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 (H₂) 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), H₂ pretreatment not only strengthened H₂ 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 H₂-alleviated germination inhibition. The expression of GA biosynthesis genes (GA20ox1 and GA20ox2) and ABA catabolism genes (ABA8ox1 and ABA8ox2), was also induced by H₂. Above results indicated that GA/ABA might be partially involved in H₂ responses. Subsequent results revealed that compared with Al alone, transcripts of miR398a and miR159a were decreased by H₂, 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/OsSTAR2 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 H₂-triggered Al tolerance in plants.