GhCPK28 negatively regulates the immune response by phosphorylating GhTIFY3b

The soil-borne fungus Verticillium dahliae (V. dahliae) seriously inhibits cotton (Gossypium hirsutum) growth and productivity. The immune system of cotton against this pathogen is largely unknown. Here we investigated the involvement of Ca2+-dependent protein kinases (CPKs) in this immunity. One CPK coding gene GhCPK28 had reduced expression after infection by V. dahliae in cotton. Knocking down of the GhCPK28 by virus induced gene silencing led to enhanced resistance to V. dahliae which is accompanied by a higher ROS accumulation and systemic acquired response. GhCPK28 was found to phosphorylate a TIFY family protein GhTIFY3b and reduce its stability. Silencing GhTIFY3b increased the susceptibility of cotton to V. dahliae. Together, this study indicate that GhCPK28 is a negative regulator of defense against V. dahliae infection and the GhTIFY3b might be a target protein of its activity. It sheds light on the immune system against V. dahliae and provides candidate genes for improving resistance against Verticillium wilt in cotton.