Linking hydrogen-enhanced rice aluminum tolerance with the reestablishment of GA/ABA balance and miRNA-modulated gene expression: A case study on germination

Although previous results showed that exogenous hydrogen (H-2) alleviated aluminum (Al) toxicity, the detailed mechanism remains unclear. Here, we reported that the exposure of germinating rice seeds to Al triggered H2 production, followed by a decrease of GA/ABA ratio and seed germination inhibition. Compared to inert gas (argon), H-2 pretreatment not only strengthened H-2 production and alleviated Al-induced germination inhibition, but also partially reestablished the balance between GA and ABA. By contrast, a GA biosynthesis inhibitor paclobutrazol (PAC) could block the H-2-alleviated germination inhibition. The expression of GA biosynthesis genes (GA20oxl and GA20ox2) and ABA catabolism genes (A13A8ox1 and ABA8ox2), was also induced by H-2. Above results indicated that GA/ABA might be partially involved in H-2 responses. Subsequent results revealed that compared with Al alone, transcripts of miR398a and miR159a were decreased by H-2, and expression levels of their target genes OsSOD2 and OsGAMYB were up-regulated. Whereas, miR528 and miR160a transcripts were increased differentially, and contrasting tendencies were observed in the changes of their target genes (OsAO and OsARF10). The transcripts of Al-tolerant gene OsSTAR1/0sSTAR2 and OsFRDL4 were up-regulated. Above results were consistent with the anti-oxidant defense, decreased Al accumulation, and enhanced citrate efflux. Together, our results provided insight into the mechanism underlying H-2-triggered Al tolerance in plants.