Stromal Ascorbate Peroxidase ( OsAPX7 ) Modulates Drought Stress Tolerance in Rice ( Oryza sativa ).

Chloroplast ascorbate peroxidases exert an important role in the maintenance of hydrogen peroxide levels in chloroplasts by using ascorbate as the specific electron donor. In this work, we performed a functional study of the stromal APX in rice (OsAPX7) and demonstrated that silencing of OsAPX7 did not impact plant growth, redox state, or photosynthesis parameters. Nevertheless, when subjected to drought stress, silenced plants (APX7i) show a higher capacity to maintain stomata aperture and photosynthesis performance, resulting in a higher tolerance when compared to non-transformed plants. RNA-seq analyses indicate that the silencing of OsAPX7 did not lead to changes in the global expression of genes related to reactive oxygen species metabolism. In addition, the drought-mediated induction of several genes related to the proteasome pathway and the down-regulation of genes related to nitrogen and carotenoid metabolism was impaired in APX7i plants. During drought stress, APX7i showed an up-regulation of genes encoding flavonoid and tyrosine metabolism enzymes and a down-regulation of genes related to phytohormones signal transduction and nicotinate and nicotinamide metabolism. Our results demonstrate that OsAPX7 might be involved in signaling transduction pathways related to drought stress response, contributing to the understanding of the physiological role of chloroplast APX isoforms in rice.