport systems for the uptake and partitioning of Pi (Poirier and Bucher, 2002). Both low- and high-affinity Pi-transporter systems have been identified in plants (Clark et al, 2000; Misson et al, 2004). The genes encoding for low-affinity Pi transport are constitutively expressed and function at relatively high Pi in the millimolar range, whereas high-affinity Pi transporters are transcriptionally induced at low Pi levels in the micromolar range (Raghothama, 2000)
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