MicroRNAs play essential roles during defense responses in plants, yet
their roles have not been widely functionally validated in cotton
response to Verticillium dahliae. Here, we employed transgenic
technology, virus induced gene silencing technology, as well as various
cytological and molecular tools to investigate the function of miR398b
and its target genes in cotton response to V. dahliae. 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 via two possibilities. One is that miR398b may repress
some CC-NBS-LRR genes during transcriptional or translational processes,
thereby interfering with defense responses of cotton to V. dahliae and
causing increased susceptibility of cotton to V. dahliae. Another
possibility is that miR398b may guide the cleavage of the mRNAs of
GhCSD1, GhCSD2 and GhCCS, which are important in the regulation of ROS
homeostasis, thereby leading to excessive ROS accumulation in
miR398b-overexpressing plants during V. dahliae infection. These studies
illuminate the conserved and novel roles of miR398b during the cotton-V.
dahliae interaction, which yields insights into new strategies to
improve resistance to V. dahliae in cotton breeding programs