Ascorbate regulates cotton fiber development

GhAPX1AT/DT (Ascorbate peroxidase) encoded one member of the previously unrealized group of cytosolic APXs (cAPXs) that were preferentially expressed during the fiber elongation stage. Suppression of all cAPX (IAO) resulted in a 3.5-fold increase in H2O2 level in fiber and oxidative stress, and significantly suppressed fiber elongation. The fiber of over-expression lines exhibited higher tolerance to oxidative stress. Differentially expressed genes (DEGs, by RNA-seq) in 10 DPA fiber of IAO lines were related to redox homeostasis, signaling pathways, stress responses and cell wall synthesis, and the DEGs that were up-regulated in IAO lines were also up-regulated in the 10 DPA and 20 DPA wild cotton fiber compared with domesticated cotton. These results suggest that optimal redox state regulated by cytosolic APX are key mechanisms regulating fiber elongation. Furthermore, suppression of cAPX increased ASC contents and delayed tissue browning by maintaining ferric reduction activity under Fe-deficient conditions in the ovule culture system. Meanwhile, APX RNAi line also exhibited the activation of expression of iron-regulated transporter (IRT1) and ferric reductase–oxidase2 (FRO2) to adapt to Fe deficiency.