Transcriptional profiling of methyl jasmonate-induced defense responses in bilberry (Vaccinium myrtillus L.)

Authors: FONSECA BENEVENUTO, RAFAEL - Western Norway University Of Applied Sciences; SELDAL, TARALD - Western Norway University Of Applied Sciences; HEGLAND, STEIN - Western Norway University Of Applied Sciences; RODRIGUEZ-SAONA, CESAR - Rutgers University; KAWASH, JOSEPH - Orise Fellow; Polashock, James

Submitted to: BMC Plant Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/14/2019
Publication Date: 2/12/2019
Citation: Fonseca Benevenuto, R., Seldal, T., Hegland, S.J., Rodriguez-Saona, C., Kawash, J., Polashock, J.J. 2019. Transcriptional profiling of methyl jasmonate-induced defense responses in bilberry (Vaccinium myrtillus L.). Biomed Central (BMC) Plant Biology. 19:70. https://doi.org/10.1186/s12870-019-1650-0.
DOI: https://doi.org/10.1186/s12870-019-1650-0

Interpretive Summary: European bilberry is related to the blueberries that are cultivated in North America. It is an important understory shrub and the fruit are know for their bioactive compounds, including those that deter insects that eat the leaves. We studied how the plant uses hormones to regulate plants genes in response to insect chewing and stimulate defense against further insect damage. Specifically, we studied the genes that are 'turned on' or 'turned off' when attacked by insects. We found that genes involved in the biosynthesis of plant cell wall strengthening and compounds that deter insects were turned on while those associated with normal growth and reproduction were turned off. This suggests that turning on defenses is energetically costly, and to compensate, the plant reduces the amount of resources allocated for growth and reproduction. This information is useful to scientists studying similar interactions in plants. A better understanding of how plants respond to environmental stresses, including insect attack, can be used to breed or engineer plants that continue to grow and produce fruit under stressful conditions.

Technical Abstract: Bilberry (Vaccinium myrtillus L.) is one of the most abundant wild berries in the Northern European ecosystems. This species plays an important ecological role as a food source for many vertebrate and invertebrate herbivores. It is also well-recognized for its bioactive compounds, particularly substances involved in natural defenses against herbivory. These defenses are known to be initiated by leaf damage (e.g. chewing by insects) and mediated by activation of the jasmonic acid (JA) signaling pathway. This pathway can be activated by exogenous application of methyl jasmonate (MeJA), the volatile derivative of JA, which is often used to stimulate plant defense responses in studies of plant-herbivore interactions at ecological, biochemical, and molecular organismal levels. As a proxy for herbivore damage, wild V. myrtillus plants were treated in the field with MeJA and changes in gene expression were compared to untreated plants. The de novo transcriptome assembly consisted of 231,887 unigenes. Nearly 71% of the unigenes were annotated in at least one of the databases interrogated. Differentially expressed genes (DEGs), between MeJA-treated and untreated control bilberry plants were identified using DESeq. A total of 3,590 DEGs were identified between the treated and control plants, with 2,013 DEGs upregulated and 1,577 downregulated. The majority of the DEGs identified were associated with primary and secondary metabolism pathways in plants. DEGs associated with growth (e.g. those encoding photosynthesis-related components) and reproduction (e.g. flowering control genes) were frequently down-regulated while those associated with defense (e.g. encoding enzymes involved in biosynthesis of flavonoids, lignin compounds, and deterrent/repellent VOCs) were up-regulated in the MeJA treated plants. Ecological studies are often limited by controlled conditions to reduce the impact of environmental effects. The results from this study support the hypothesis that bilberry plants, growing in natural conditions, shift resources from growth and reproduction to defenses under a MeJA-induced state indicative of insect attack. This study highlights the occurrence of this trade-off at the transcriptional level in a realistic field scenario and supports published field observations wherein plant growth is retarded and defenses are upregulated.