A cotton APS REDUCTASE represses root hair elongation via sulfur assimilation and hydrogen peroxide-mediated cell wall damage

Sulfur is a critical element for plant growth and development, and it is assimilated through a pathway called the sulfur assimilation pathway. APS REDUCTASE (APR) is a key rate-limiting enzyme in this pathway, and it plays a vital role in regulating sulfur flow and plant development. However, the exact role and mechanism of APR in cotton fiber and root hair development are still not fully understood. This study used in vitro cultured ovules grown on a sulfur-deficient medium to explore the role of sulfur in fiber development. Genetic approaches such as virus-induced gene silencing (VIGS) was used to determine the role of target genes. In vitro assays revealed the role of sulfur in fiber development and identified GhAPR2 as a key candidate gene. The GhAPR2 negatively regulates fiber cell initiation and Arabidopsis root hair elongation. Further studies demonstrated that overexpression of GhAPR2 increased the contents of sulfite and GSH to enhance sulfur assimilation in Arabidopsis, leading to abnormal accumulation of ROS in root hair. This down-regulates the transcription of proline-rich cell wall protein-coding genes such as AtEXTs and AtPRPs, reducing the content of hydroxyproline in the cell wall, disrupting the development of the root hair cell wall, and inhibiting root hair elongation. This study elucidated the functional pathway of APR2 in the regulation of root hair development. APR2 first affects sulfur assimilation, which affects the content of reactive oxygen species (ROS), and finally affects the content of hydroxyproline-rich glycoprotein, which in turn affects the development of root hair. This model also contributes to the understanding of the role of sulfur in fiber development, as well as cell differentiation and development.