JIA-2018-09

1933 HAN Jiao et al. Journal of Integrative Agriculture 2018, 17(9): 1932–1945 1. Introduction Phosphorus (Pi) nutrition is essential for plant growth and development, and widely involved in the physiological- biochemical metabolic processes (Richardson 2009). As an important component of nucleic acids and phospholipids, phosphate plays important regulatory roles in the photosynthesis, energy metabolism, signal transduction, gene expressions, and enzymatic reactions (Yang and Finnegan 2010). The phosphate uptake by plants depends on the amounts of available phosphate, which is usually present in the forms of HPO 4 2– and H 2 PO 4 – , and phosphate availability is relatively limited in soils although the phosphate contents exceed 40 mmol L –1 in plants (Bollons and Barraclough 1997), thus indicating that the phosphate uptake by plant is an inverse process accompanying concentration gradient energy dissipation. Therefore, the establishment of an adaptive mechanism for improving phosphate uptake efficiency (PUE) is necessary by altering root morphology and accumulation of anthocyanins under phosphorus deficiency (Raghothama 1999). The uptake and transport of phosphate in plants are mainly participated by the high-affinity phosphate transporter and the low-affinity phosphate transporter (Christine et al . 2002). Currently, the phosphate transporters are divided into the Pht1, Pht2, Pht3, and Pht4 subfamilies (Lin et al . 2009). The Pht1 subfamily is composed of a cluster of high affinity phosphate transporters, which contain 12 transmembrane regions with the N- and C-terminal ends mounting inside of cell (Raghothama 1999; Bucher et al . 2001; Christine et al . 2002). Many Pht1 subfamily members have been functionally profiled in tomato (Xu et al . 2007), Arabidopsis (Nagarajan et al . 2011), and rice (Ai et al . 2009). Total 13 of phosphate transporters in rice were confirmed to be the Pht1 subfamily (Christine et al . 2002). Both the Pht1;1 and Pht1;4 are highly expressed in the roots of Arabidopsis under phosphorus deficiency (Shin et al . 2004). The transgenic rice overexpressing OsPht1;4 revealed higher Pi concentrations in the roots and shoots under different phosphate levels compared with the wild type (Zhang et al . 2015). Similar to the Pht1, the Pht2 subfamily members also posses 12 transmembrane regions with a central hydrophilic loop in the middle at the 8th and 9th regions (Daram et al . 1999), but most of the Pht2 subfamily members have been identified to function as low-affinity phosphate transporters such as AtPht2;1 (Daram et al . 1999), MtPht2;1 (Zhao et al . 2003), and TaPHT2;1 (Guo et al . 2013). Study showed that the PHT2;1 affected the phosphate accumulation and gene expression in the leaves under phosphorus deficiency (Versaw and Harrison 2002). The expression of the MtPHT 2;1 gene in leaves was confirmed to be closely related to the supply levels of phosphate and located to the chloroplast envelope (Zhao et al . 2003). Unlike the Pht1 and Pht2, the Pht3 subfamily members belong to the high-affinity phosphate transporters which are composed of six transmembrane domains, and have been functionally characterized in soybean, maize, rice, and Arabidopsis (Takabatake et al . 1999). Stappen and Kramer (1994) reported that the Pht3 subfamily functions in promoting the phosphate exchange through the co-transport of Pi/H + and the reverse transport of Pi/OH – in cells. The mitochondrial phosphate transporter (MPT) gene in Arabidopsis has been identified. More accumulation of the AtMPT mRNA led to higher ATP contents in the transgenic Arabidopsis , and a large number of genes is related to gibberellin synthesis and regulated by changing available energy under salt stress (Zhu et al . 2012). Like the Pht3, the Pht4 subfamily members are also composed of 6 transmembrane regions, but most of them were functionally identified in Arabidopsis . The PHT4 gene was mainly expressed in the leaves and roots of Arabidopsis thaliana , and confirmed to be located to the plastid envelope or the Golgi apparatus (Guo et al . 2008). Rice is one of the most important food crops, and has been used as model for gene functional analyses. In this study, the McPht gene, a mitochondrial phosphate transporter, was isolated from Mesembryanthemum crystallinum , which has an ecological adaptation to high saline soils or infertile soils or desert soils (Adams et al . 1998), thus showing that M. crystallinum reveals stronger adaptive mechanism to phosphorus deficiency and phosphate transporters might play crucial regulatory roles in the uptake of limited available phosphate in poor soils. To date, no detailed study on mitochondrial phosphate transporter from M. crystallinum was reported (Winter and Holtum 2007). Therefore, we constructed a plant transformation vector carrying the McPht gene and 35S promoter, and transferred this construct into rice cv. Kitaake ( Oryza sativa japonica L.), and three T 2 generations of the transgenic rice lines with stable hereditary were selected. interaction. These results indicated that the overexpression of the McPht gene might participate in the physiological adaptive modulation of the transgenic rice to phosphorus deficiency by up- or down-regulating the differentially expressed genes. Keywords: McPht gene, phosphorus deficiency, phosphate transporter, transcriptome sequencing, transgenic rice