Isolation of high-affinity phosphate transporters SbPT1 AND SbPT2 in Sorghum bicolor and their characterization in contrasting genotypes
Phosphate (Pi) availability is highly limited in the acidic soils of the Brazilian savannahs (Cerrado) used for sorghum cultivation. Although several sorghum genotypes contrasting for P use-efficiency have been developed from natural genetic variants, the Pi transport pathway mechanisms in these plants remain unclear. High-affinity Pi transporters play a pivotal role in Pi acquisition by roots and its subsequent mobilization to aerial parts of the plant. We investigated the potential roles of high-affinity Pi transporters in Pi use efficiency in contrasting genotypes of sorghum. A cDNA library prepared from Pi-deprived sorghum seedlings was screened with heterologous Zea mays (maize) Pi transporters ZmPTs, leading to isolation of two homologous sorghum genes referred to as SbPT 1 and SbPT2. Southern analysis revealed that a small gene family represents the SbPTs genes in the sorghum genome. There were significant increases in the transcription levels of SbPT1 and SbPT2 in roots of Pi-deprived seedlings of both Pi-use efficient (101B) and Pi-use inefficient (136B) genotypes. A decrease in the transcript levels of these transporters in 101B and 136B upon Pi replenishment suggested their transcriptional regulation by Pi. Although SbPT1 and SbPT2 were induced in the roots, and in young and old leaves of Pi-deprived sorghum, high transcription levels were observed exclusively in the stems of Pi-efficient genotype 101B under Pi-deprivation. This suggests a role of SbPTs in the efficient mobilization of Pi from the root to the shoot, which could be one of the factors conferring higher Pi-use efficiency in this genotype.