3.5 Al-induced differential gene expression of root Pi transporters
The Al-induced expression of Pi transporter and signaling genes in the root tips of XZ29 and XZ9 further confirmed the physiological results (Figure 6). For instance, Al markedly up-regulated HvSPX-MFS2 by 6-fold in XZ29 after 0.5 h and remained higher than control for 6 h. By contrast, expression of HvSPX-MFS2 in XZ9 showed no changes in the first 6 h and decreased to 50% of control levels between 12 and 24 h (Figure 6; Table S8). Moreover, HvPHT1;1 showed a significant increase in expression after 0.5 h in Al treatment, with significantly higher upregulation in XZ29 (22-fold) than in XZ9 (6-fold). The putative mitochondria Pi transporter gene HvPHT3.1 and HvPHT3.2(Hassler et al., 2012) exhibited a rapid increase of expression after 0.5 h Al treatment in both accessions. The expression of HvPHT1;4(Rae et al., 2003) and tonoplast Pi influx gene HvSPX-MFS1 (Liu et al., 2015), the xylem loading Pi transporter gene HvPHO1(Stefanovic et al., 2011) and the Golgi Pi transporter HvPHT4;6(Hassler et al., 2012) were slightly affected by Al (Figure 6).