The GhHSP90-7 and GhHSP70-8 augment cotton fiber development by regulating reactive oxygen species (ROS) response

Being a longest unicellular structure, cotton fiber is the most suitable platform for studying cellular differentiation, development, and cell wall biosynthesis in the plant system. A range of transcription factors, hormones, epigenetic factors and H₂O₂ play essential role in fiber development. Our previous work reported an accumulation of high H₂O₂ levels on the epidermis of in-vitro cultured ovules treated with the inhibitors of HSP90 and HSP70, which lead to autophagy and ultimately declined fiber initials. In this study, we investigated the susceptibility of cotton fiber development to cellular ROS imbalance due to altered GhHSP90-7 and GhHSP70-8 expression in transgenic cotton lines. The expression analysis reflected the highest expression of GhHSP90-7 and GhHSP70-8 at 0 Days post anthesis (DPA) in comparison to later developmental stages suggesting their importance in fiber initiation. Suppression and over-expression lines of these Heat Shock Proteins (HSPs) showed the decreased fiber growth in initiation and elongation stages. Almost all fiber-related traits got impacted in all HSP transgenic lines. Further, ROS levels were found imbalanced in transgenic ovules due to alteration in HSPs expression, leading to the disruption of cellular homeostasis. High ROS accumulation in suppression lines lead to autophagy in ovule epidermal cells. Low ROS concentrations also affected fiber initiation as ROS molecules act as signaling molecule and so the expression of fiber initiation specific transcription factors found to be declined significantly. These results show the GhHSP90-7 and GhHSP70-8 play important role in cotton fiber development.