JIA-2018-09

1943 HAN Jiao et al. Journal of Integrative Agriculture 2018, 17(9): 1932–1945 the low-affinity system seems to be constitutive in plants (Raghothama 1999). Plaxton and Carswell (1999) reported that multiple plasmalemma phosphorus transporters differentially exhibit expression under varying phosphorus nutritional regimes. Interestingly, the high-affinity transporter mRNA transcripts in the roots were increased under phosphate deficiency because of an enhanced increase in the root capacities for P uptake (Duncan and Carrow 1999; Shenoy and Kalagudi 2005). These studies suggested that the high-affinity transporters play a critical role in the phosphate acquisition under phosphorus deficiency. In our study, the McPht gene is a typical member of the high- affinity phosphate transport systems, and might be induced at low external phosphate concentration, thereby increasing the relative expression levels of the McPht gene in the transgenic rice comparing to sufficient phosphorus supply. Our data showed that phosphorus deficiency induced the changes of roots architecture and remarkably promoted the roots growth of the transgenic rice, and increased the roots activities and the ratio of the roots to shoots of the transgenic rice although no detailed data were shown. Therefore, we think that the differential expression of the McPht gene seem to be caused by the changes in exudation levels of organic acids from the roots under different levels of phosphorus supply. Zhou et al . (2008) found that the transgenic rice overexpressing the OsPHR2 gene demonstrated an increase in the root length under phosphorus deficiency compared with the wild type. Our data showed that the transgenic rice overexpressing the McPht gene increased the root length and lateral root number in response to phosphorus deficiency than the wild type, and similar result also has been reported (Ren et al . 2014). This study indicated that the overexpression of the McPht gene in the transgenic rice increased the root activities, thus probably promoting the root growth and the root respiration under phosphorus deficiency. Wang et al . (2014) confirmed that the transgenic rice overexpressing the OsPHT1;9 and OsPHT1;10 genes significantly increased the phosphate uptake than the wild type in responses to phosphorus deficiency or excess phosphorus. 4.2. The McPht gene regulates the differentially ex- pressed genes in the secondary metabolites Specific changes in different metabolic pathways and signal transduction pathways were associated with regulatory profiles of the differentially expressed genes under phosphorus deficiency (Marioni et al . 2008; Mortazavi et al . 2008). In our study, the differentially expressed genes are mainly involved in plasmodesma, plasma membrane, cytoplasmic membrane-bounded vesicle, oxidoreductase, transmembrane receptor kinase, the secondary metabolites, sugar metabolism, and the other biological processes. Study showed that differentially expressed genes in maize are mainly involved in sugar synthesis, protein synthesis, amino acid degradation, and the secondary metabolic pathways under phosphorus deficiency (Sun et al . 2016). The up-regulation of genes associated with metabolic pathways contributed to the plant growth, and the differentially expressed genes were related to amino acid metabolism, which supplies a source of C in barley roots under phosphorus deficiency (Carlos et al . 2008; Huang et al . 2008), suggesting that these differentially expressed genes might involve in the metabolism processes of C and N to maintain phosphorus balance in plant cells under phosphorus deficiency. Our results showed that phosphorus deficiency triggered a series of changes in plant secondary metabolic pathways and plant-pathogen interaction. Sun et al . (2016) reported that phosphorus deficiency affected various metabolic pathways, the biosynthesis of the secondary metabolites, and plant-pathogen interactions in maize, and also increased accumulation of anthocyanin in the plants (Zhang et al . 2014). 5. Conclusion The McPht protein is located to the mitochondria, and belongs to a member of the Pht3 subfamily. Phosphorus deficiency induced the expressions of the McPht gene in the M. crystallinum and the transgenic rice, and the overexpression of the McPht gene in the transgenic rice significantly promoted the phosphate uptake and the root development, thus leading to an enhanced increase in the root activities under phosphorus deficiency. Both the up- and down-regulated genes in the transgenic rice are mainly involved in the regulations of molecular function, biological process, and cell component. The enrichments of differentially expressed genes were associated with the up-regulation by participating in the processes of phenylpropanoid synthesis, phenylalanine metabolism, and the secondary metabolite synthesis. This study suggested that the overexpression of the McPht gene in the transgenic rice might participate in an acclimation modulation in the specific up-regulation of differentially expressed genes, and thus promoting the phosphate uptake and physiological metabolism. Acknowledgements This work was supported by the National Key Project for Cultivation of New Varieties of Genetically Modified Organisms, Ministry of Agriculture, China (2016ZX08002- 005), and the National Basic Research Program of China