Members of the PHO1 gene family show limited functional redundancy in phosphate transfer to the shoot, and are regulated by phosphate deficiency via distinct pathways

Abstract

SummaryThe PHO1 family comprises 11 members in Arabidopsis thaliana. In order to decipher the role of these genes in inorganic phosphate (Pi) transport and homeostasis, complementation of the pho1 mutant, deficient in loading Pi to the root xylem, was determined by the expression of the PHO1 homologous genes under the control of the PHO1 promoter. Only PHO1 and the homologue PHO1;H1 could complement pho1. The PHO1;H1 promoter was active in the vascular cylinder of roots and shoots. Expression of PHO1;H1 was very low in Pisufficient plants, but was strongly induced under Pi-deficient conditions. T-DNA knock-out mutants of PHO1;H1 neither showed growth defects nor alteration in Pi transport dynamics, or Pi content, compared with wild type. However, the double mutant pho1/pho1;h1 showed a strong reduction in growth and in the capacity to transfer Pi from the root to the shoot compared with pho1. Grafting experiments revealed that phenotypes associated with the pho1 and pho1/pho1;h1 mutants were linked to the lack of gene expression in the root. The increased expression of PHO1;H1 under Pi deficiency was largely controlled by the transcription factor PHR1 and was suppressed by the phosphate analogue phosphite, whereas the increase of PHO1 expression was independent of PHR1 and was not influenced by phosphite. Together, these data reveal that although transfer of Pi to the root xylem vessel is primarily mediated by PHO1, the homologue PHO1;H1 also contributes to Pi loading to the xylem, and that the two corresponding genes are regulated by Pi deficiency by distinct signal transduction pathways.

Phosphate (Pi) Starvation Effect on the Cytosolic Pi Concentration and Pi Exchanges across the Tonoplast in Plant Cells: An in Vivo 31P-Nuclear Magnetic Resonance Study Using Methylphosphonate as a Pi Analog

“…It would also be desirable to precisely delineate the temporal sequence of the cell response to cyt sol -Pi drop. This includes the expression of Pi starvation signaling proteins (Fang et al, 2009), the expression of high-affinity Pi transporters (Muchhal and Raghothama, 1999), the replacement of phospholipids with lipids devoid of phosphorus (Dö rmann and Benning, 2002;Jouhet et al, 2003), and more generally the expression (Stefanovic et al, 2007) and transcription (Misson et al, 2005;Tran and Plaxton, 2008) of numerous genes involved in Pi metabolism and associated with the Pi deficiency response.…”

Sugar Signaling in Root Responses to Low Phosphorus Availability

“…Several SPX domain-containing proteins have been implicated in plant responses to low P availability. The expression of genes encoding the SPX domaincontaining proteins AtPHO1 and AtPHO1;H1 and a rice ortholog, OsPHO1;2, is up-regulated during P starvation, and these proteins are thought to regulate rootto-shoot translocation of Pi via the xylem (Stefanovic et al, 2007;Secco et al, 2010). Of the two Arabidopsis PHO1 proteins, only AtPHO1;H1 contains a PHR1-binding site and is dependent on PHR1 for its induction.…”

A Rice cis-Natural Antisense RNA Acts as a Translational Enhancer for Its Cognate mRNA and Contributes to Phosphate Homeostasis and Plant Fitness

“…The Arabidopsis pho1 null mutant shows a strong reduction of Pi loading into the xylem and displays a typical Pi-deficient phenotype in aerial parts of the plant, resulting in an overall reduction in shoot growth and seed yield (Hamburger et al, 2002). The expression of Arabidopsis PHO1 and the steady state level of PHO1 are increased under Pi deficiency (Stefanovic et al, 2007).…”