GaRD21A, a cysteine protease gene in Gossypium arboreum is associated with defense response against cotton leaf curl disease

Cysteine proteases (CPs) of the C1-papain family play important roles in plant immunity, particularly in antiviral and antifungal defenses. However, this gene family has not yet been characterized in cotton under Cotton Leaf Curl Disease (CLCuD) stress. Genome-wide diversity analysis and functional annotation revealed the abundance, evolutionary conservation, and conserved peptidase signatures of CP family members across ten Gossypium species and an ancestrally related species Theobroma cacao . Furthermore, a virus-induced gene silencing (VIGS) assay was performed to investigate the role of a papain-like CP gene GaRD21A in resistance response of Gossypium arboreum against CLCuD. Silencing of GaRD21A resulted in increased virus accumulation in both viruliferous whitefly-exposed and graft-mediated CLCuD inoculated plants; however, pronounced vein thickening symptoms were only observed in graft-inoculated plants. To the best of our knowledge, this is the first report demonstrating the involvement of a CP family gene in the immune response of G. arboreum against CLCuD, providing a potential target for cotton resistance breeding programs.