Identification and characterization of phosphate transporter genes in potato

Phosphate transporter (PHTs) have important roles in Pi acquisition, allocation, and signal transduction. The aim of this study is to provide a comprehensive knowledge of PHTs in potato. Very strict homology search and subsequent domain verification using Hidden Markov Models revealed that the potato genome has 20 StPHT and StPHOs genes which were grouped into 5 phylogenetical clusters including 8 PHT1 homologs, 1 PHT2 homolog, 2 PHT3 homologs, 5 PHT4 homologs and 4 PHO homologs. These genes were mapped on ten S. tuberosum chromosomes (chr1-9 and 12). Analysis of these genes led to identification of 20 conserved motifs and location prediction showed that PHT1 and PHT4 proteins have 12 transmembrane (TM) domains, PHT2 proteins have 13 TM domains, PHT3 proteins contain 4-5 TM domains, and PHO proteins contain 8-10 TM domains. Two tandem and 2 segmental duplications were further identified from these genes. RT-qPCR analysis showed that most of PHTs and PHOs displayed specific expression patterns with respect to phosphate status, fourteen transporters were up regulated in leaves and 11 transporters were up regulated in roots under phosphate deprivation. StPHT2; 1 was found to be expressed both in potato leaf and root after phosphate starvation. Most cis-regulatory elements in StPHTs and StPHOs were found associated with light, defense, stress and hormones responsiveness, endosperm and meristem expression, as well as circadian control. A scan of the coding sequences of 20 StPHTs and StPHOs against published miRNAs in potato predicted a total of 2 potential miRNAs, mainly targeting members located on the same chromosome. Expression of StPHTs and StPHOs was selectively induced by biotic and abiotic stresses, and phytohormone treatments, among them, heat stress exclusively caused the up-regulation of 14 StPHT and StPHO genes, in particular PHO1 members. Most of StPHTs and StPHOs do not exhibit the tissue-specific expression. StPHT1;7, StPHT3;1 and StPHTO1;1 were highly expressed in the root of S. tuberosum, especially the gene StPHT3;1 are highly expressed in 14 tissues which covering the entire life cycle of potato. Our results provide comprehensive insights into the PHT and PHO family genes involved in the growth, development, and stress response of the potato.