Function Analysis Of OsLIR1on Carbon And Phosphorus Homeostasis Of Rice

Plant nutrition status is subject to endogenous circadian rhythm. By the comparative analysis of transcription profiles in rice transgenic plants with overexpression and repression of OsPHR2(the Pi-signaling regulator), we isolated a gene OsLIR1under the regulation of OsPHR2. Bioinformatics analysis showed that OsLIR1is a circadian rhythm gene, Study of the function of OsLIR1using the transgenic plants with overexpression and repression of OsLIR1provide the following conclusions:1. Rice OsLIR1is a circadian gene which accumulates in the light and reaching maximum and minimum steady-state levels at the end of the light and dark period respectively. The transcript level of OsLIR1is much higher in leaves than that in roots and its expression is down regulated by Pi-starvation especially in roots.2. The transient expression of GFP fused OsLIR1in onion epidermal cells and tobacco leaf cells indicate that OsLIR1protein is located in plastid and chloroplast. The transgenic plants harboring GUS report gene drive by OsLIR1promoter showed that OsLIR1is expressed in root tip, root cortical cells, stem cortical cells, leaf mesophyll cells and glumes.3. The transgenic plants with overexpression of OsLIR1driven by CaMV35S promoter (OsLIR1(O)) and repression of OsLIR1through RNAi interfering(OsLIR1(RI)) were developed. Both OsLIR1(O) and OsLIRl (RI) showed stunted growth, reduced pollen viability, decreased seed setting rate and necrosis of the leaf tips.4. Both of Transgenic lines OsLIR1(O) and OsLIR1(RI) have significantly increased phosphate concentration in roots and leaves. QRT-PCR analysis indicated that the expression of the phosphate transporters OsPT2, OsPT6, OsPT8and OsPT9were up-regulated in the transgenic plants, the expression patterns of the phosphate-starvation responsive genes OsSQD2, OsPAPIO, OsIPS1and OsPH02were not significantly changed except the OsmiR399d which was down-regulated in the transgenic plants with both overexpressed and repressed OsLIR1plants.5. The analysis of the starch and sucrose concentration in the OsLIRl (O) and OsLIR1(RI) indicated that the starch and sucrose are high accumulated in roots and leaves in the transgenic plants at morning. The results suggest that OsLIRl may participate in the regulation of the transient starch degradation in the night.6. To investigate the effect of OsLIRl in the rice circadian clock network, we analyzed the expression patterns of OsCCA1, OsTOC1and OsPCL1. The OsLIR1(O) and OsLIRl (RI) causes a significant amplitude decrease in expression of the evening gene OsTOC1and OsPCL1, but little effect on the morning gene OsCCAl. This indicates that OsLIR1may be involved in the regulation of the evening loop of the circadian clock network.OsLIR1is a light-dependent circadian gene, it’s involved in the carbon and phosphorus homeostasis of plant. Study the gene’s function will elucidate the relationship between the circadian rhythm and carbon-phosphorus homeostasis.