miR398b negatively regulates cotton immune responses to Verticillium dahliae via multiple targets.

MicroRNAs (miRNAs) play essential roles in plant defense responses, although such roles have not been identified in cotton in response to the plant pathogenic fungus Verticillium dahliae. In this study, the functions of miR398b and its target genes in cotton-V. dahliae interaction were investigated. The transcript levels of miR398b were down-regulated by V. dahliae infection and miR398b overexpression in cotton made the plants more susceptible to V. dahliae. The results suggest that miR398b negatively regulates cotton resistance to V. dahliae. This may occur by miR398b repression of some CC-NBS-LRR genes via translational inhibition, interfering with defense responses and leading to cotton susceptibility to V. dahliae. Alternatively, miR398b may guide the cleavage of the mRNAs of GhCSD1, GhCSD2 and GhCCS, each of which functions in reactive oxygen species (ROS) regulation and homeostasis, thereby causing excessive ROS accumulation in miR398b-overexpressing plants in response to V. dahliae infection. This study suggests conserved and novel roles of miR398b in the cotton-V. dahliae interaction. These discoveries may be coupled with new strategies in cotton breeding programs to improve resistance to V. dahliae. [ABSTRACT FROM AUTHOR]