Table 1.
species | gene | protein location | expression after Pi starvation | regulation of PSI gene | main functional characteristics | source |
---|---|---|---|---|---|---|
Oryza sativa | OsSPX1 | N | + | Nr | OsSPX1 can interact with OsPHR2 and acts as a negative regulator of OsPHR2. OsSPX1 regulates OsSPX2, 3 and 5 at the transcriptional level, and the repression of OsSPX1 results in excessive P accumulation in the shoot | Wang et al. [27,28] |
OsSPX2 | N | + | OsSPX2 can interact with OsPHR2 and acts as a negative regulator of OsPHR2. PHR2, SPX1 and SPX2 constitute a regulatory feedback loop in P signalling | Wang et al. [28,45] | ||
OsSPX3 | N/C | + | Nr | OsSPX3 plays an important role in OsIPS1/miR399-mediated long distance regulation on OsPHO2 and acts as a negative regulator of OsPHR2. OsSPX3 negatively regulates the root-to-shoot transportation of P. Overexpression of OsSPX3 inhibits plant growth, which is more severe under P-deficient conditions | Wang et al. [28] Shi et al. [46] |
|
OsSPX4 | N/C | = | OsSPX4 can interact with OsPHR2 in the cytoplasm and inhibits translocation of PHR2 into the nucleus. OsSPX4 functions as a negative regulator of PHR2 and can affect the activity of OsPHR2, sequentially regulating downstream gene expression | Lv et al. [47] | ||
OsSPX5 | N/C | + | Nr | OsSPX5 and OsSPX3 are paralogous genes. SPX3/5 proteins act as repressors of PHR2. Overexpression of SPX3 and SPX5 completely rescues the excessive shoot of P accumulation. SPX3/5 negatively regulates P transport from roots to leaves with redundant function | Shi et al. [46] Zhang et al. [43] |
|
OsSPX6 | + | OsSPX6, as a paralogue of SPX3/5, may play a compensatory role | Shi et al. [46] | |||
Arabidopsis thaliana | AtSPX1 | N | + | Pr | AtSPX1 can interact with AtPHR1 and may act as a negative regulator of AtPHR1 in P concentration | Duan et al. [26] Qi et al. [48] |
AtSPX2 | N | + | AtSPX2 can interact with AtPHR1 in the cell nucleus. AtSPX1 and AtSPX2 have functional redundancy with one another | Puga et al. [49] | ||
AtSPX3 | M/C | + | Nr | Partial repression of AtSPX3 can exacerbate phosphate-deficiency symptoms, alter P allocation and enhance the expression of a subset of phosphate starvation responsive genes including AtSPX1 | Duan et al. [26] | |
AtSPX4 | M | − | AtSPX4 can interact with AtPHR1 in the cytoplasm | Duan et al. [26] | ||
Glycine max | GmSPX1 | N/C | +(*) | Nr | GmSPX1 interacts with a newly identified P starvation-induced transcription factor GmMYB48, and this interaction may represent a potential suppressor of P signalling network in soya bean | Zhang et al. [43] |
GmSPX2, 4, 6, 9 and 10 | N/C | + | — | Yao et al. [50] | ||
GmSPX3, 7 and 8 | N | + | GmSPX3 overexpression results in increased P concentration in both leaf and root tissues under high P conditions, which correlates with elevated transcript levels of several PSI genes in the root hairs | Yao et al. [50] | ||
GmSPX5 | N/C | +(**) | — | Yao et al. [50] | ||
Phaseolus vulgaris | PvSPX1 | N | + | Pr* | Overexpression of PvSPX1 results in increased P concentration in the roots, morphological change in root hairs, inhibition of main root growth, more numerous lateral roots and upregulated transcription of 10 PSR genes | Yao et al. [44] |
PvSPX2 | N | + | Pr* | PvSPX2 participates in P signalling pathway in both shoot and root tissues. Overexpression of PvSPX2 results in increased transcription of several genes downstream from PvSPX1, suggesting that PvSPX2 might have a similar regulatory role as PvSPX1 | Yao et al. [44] | |
PvSPX3 | N/C | + | = | PvSPX2 participates in P signalling pathway in both shoot and root tissues. PvSPX3 expression is less sensitive to P deficiency compared with that of PvSPX1 and PvSPX2 | Yao et al. [44] | |
Triticum aestivum | TaSPX129 | + | — | Fang et al. [51] | ||
TaSPX | TaSPX participates in high temperature-induced resistance to wheat stripe rust | Wei et al. [52] |