Flagellin FLiC Enhances Resistance of Upland Cotton to Verticillium dahliae

The mechanism by which flagellin induces an immune response in plants is still unclear. The purpose of this study is to reveal the effect and mechanism of flagellin in inducing plants to produce an immune response to increase the resistance to Verticillium dahliae (VD). The full-length flagellin gene C (FliC) was cloned from an endophytic bacteria (Pseudomonas) in the root of upland cotton cultivar Zhongmiansuo 41. The FliC protein purified in vitro has 47.50% and 32.42% biocontrol effects on resistant and susceptible cotton cultivars, respectively. FLiC can induce allergic reactions in tobacco leaf cells and immune responses in cotton plants. Smearing FLiC to cotton and performing RNA-seq analysis, it is significantly enriched in the activity of positive ion transporters such as potassium ions and calcium ions (Ca2+), diterpenoid biosynthesis, phenylpropane biosynthesis and other disease-resistant metabolic pathways. FLiC inhibits the expression of calcium antiporter activity gene (GhCAA) to accelerate intracellular Ca2+ influx and stimulate the increase of intracellular hydrogen peroxide (H2O2) and nitric oxide (NO) content. The coordinated regulation of Ca2+, H2O2 and NO enhances disease resistance. The resistance of transgenic FLiC gene Arabidopsis to VD was significantly improved. The FLiC gene can be used as an anti-VD gene and as a regulator to improve resistance to VD.