title: Does OsPHR2, central pi-signaling regulator, regulate some unknown factors crucial for plant growth?
abstract: OsPHR2, the homolog of AtPHR1, is a central Pi-signaling regulator. The Pi-signaling pathway downstream of AtPHR1, similarly of OsPHR2,1,2 involves a noncoding RNA which targets mimicry of miR399. miRNA399 mediates cleavage of PHO2. (3,4) The regulating pathway downstream of OsPHR2 is negatively regulated by the Pi-signaling responsive gene OsSPX1. (5,6) Overexpression of AtPHR1 and OsPHR2 leads to an increased concentration of Pi in the shoot tissues with leaf toxic symptom and growth retardation similar as the phenotype of pho2 mutant, especially under Pi abundant conditions. (7,2,6) It has been known that the low affinity Pi transporter OsPT2 mainly contributes to the shoot Pi accumulation mediated by OsPHR2, and overexpression of OsPT2 results in shoot Pi accumulation and leaf toxic symptom and growth retardation under Pi abundant conditions. (6) Two curious questions are emerging from the reported results: How Os SPX1 functions on the negative regulation of the pathway and what mechanism of the growth retardation mediated by OsPHR2. For the second question, our favored hypothesis is that the growth inhibition mediated by overexpression of OsPHR2 is caused by toxic physiological effects due to excessive Pi accumulation in shoots (Pi toxicity). In fact, the toxic symptoms become diminished with decreased Pi levels in growth medium. However, the plant growth retardation mediated by overexpression of OsPHR2 may be caused by some unknown genetic factor(s) regulated by OsPHR2.
authors.affiliation: State Key Laboratory of Plant Physiology and Biochemistry, College of Life Science, Zhejiang University, Hangzhou, China. clspwu@zju.edu.cn
authors.forename: Ping
authors.initials: P
authors.lastname: Wu
authors.forename: Jiming
authors.initials: J
authors.lastname: Xu
references.citation: Plant Physiol. 2004 May;135(1):400-11
references.pmid: 15122012
references.citation: Plant Physiol. 1991 Nov;97(3):1087-93
references.pmid: 16668493
references.citation: Plant J. 2008 Jun;54(6):965-75
references.pmid: 18315545
references.citation: Plant J. 2010 May;62(3):508-17
references.pmid: 20149131
references.citation: Nat Genet. 2007 Aug;39(8):1033-7
references.pmid: 17643101
references.citation: Plant Cell. 2002 Apr;14(4):889-902
references.pmid: 11971143
references.citation: Genes Dev. 2001 Aug 15;15(16):2122-33
references.pmid: 11511543
references.citation: Plant Physiol. 2008 Apr;146(4):1673-86
references.pmid: 18263782
references.citation: Plant Cell Physiol. 1993 Apr;34(3):401-10
references.pmid: 8019781
references.citation: Plant J. 2009 Mar;57(5):895-904
references.pmid: 19000161
references.citation: Annu Rev Plant Biol. 2007;58:47-69
references.pmid: 17067284
references.citation: J Integr Plant Biol. 2009 Jul;51(7):663-74
references.pmid: 19566645
references.citation: Plant Cell Environ. 2007 Dec;30(12):1499-512
references.pmid: 17927693