Through parental or transgenerational effects, biotic and abiotic cues can have heritable effects on phenotypes in subsequent generations. It is often speculated that such inherited environmental effects might prime offspring for enhanced stress or defense responses when exposed to similar environmental stresses as their parents. However, it is not clear how common such effects are and the underlying mechanisms remain poorly understood. Here we tested the effects of parental jasmonic acid (JA) treatment, which is involved in herbivory-induced defense signaling, on offspring gene expression and leaf chemistry in apomictic common dandelion plants (Taraxacum officinale). Due to apomictic reproduction from a single founder individual, the effects of genetic variation between experimental plants are negligible in this multi-generational experiment. We exposed two subsequent generations to either jasmonic acid or control treatment, and performed RNA-seq gene expression profiling and LC-MS metabolomics profiling in third-generation plants both after jasmonic acid and control treatments. Using a de novo assembled transcriptome based on Illumina RNA-Seq, we identified 551 contigs that are differentially expressed after direct JA treatment. Expression of an additional 307 contigs showed a significant effect of parental JA treatment or of the parental x offspring JA treatment interaction. Gene ontology enrichment analysis validated the induction of JA-associated herbivory stress responses, but no such functional signal could be detected in the genes that showed a transgenerational JA effect. LC-MS metabolomics profiling, and also targeted analysis of leaf total phenolics which have known anti-herbivore and anti-microbial function, showed clear effects of direct JA treatment and weaker, but still detectable, effects of parental JA treatment.
These results indicate inherited gene expression effects of parental and/or grandparental JA treatment, associated with effects on leaf chemistry including leaf secondary defense compounds. The observations are consistent with transgenerational priming of defense responses. The inherited effects could be mediated by epigenetic mechanisms, but this remains to be demonstrated. Given the observed nontrivial effects of parental environment on gene expression profiles, we stress the importance of controlling for parental environmental conditions in transcriptomic studies.
|Date made available||30 Mar 2016|