Regulation of the expression of OsIPS1 and OsIPS2 in rice via systemic and local Pi signalling and hormones

Abstract

Two genes with a common region that is characteristic of the TPSI1/Mt4 family were cloned from a Pi-starvationinduced cDNA library of rice roots using suppression subtracted hybridization (SSH). Based on the consensus sequence of these two genes, members of the TPSI1/Mt4 family were found in maize, wheat and barley. BLAST and a cluster analysis in the eight members of the TPSI1/Mt4 family showed two classes of four genes each among monocots. The first gene from rice was designated OsIPS1 based on a comparison of the consensus sequence with AtIPS1 , and consequently the second gene, which has been previously reported as OsPI1 , was designated OsIPS2 . Accumulation of the mRNA of OsIPS1/2 was examined by northern blotting and quantitative reverse transcriptasepolymerase chain reaction in whole-root and split-root experiments under treatment with phosphate (Pi) and the Pi analogue phosphite (Phi). OsIPS1 showed much higher mRNA accumulation in roots than OsIPS2 , and an opposite trend was seen in shoots. OsIPS1/2 showed both systemic and local responses to Pi starvation, and less than 10% of the overall induced mRNA level was due to the local Pi concentration in roots. The results indicate that Phi may interfere with earlier events in roots that are associated with a local Pi signalling pathway. An analysis of transgenic plants showed that OsIPS1/2 are independently responsive to Pi signalling and are mainly expressed in lateral roots and in the vascular cylinder in the primary root. Exogenous cytokinin (6-BA) almost completely suppressed systemic Pi starvation signalling and partially suppressed local Pi signalling. Exogenous abscisic acid remarkably reduced Pi starvation signalling. In contrast, exogenous auxin enhanced Pi signalling, especially local Pi signalling in roots. Exogenous ethylene (ethyphon) and the ratio of auxin to cytokinins did not appear to affect the expression of these two genes.

OsPHF1 Regulates the Plasma Membrane Localization of Low- and High-Affinity Inorganic Phosphate Transporters and Determines Inorganic Phosphate Uptake and Translocation in Rice

“…1, A-D). The constitutive expression of Pi starvationinduced genes (Hou et al, 2005;Aung et al, 2006;Bari et al, 2006) was also observed in the phf1-1 mutant (Fig. 1E).…”

Phosphate Utilization Efficiency Correlates with Expression of Low-Affinity Phosphate Transporters and Noncoding RNA, IPS1, in Barley

“…miR399-guided cleavage can decrease transcript levels of PHO2, while IPS transcripts can protect HvPHO2 mRNA against miR399-guided degradation (Franco-Zorrilla et al, 2007). A number of factors could have effects on the transcript levels of PHO2, including (1) PHO2 transcription rates under different P conditions, (2) PHO2 mRNA turnover rate, (3) the abundance of different members of the miR399 family (Lin et al, 2008), (4) the abundance of transcripts from different IPS genes, which vary in the conserved 24-nucleotide motif (Hou et al, 2005;Franco-Zorrilla et al, 2007) and the formation of incomplete doublestranded RNA complexes with different stability (Fig. 7, A and B), and (5) four to five complementarity sites for miR399 present in the 5# UTR of PHO mRNA (FrancoZorrilla et al, 2007), since different members of the miR399 family may have preference for these sites (Allen et al, 2005).…”

“…They are a class of non-protein-coding RNAs. Overall sequence identities among IPS genes are relatively low, but 22-to 24-nucleotide sequences are highly conserved among plant species (Hou et al, 2005;Shin et al, 2006). IPS genes are expressed primarily in vascular tissues of roots and shoots (Hou et al, 2005;Shin et al, 2006).…”

“…Overall sequence identities among IPS genes are relatively low, but 22-to 24-nucleotide sequences are highly conserved among plant species (Hou et al, 2005;Shin et al, 2006). IPS genes are expressed primarily in vascular tissues of roots and shoots (Hou et al, 2005;Shin et al, 2006). Five IPS genes are found in the Arabidopsis genome (Franco-Zorrilla et al, 2007), and two IPS genes are present in monocotyledonous species such as rice, maize (Zea mays), and barley (Hou et al, 2005).…”

“…IPS genes are expressed primarily in vascular tissues of roots and shoots (Hou et al, 2005;Shin et al, 2006). Five IPS genes are found in the Arabidopsis genome (Franco-Zorrilla et al, 2007), and two IPS genes are present in monocotyledonous species such as rice, maize (Zea mays), and barley (Hou et al, 2005). The Arabidopsis loss-offunction mutant at4 shows high P accumulation in shoots (Shin et al, 2006).…”