A Novel fry1 Allele Reveals the Existence of a Mutant Phenotype Unrelated to 5′->3′ Exoribonuclease (XRN) Activities in Arabidopsis thaliana Roots

Abstract

BackgroundMutations in the FRY1/SAL1 Arabidopsis locus are highly pleiotropic, affecting drought tolerance, leaf shape and root growth. FRY1 encodes a nucleotide phosphatase that in vitro has inositol polyphosphate 1-phosphatase and 3′,(2′),5′-bisphosphate nucleotide phosphatase activities. It is not clear which activity mediates each of the diverse biological functions of FRY1 in planta.Principal FindingsA fry1 mutant was identified in a genetic screen for Arabidopsis mutants deregulated in the expression of Pi High affinity Transporter 1;4 (PHT1;4). Histological analysis revealed that, in roots, FRY1 expression was restricted to the stele and meristems. The fry1 mutant displayed an altered root architecture phenotype and an increased drought tolerance. All of the phenotypes analyzed were complemented with the AHL gene encoding a protein that converts 3′-polyadenosine 5′-phosphate (PAP) into AMP and Pi. PAP is known to inhibit exoribonucleases (XRN) in vitro. Accordingly, an xrn triple mutant with mutations in all three XRNs shared the fry1 drought tolerance and root architecture phenotypes. Interestingly these two traits were also complemented by grafting, revealing that drought tolerance was primarily conferred by the rosette and that the root architecture can be complemented by long-distance regulation derived from leaves. By contrast, PHT1 expression was not altered in xrn mutants or in grafting experiments. Thus, PHT1 up-regulation probably resulted from a local depletion of Pi in the fry1 stele. This hypothesis is supported by the identification of other genes modulated by Pi deficiency in the stele, which are found induced in a fry1 background.Conclusions/SignificanceOur results indicate that the 3′,(2′),5′-bisphosphate nucleotide phosphatase activity of FRY1 is involved in long-distance as well as local regulatory activities in roots. The local up-regulation of PHT1 genes transcription in roots likely results from local depletion of Pi and is independent of the XRNs.

The Phosphate Fast-Responsive Genes PECP1 and PPsPase1 Affect Phosphocholine and Phosphoethanolamine Content

“…PPsPase1 and PECP1 are listed as strongly induced in several transcriptomics studies related to phosphate starvation (Misson et al, 2005; Bari et al, 2006;Müller et al, 2007;Thibaud et al, 2010;Hirsch et al, 2011). However, very little is known about their precise expression patterns.…”

“…Our inability to reproduce this phenotype may be due to a different light quality or another unidentified factor and could suggest that the phenotype is not strictly linked to Pi starvation. (Hirsch et al, 2011). Left, transmitted light image; center, luminescence signal (color-coded intensity); right, overlay.…”

Rapid Recovery Gene Downregulation during Excess-Light Stress and Recovery in Arabidopsis

“…We have previously found that the nuclear-localized 5ʹ-3ʹ XRN2 and XRN3 function downstream of the chloroplastic SAL1 enzyme in an excess-light and drought stress retrograde signaling pathway. These mutants also exhibit constitutive activation of a significant portion of the excess-lightresponsive transcriptome and possess increased abiotic stress tolerance (Wilson et al, 2009;Estavillo et al, 2011;Hirsch et al, 2011); one possibility is that these phenotypes are due to altered stress recovery dynamics.…”

Identification of Phosphatin, a Drug Alleviating Phosphate Starvation Responses in Arabidopsis

“…The GeneTrap line used for the screen, pht1;4-1, contains a GUS transcriptional fusion with the endogenous PHT1;4 gene, which allows monitoring of its expression (Misson et al, 2004;Hirsch et al, 2011). For the screen, seedlings were grown on Pi-rich medium (+Pi, 500 mM) for the first 5 d. Following this, seedlings were transferred on to Pi-limiting medium (-Pi, 15 mM) with or without the compounds for an additional 5 d. GUS staining was subsequently performed to monitor the expression of PHT1.4.…”

“…A chemical screen for regulators of PHT1;4, expression, a highaffinity Pi transporter used as an early marker of Pi starvation (Karthikeyan et al, 2002;Misson et al, 2004;Hirsch et al, 2011) identified a small family of compounds that were called Phosphatins (PTNs; Pi starvation inhibitor). PTN molecules were shown to alleviate numerous Pi starvation responses and provide a measure of the importance of genetic versus metabolic impacts of Pi starvation.…”