Thylakoidal APX modulates hydrogen peroxide content and stomatal closure in rice (Oryza sativa L.)

In rice (Oryza sativa L.) there are two chloroplast ascorbate peroxidases isoforms, OsAPX7 (stromal) and OsAPX8 (thylakoidal). Previous works demonstrated that double silencing of OsAPX7 and OsAPX8 led to differences in photosynthetic parameters in stress conditions. Nevertheless, both APX encoding genes present contrasting expression patterns in response to abiotic stress and the individual role of them in chloroplast redox metabolism and in stress response remains largely unknown. Here, we showed that plants silenced to OsAPX8 (RNAiOsAPX8) have a lower growth rate and a higher H2O2 content, when compared to non -transformed (NT) plants. Furthermore, RNAiOsAPX8 plants show a decrease in stomatal opening with consequent increase in leaf surface temperature. However, these plants were not more susceptible to drought stress. RNAseq analysis showed that the silencing of OsAPX8 has impact on plant gene expression, mainly affecting genes related to photosynthesis and signal transduction. Our results indicate that the reduction of OsAPX8 expression led to a stress-like phenotype but it does not alter drought tolerance.