Ascorbate Alleviates Fe Deficiency-Induced Stress in Cotton (Gossypium hirsutum) by Modulating ABA Levels

Abstract

Fe deficiency causes significant losses to crop productivity and quality. To understand better the mechanisms of plant responses to Fe deficiency, we used an in vitro cotton ovule culture system. We found that Fe deficiency suppressed the development of ovules and fibers, and led to tissue browning. RNA-seq analysis showed that the myo-inositol and galacturonic acid pathways were activated and cytosolic APX (ascorbate peroxidase) was suppressed in Fe-deficient treated fibers, which increased ASC (ascorbate) concentrations to prevent tissue browning. Suppression of cytosolic APX by RNAi in cotton increased ASC contents and delayed tissue browning by maintaining ferric reduction activity under Fe-deficient conditions. 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. Abscisic acid (ABA) levels were significantly decreased in Fe-deficient treated ovules and fibers, while the upregulated expression of ABA biosynthesis genes and suppression of ABA degradation genes in Fe-deficient ovules slowed down the decreased of ABA in cytosolic APX suppressed lines to delay the tissue browning. Moreover, the application of ABA in Fe-deficient medium suppressed the development of tissue browning and completely restored the ferric reduction activity. In addition, ABA 8′-hydroxylase gene (GhABAH1) overexpressed cotton has a decreased level of ABA and shows more sensitivity to Fe deficiency. Based on the results, we speculate that ASC could improve the tolerance to Fe deficiency through activating Fe uptake and maintaining ABA levels in cotton ovules and fibers, which in turn reduces symptom formation.

Regulation of Ascorbate-Glutathione Pathway in Mitigating Oxidative Damage in Plants under Abiotic Stress

“…All of the APX isoforms are heme peroxidase they are inhibited by cyanide and azide. Iron plays a vital role in the APX catalytic site; hence, despite the presence of high AsA concentration, Fe deficiency reduced the activity of cAPX [42]. If the single Cys32 residue near arginine (Arg) 172 residue is altered, APX loses the ability to oxidize AsA to DHA, but it can oxidize other small aromatic molecules.…”

Expression of the Arabidopsis Mg-chelatase H subunit alleviates iron deficiency-induced stress in transgenic rice

“…Fe deficiency induces chlorosis in young leaves, which causes severe reductions in yield and grain quality at the adult stage (Guo et al, 2017;Kobayashi et al, 2019). Here, we present a new approach to ameliorate Fe deficiency-induced stress of plants through manipulation of porphyrin biosynthesis.…”

“…While ABA participates in Fe homeostasis and alleviation of Fe deficiency (Lei et al, 2014;Guo et al, 2017;Zhang et al, 2020), its exact role in Fe homeostasis remains unknown. Since exogenous application of ABA did not rescue Fe deficiency phenotypes including the chlorosis and growth defects of WT and transgenic seedlings observed upon Fe deficiency (Figures 8A, B), AtCHLH is unlikely to affect Fe deficiency responses via ABA signaling.…”

Cytosolic Ascorbate Peroxidases Plays a Critical Role in Photosynthesis by Modulating Reactive Oxygen Species Level in Stomatal Guard Cell

“…In our previous researches, we found that the suppression of cAPXs increased tolerance to Fe deficiency by modulating ABA level in cotton, and the specific suppression of GhAPX1 was unable to alter the response of cotton to Fe deficiency (Guo et al, 2016b). Moreover, cAPX-suppressed cotton fibers showed more sensitivity to oxidative stress than did wild-type plants, and the overexpression of GhAPX1 improved the tolerance of fibers to oxidative stress in cotton (Guo et al, 2016a).…”

“…Samples (0.07 g) were extracted in a 10-ml tube with 6 ml of 80% ethanol, heated to 80 • C for 30 min, and then centrifuged at 12,000 × g for 15 min. The supernatant was used for the assay of glucose, fructose, and sucrose according to a previous method (Guo et al, 2016b).…”