Mannose-binding lectin 1.1A interacts with hypersensitive-induced response 4 to promote hypersensitive cell death and defense responses in cotton upon Verticillium dahliae infection.

Increasing evidence indicates that mannose-binding lectins (MBLs) act as a lectin-receptor-like protein in plant immune responses, yet the functional basis remains elusive. In this study, we dissected the functional mechanism of GbMBL1.1A in defense against Verticillium dahliae infection in sea island cotton (Gossypium barbadense). GbMBL1.1A expressed preferentially in cotton roots and significantly upregulated upon V. dahliae infection. Transgenic expression of GbMBL1.1A in upland cotton (Gossypium hirsutum) and Arabidopsis remarkably improved the disease resistance of the plants, while silencing of GbMBL1.1A resulted in an increased susceptibility of cotton plants in response to V. dahliae attack. Protein interaction assays revealed that GbMBL1.1A interacted with the cotton hypersensitive-induced response protein 4 (GbHIR4, a scaffold protein for immune signaling in the plasma membrane microdomain) through PAN domain. GbHIR4 expression was upregulated in response to V. dahliae invasion, and silencing of GbHIR4 seriously attenuated the disease tolerance of cotton plants. GbMBL1.1A enhanced the cell death phenotype induced by the transient expression of GbHIR4, and meanwhile promoted HR-PCD and GbHIR4-dependent resistance upon V. dahliae infection. The results suggested that GbMBL1.1A employed GbHIR4 as a downstream component to trigger the hypersensitive responses and therefore contributed to cotton resistance against V. dahliae. In addition, we observed that GbMBL1.1A overexpression could alter the phytohormone-mediated defense and growth signaling under both normal and V. dahliae infection conditions. Collectively, these results demonstrated that the lectin receptor-like protein GbMBL1.1A interacts with GbHIR4 in cotton immunity to induce the hypersensitive response, which is associated with phytohormone-mediated defense and growth signaling.