Silencing of GhGRL28 in cotton increases sensitivity to salt stress

Glutaredoxin-like (GRL) belongs to the glutaredoxin (GRX) protein family that plays an important role in the growth, development and antioxidant response of many organisms. However, little information is available for GRL genes in cotton ( Gossypium hirsutum ). This study aims to identify genome-widely GRL genes in Gossypium hirsutum and G. barbadense as well as their diploid ancestors G. arboreum and G. raimondii to explore their function in salt tolerance. Based on the expression change of GhGRL genes in response to salt stress, GhGRL28 was found to be significantly induced by salt stress and was selected for functional characterization by knocking down the gene using virus-induced gene silencing. Compared with the control plants, the GhGRL28 silenced plants grew more slowly and were more sensitive to salt stress, showing obviously withered and yellowed leaves, inhibited root development, decreased stomatal aperture and increased stomatal density. Consistent with the phenotypic changes, the GhGRL28 silenced plants had a higher content of H 2 O 2 and O 2 − than the control plants under the salt stress conditions, likely due to compromised activation of the enzymes, such as superoxide dismutase (SOD) and peroxidase (POD), involved in ROS scavenging. After salt treatment, compared to the control plants, the GhGRL28 silenced plants had a weaker transcription activity of glutathione ( GSH ) gene, a lower GSH/oxidized glutathione (GSSH) ratio and a higher (increased by 24.77%) MDA content, indicating a severer degree of membrane lipid peroxidation in the GhGRL28 silenced plants. These results imply that GhGRL28 is actively involved in the regulation of redox species induced by stresses and is important for maintaining the growth and development of cotton plants under stress conditions.