Alleviation of aluminium-induced cell rigidity by overexpression of OsPIN2 in rice roots

Al-induced cell rigidity is one of the symptoms of Al toxicity, but the mechanism by which plants tolerate this toxicity is still unclear. In this study, we found that overexpression of OsPIN2, an auxin transporter gene, could alleviate Al-induced cell rigidity in rice root apices. A freeze-thawing experiment showed that the Al-treated roots of wild-type (WT) plants had more damage in the epidermal and outer cortex cells than that found in lines overexpressing OsPIN2 (OXs), and the freeze-disrupt coefficient was 2-fold higher in the former than in the latter. Furthermore, Al could induce aberrations of the cell wall-plasma membrane interface, which was more prominent in the epidermal cells of the elongation zone of the WT. Overexpressed OsPIN2 reduced Al-induced formation of reactive oxygen species and weakened Al-induced lipid peroxidation and lignification in roots. Compared with WT, a 16.6-32.6% lower Al-triggered hemicellulose 1 accumulation was observed in root apices of OXs, and 17.4-20.5% less Al accumulated in the cell wall of OXs. Furthermore, overexpression of OsPIN2 ameliorated the Al inhibitory effect on basipetal auxin transport and increased Al-induced IAA and proton release. Taken together, our results suggest that by decreasing the binding of Al to the cell wall and Al-targeted oxidative cellular damage, OXs lines show less Al-induced damage. By modulating PIN2-based auxin transport, IAA efflux, and cell wall acidification, lines overexpressing OsPIN2 alleviate Al-induced cell rigidity in the rice root apex.