Os07g0438800

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Annotated Information

Summary

• OsPHR2 located on chromosome 7, positioning within the nucleus, encoding a 426 amino acid composition of transcription factors, the product contains MYB DNA-binding domain and the CC domain. OsPHR2 with transcriptional activation activity and participate in the signal transduction of rice phosphorus starvation conditions.

Function

• OsPHR2 is involved in phosphate-starvation signaling and excessive phosphate accumulation in shoots of plants.Previous research has demonstrated that AtPHR1 plays a central role in phosphate (Pi)-starvation signaling in Arabidopsis thaliana.According to Jie Zhou; FangChang Jiao; Zhongchang Wu;et.al, two OsPHR genes from rice (Oryza sativa) were isolated and designated as OsPHR1 and OsPHR2 based on amino acid sequence homology to AtPHR1. Their functions in Pi signaling in rice were investigated using transgenic plants. Both OsPHR1 and OsPHR2 are involved in Pi-starvation signaling pathway by regulation of the expression of Pi-starvation-induced genes, whereas only OsPHR2 overexpression results in the excessive accumulation of Pi in shoots under Pi-sufficient conditions. Under Pi-sufficient conditions, overexpression of OsPHR2 mimics Pi-starvation stress in rice with enhanced root elongation and proliferated root hair growth, suggesting the involvement of OsPHR2 in Pi-dependent root architecture alteration by both systematic and local pathways. In OsPHR2-overexpression plants, some Pi transporters were up-regulated under Pi-sufficient conditions, which correlates with the strongly increased content of Pi.In OsPHR2-Overexpressing Plants the expression of PSI Genes and PHT Genes altered and OsPHR2 Positively Controls Expression of OsmiR399(figure 1).
• OsPHR2 positively regulates the low-affinity Pi transporter gene OsPT2 by physical interaction and upstream regulation of OsPHO2 in roots. OsPT2 is responsible for most of the OsPHR2-mediated accumulation of excess shoot Pi. OsSPX1 suppresses the regulation on expression of OsPT2 by OsPHR2 and the accumulation of excess shoot Pi, but it does not suppress induction of OsPT2 or the accumulation of excessive shoot Pi in the Ospho2 mutant. OsSPX1 is a negative regulator of OsPHR2 and is involved in the feedback of Pi-signaling network in roots that is defined by OsPHR2 and OsPHO2.. OsPHR2 may control some unknown factors crucial for physiologic utilization of cell Pi.
• Furthermore transgenic rice overexpressing either the Pi transporter OsPht1;8 (OsPT8) or the transcription factor OsPHR2 (for phosphate starvation response2) had enhanced abilities of Pi and arsenate uptake and translocation.

Figure 1. A proposed model for the regulation of low-affinity Pi transporter OsPT2 and the feedback Pi-signaling network defined by OsPHR2, OsSPX1 and OsPHO2 in roots under abundant Pi, and the unknown factor(s) negatively regulating physiologic utilization of cell Pi in shoots under control of OsPHR2.

Expression

• Both OsPHR1 and OsPHR2 showed a similar constitutive expression pattern in all tissues with higher expression level in roots and leaves (Fig. 2A). LikeAtPHR1, the steady expression of OsPHR1 and OsPHR2 in both roots and shoots was not very responsive to Pi deprivation, but the expression of the PSI(Pi-starvation induced) gene OsIPS1 was dramatically induced under Pi-starvation conditions (Fig. 2B). Full-length OsPHR1 and OsPHR2 proteins have transcription activation abilities, and the activation domain of both proteins is located in the N-terminal peptide.

Figure 2. Expression patterns and transcriptional activities of theOsPHR1andOsPHR2genes. A, Tissuespecific expression ofOsPHR1andOsPHR2by RTPCR analysis. B, The expression of OsPHR1and OsPHR2responsive to P starvation. RT-PCR was performed on total RNAs from leaf (L) and root (R) of 21-d-old seedlings after transfer to grow under Pisufficient (1P) and -deficient (2P) conditions for 7 d. The expression ofOsIPS1was tested as a systematic control for the Pi-starvation induction.

Evolution

• OsPHR1(AK063486) and OsPHR2(AK100065)are two homologous genes in rice through a TBLASTN search in the National Center for Biotechnology Information (NCBI) database according to their amino acid sequence identity (SI) to AtPHR1 with 51.7% and 45.5%, respectively. OsPHR1 and OsPHR2 share 43.6% SI with each other. The full-length complementary DNAs (cDNAs) of the two genes were obtained from rice (‘Nipponbare’), followed by PCR amplification using primers predicted from the cDNA sequences. Based on sequencing verification, the obtained cDNAs were identical to the sequence data released from NCBI.OsPHR1andOsPHR2are 1,991- and 1,941-bp long, respectively, and contain an open reading frame (ORF) encoding a predicted protein of 428 and 426 amino acids, respectively. The gene structure analysis showed that both genes have a similar splicing pattern, with the exception of one more exon and intron present in OsPHR2(Fig. 3A).OsPHR1 and OsPHR2 belong to the same subgroup with AtPHR1 and CrPSR1 and are more closely related to AtPHR1 (Fig. 3B).

Figure 3. Structures of the OsPHR1andOsPHR2genes and phylogenetic analysis with other related MYB-CC proteins in Arabidopsis and Chlamydomonas reinhardtii. A, Structures of the OsPHR1andOsPHR2 genes. Exons are indicated as black boxes and introns as white boxes.Numbers indicate the length of each exon and intron. ATG and stop codon are shown with arrowheads. B, Phylogram of proteins sharing the MYB and predicted CC domains constructed using the Clustal(Thompson et al., 1997) program and the neighbor-joining method. The numbers above the lines refer to bootstrap values (of 100 samples). Scale bar, 0.1 substitutions per site.

Labs working on this gene

• Ilse Foissner: Plant Physiology,State Key Laboratory of Plant Physiology and Biochemistry, College of Life Science, Zhejiang University,Hangzhou 310058, China. E-mail: clspwu@zju.edu.cn.
• Front. Biol.:State Key Laboratory of Plant Physiology and Biochemistry, College of Life Sciences, Zhejiang University, Hangzhou 310058, China. E-mail: clspwu@zju.edu.cn.

References

1. Jie Zhou, FangChang Jiao, Zhongchang Wu,at el. OsPHR2 Is Involved in Phosphate-Starvation Signaling and Excessive Phosphate Accumulation in Shoots of Plants. Plant Physiology, 2008, 146(4): 1673-1686.
2. Ping Wu, Zhiye Wang. Molecular mechanisms regulating Pi-signaling and Pi homeostasis under OsPHR2, a central Pi-signaling regulator, in rice. Frontiers in Biology, 2011, 6(3): 242-245.
3. Fang Liu, Zhiye Wang, Hongyan Ren,at el.OsSPX1 suppresses the function of OsPHR2 in the regulation of expression of OsPT2 and phosphate homeostasis in shoots of rice. The Plant Journal, 2010, 62(3): 508-517.
4. Zhongchang Wu, Hongyan Ren, Steve P. McGrath,at el.Investigating the Contribution of the Phosphate Transport Pathway to Arsenic Accumulation in Rice. Plant Physiology, 2011, 157(1): 498-508.