SUMMARYPhosphate (Pi) transporters mediate acquisition and transportation of Pi within plants. Here, we investigated the functions of OsPht1;4 (OsPT4), one of the 13 members of the Pht1 family in rice. Quantitative realtime RT-PCR analysis revealed strong expression of OsPT4 in roots and embryos, and OsPT4 promoter analysis using reporter genes confirmed these findings. Analysis using rice protoplasts showed that OsPT4 localized to the plasma membrane. OsPT4 complemented a yeast mutant defective in Pi uptake, and also facilitated increased accumulation of Pi in Xenopus oocytes. Further, OsPT4 genetically modified (GM) rice lines were generated by knockout/knockdown or over-expression of OsPT4. Pi concentrations in roots and shoots were significantly lower and higher in knockout/knockdown and over-expressing plants, respectively, compared to wild-type under various Pi regimes. 33 Pi uptake translocation assays corroborated the altered acquisition and mobilization of Pi in OsPT4 GM plants. We also observed effects of altered expression levels of OsPT4 in GM plants on the concentration of Pi, the size of the embryo, and several attributes related to seed development. Overall, our results suggest that OsPT4 encodes a plasma membrane-localized Pi transporter that facilitates acquisition and mobilization of Pi, and also plays an important role in development of the embryo in rice.

SIZ1-mediated SUMOylation regulates hormone signaling as well as abiotic and biotic stress responses in plants. Here, we investigated the expression profile of OsSIZ1 in rice using quantitative reverse transcription-PCR (qRT-PCR) and pOsSIZ1-GUS transgenic plants, and the function of OsSIZ1 in the responses to phosphate and nitrogen using a reverse genetics approach. OsSIZ1 is constitutively expressed throughout the vegetative and reproductive growth of rice, with stronger promoter activities in vascular bundles of culms. ossiz1 mutants had shorter primary roots and adventitious roots than wild-type plants, suggesting that OsSIZ1 is associated with the regulation of root system architecture. Total phosphorus (P) and phosphate (Pi) concentrations in both roots and shoots of ossiz1 mutants were significantly increased irrespective of Pi supply conditions compared with the wild type. Pi concentration in the xylem sap of ossiz1 mutants was significantly higher than that of the wild type under a Pi-sufficient growth regime. Total nitrogen (N) concentrations in the most detected tissues of ossiz1 mutants were significantly increased compared with the wild type. Analysis of mineral contents in ossiz1 mutants indicated that OsSIZ1 functions specifically in Pi and N responses, not those of other nutrients examined, in rice. Further, qRT-PCR analyses revealed that the expression of multiple genes involved in Pi starvation signaling and N transport and assimilation were altered in ossiz1 mutants. Together, these results suggested that OsSIZ1 may act as a regulator of the Pi (N)-dependent responses in rice.

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BackgroundPhosphorus (P), an essential macronutrient, is often limiting in soils and affects plant growth and development. In Arabidopsis thaliana, Low Phosphate Root1 (LPR1) and its close paralog LPR2 encode multicopper oxidases (MCOs). They regulate meristem responses of root system to phosphate (Pi) deficiency. However, the roles of LPR gene family in rice (Oryza sativa) in maintaining Pi homeostasis have not been elucidated as yet.ResultsHere, the identification and expression analysis for the homologs of LPR1/2 in rice were carried out. Five homologs, hereafter referred to as OsLPR1-5, were identified in rice, which are distributed on chromosome1 over a range of 65 kb. Phylogenetic analysis grouped OsLPR1/3/4/5 and OsLPR2 into two distinct sub-clades with OsLPR3 and 5 showing close proximity. Quantitative real-time RT-PCR (qRT-PCR) analysis revealed higher expression levels of OsLPR3-5 and OsLPR2 in root and shoot, respectively. Deficiencies of different nutrients ie, P, nitrogen (N), potassium (K), magnesium (Mg) and iron (Fe) exerted differential and partially overlapping effects on the relative expression levels of the members of OsLPR family. Pi deficiency (−P) triggered significant increases in the relative expression levels of OsLPR3 and 5. Strong induction in the relative expression levels of OsLPR3 and 5 in osphr2 suggested their negative transcriptional regulation by OsPHR2. Further, the expression levels of OsLPR3 and 5 were either attenuated in ossiz1 and ospho2 or augmented in rice overexpressing OsSPX1.ConclusionsThe results from this study provided insights into the evolutionary expansion and a likely functional divergence of OsLPR family with potential roles of OsLPR3 and 5 in the maintenance of Pi homeostasis in rice.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-016-0853-x) contains supplementary material, which is available to authorized users.

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