Regulation of OsSPX1 and OsSPX3 on Expression of OsSPX domain Genes and Pi‐starvation Signaling in Rice

Abstract

The rice (Oryza sativa L.) genome contains at least six genes exclusively with an SPX (SYG1/PHO81/XPR1) domain at the N-terminal, designated as OsSPX1-6. Here we report the diverse expression patterns of the OsSPX genes in different tissues and their responses to Pi-starvation. Among them, five genes, OsSPX1, 2, 3, 5 and 6 are responsive to Pi-starvation in shoots and/or in roots. The subcellular localization analysis indicates that OsSPX1 and OsSPX2 is exclusively located in nucleus, OsSPX3 in the cytoplasm, and OsSPX4 is a membrane localization protein. OsSPX1 regulates OsSPX2, 3 and 5 at the transcription level and is positively involved in the responses of the genes to Pi-starvation. Overexpression of OsSPX3 downregulates OsSPX5 in shoots under Pi-sufficiency. OsSPX3 negatively regulates the PSI (Pi-starvation induced) gene, OsIPS1 and is involved in the responses of miR399 and OsPHO2 to Pi-starvation. Our results suggest that OsSPX1 may be a regulator involved in the transcriptions of OsSPX2, 3 and 5. OsSPX3 plays a role in OsIPS1/miR399 mediated long distance regulation on OsPHO2. Our results also indicate that OsSPX3 is involved in plant tolerance to Pi-starvation stress.

Spatio-Temporal Transcript Profiling of Rice Roots and Shoots in Response to Phosphate Starvation and Recovery

“…Among the 13 high-affinity Pi transporters encoded by the rice genome, only four have been characterized, namely PT1, PT2, PT6, and PT8 (Ai et al, 2009;Jia et al, 2011;Sun et al, 2012). Similar observations can be made with the SPX gene family where only SPX1 and SPX3 have been characterized (Wang et al, 2009a(Wang et al, , 2009b.…”

“…We measured expression of four known Pi starvationinduced marker genes, namely, the noncoding RNA IPS1 (Hou et al, 2005), the high-affinity Pi transporter PT6 (Ai et al, 2009), SPX2 (Wang et al, 2009b), and MONOGALACTOSYLDIACYL-GLYCEROL SYNTHASE2 (MGD2) involved in galactolipid synthesis (Kobayashi et al, 2009) in roots and shoots ( Figure 1H; see Supplemental Figure 1 online). Expression of these Pi starvationinduced marker genes increased with the duration of Pi deprivation, reaching a maximum after 21 d of Pi starvation, before returning toward basal level after Pi resupply ( Figure 1H).…”

Sugar Signaling in Root Responses to Low Phosphorus Availability

“…Increased expression of AtSPX3 occurs upon prolonged P starvation and appears to act in feedback regulation of plant responses to P starvation by down-regulating the expression of AtSPX1, At4, and genes encoding several Pi transporters, RNases, and phosphatases (Duan et al, 2008). Functional homologs of these genes have been identified in bean (Phaseolus vulgaris; Tian et al, 2007) and rice (Wang et al, 2009a(Wang et al, , 2009bLiu et al, 2010a). In rice, OsSPX1 is induced by low P availability in the roots and acts downstream of OsPHR2 (Wang et al, 2009a).…”

“…In rice, OsSPX1 is induced by low P availability in the roots and acts downstream of OsPHR2 (Wang et al, 2009a). However, OsSPX1 appears to regulate different subsets of P-responsive genes and regulates other members of the OsSPX family in rice differentially between tissues (Wang et al, 2009b). Recently, OsSPX1 has been shown to negatively regulate the expression of OsPHR2 and, consequently, the expression of the rice Pi transporter OsPT2 (Liu et al, 2010a).…”

Rice SPX1 and SPX2 inhibit phosphate starvation responses through interacting with PHR2 in a phosphate-dependent manner

“…In addition, SPX1 and SPX2 are exclusively localized in the nucleus as PHR2, whereas the other SPX proteins are not (14). Genetic analysis indicates that SPX1 has a negative effect on PHR2 (16).…”