Sexual dimorphism, including differences in morphology, behavior and physiology
between males and females, is widespread in animals and plants and is shaped by
gene expression differences between the sexes. Such expression differences may also
underlie sex-specific responses of hosts to pathogen infections, most notably when
pathogens induce partial sex reversal in infected hosts. The genetic changes
associated with sexual dimorphism, on the one hand, and sex-specific responses to
pathogen infections, on the other hand, remain poorly understood. The dioecious
White Campion (Silene latifolia) displays strong sexual dimorphism in floral traits and
infection with the smut fungus Microbotryum violaceum induces a partial sex reversal in
females, rendering them more male-like. We find strong sex-specific responses to
pathogen infection in S. latifolia. This allows for the first time to link pathogen-mediated
changes in sex-biased gene expression to altered sexual dimorphism in the host. In
females, expression changes following infection led to transcriptome defeminization
and masculinization, whereas in males, infection caused widespread down-regulation
of contigs with male-biased expression in healthy plants, leading to opposite changes
of expression patterns, and thus to feminization and demasculinization of the
transcriptome in response to smut infection. These transcriptional changes included
activation of sex-specific genes in the opposite sex and were associated with a partial
sex reversal in females and reduced sexual dimorphism between infected male and
female hosts. Our results reveal strong sex-specific responses to pathogen infection in
a dioecious plant and provide a link between changes in sex-biased gene expression
and sexual dimorphism. Less...