Molecular And Physiological Mechanism Of OsSULTR3.2 In Regulation Of Phosphate Homeostasis In Rice

Phosphorus is an indispensable element in plant growth and development.The phosphate transporters are responsible for the absorption of phosphate from the soil and the distribution of phosphate among various tissues in the plants.In this article,we reported the function of an uncharacterized member of the sulfate transporters,OsSULTR3.2,in rice(Oryza sativa).The main findings of this research were listed as following: 1.OsSULTR3.2(LOC_Os03g06520)is a member of the sulphate transporter family and the open reading frame(ORF)is 1974 bp length.OsSULTR3.2 encodes a protein with 657 amino acids,which have 10 exons and 9 introns.There are 12 transmembrane domains in the OsSULTR3.2 protein with both N-and C-terminals facing cytosol.There is a STAS(Sulphate Transporter and Anti-sigma Antagonist)domain in its carboxy-terminal.2.OsSULTR3.2 is localized in the endoplasmic reticulum membrane.In normal condition,OsSULTR3.2 was expressed in the root and lateral root,and showed highest expression in the root tips.OsSULTR3.2 was also expressed in lateral root primordium and in the epidermal cells of the root.In addition,OsSULTR3.2 was expressed in mesophyll cells and xylem of vascular bundles in leaves.OsSULTR3.2 was also expressed in the xylem of enlarged vascular bundles at the basal node.3.We determined OsSULTR3.2 expression levels after transfer to phosphate or sulfate deficient conditions by qRT-PCR.The expression of OsSULTR3.2 was significantly inhibited by sulfur deficiency.After 20 days of sulfur starvation,the expression level of OsSULTR3.2 in wild-type(SSBM)roots is reduced by five times.While OsSULTR3.2 was induced by phosphate starvation.The expression level of OsSULTR3.2 in roots increased significantly after exposure to Pi starvation,and the expression level of OsSULTR3.2 increased 6-fold after 20 days phosphate starvation.The increase of OsSULTR3.2 transcript level by Pi starvation was not affected in the phr1 phr2 phr3 triple mutant,suggest that OsPHR1 OsPHR2 OsPHR3 activities were not required for the low-Pi-induced expression of OsSULTR3.2.4.OsSULTR3.2 can catalyze Pi transport across membranes in yeast cells in a low affinity range.5.Under normal sulfate supply conditions,the sulfate concentration in the shoots and roots of the Ossultr3.2 mutant was not significantly different from that of the wild type;analysis of the sulfate concentration in different leaves revealed that the distribution of sulfate in different leaves was not altered in the mutants.Under normal phosphate supply conditions,the Pi concentration in the shoot of Ossultr3.2 was significantly higher than that in the wild type,while phosphate concentration in the roots was not significantly different from the wild type.Compared with the wild type,the phosphate concentration in the old leaves of Ossultr3.2 increased.These results indicate that OsSULTR3.2 was involved in the transport of phosphate in rice.In conclusion,this study revealed that OsSULTR3.2 is localized in the endoplasmic reticulum membrane,and is expressed in the epidermal cells of the root and in xylem of leaves.qRT-PCR results indicated that the expression of OsSULTR3.2 was induced by Pi starvation.Compared with wild-type rice,the Pi concentration in the shoot of Ossultr3.2 was significantly increased,and inorganic phosphorus mainly accumulated in the old leaves.There was no significant difference in the sulfate content of the Ossultr3.2 compared to the wild type.These results further indicate that OsSULTR3.2 functions as a phosphate transporter in rice.