Search

GO analysis of genes specifically upregulated by combined stress. GO terms significantly enriched with each combined stress are shown separately. Length of the bars shows the percentage of regulated genes in the respective GO categories. (PDF 951Â kb)

GO analysis of genes specifically downregulated by combined stress. GO analysis of genes specifically downregulated by combined stress. GO terms significantly enriched with each combined stress are shown separately. Length of the bars shows the percentage of regulated genes in the respective GO categories. (PDF 918Â kb)

Expression of the top-50 upregulated genes in response to P. brassicae feeding and combined stresses. The highest significantly upregulated genes (log2 > 0.585, P

Quantification of defense signals and glucosinolates. (A) Experimental design. (B) Quantification of jasmonic acid (JA), salicylic acid (SA) and total glucosinolates (GS) in single and combined stress in whole 5-week-old B. nigra leaves. Plants were pretreated for 3 days with P. brassicae egg extract (EE) or Xanthomonas campestris pv. raphani (Xcr) and further challenged with P. brassicae (P) larvae for 24 h. Controls (CTL) consisted of untreated plants or plants exposed to a single treatment. Values (± SE) are the mean of three independent experiments. Letters indicate significant difference between treatments (two-way ANOVA followed by Tukey’s honest significant difference test, P

Expression of glucosinolate biosynthesis genes in response to P. brassicae feeding and combined stresses. Values were extracted from microarray data. P. brassicae larvae (orange bars), egg extract/P. brassicae larvae (yellow bars), Xanthomonas campestris pv. raphani/P. brassicae (green bars), Brevicoryne brassicae/P. brassicae (blue bars). Significant differences between single and combined stress are indicated (Student’s t-test, ***P

Background In nature, plants are frequently exposed to simultaneous biotic stresses that activate distinct and often antagonistic defense signaling pathways. How plants integrate this information and whether they prioritize one stress over the other is not well understood. Results We investigated the transcriptome signature of the wild annual crucifer, Brassica nigra, in response to eggs and caterpillars of Pieris brassicae butterflies, Brevicoryne brassicae aphids and the bacterial phytopathogen Xanthomonas campestris pv. raphani (Xcr). Pretreatment with egg extract, aphids, or Xcr had a weak impact on the subsequent transcriptome profile of plants challenged with caterpillars, suggesting that the second stress dominates the transcriptional response. Nevertheless, P. brassicae larval performance was strongly affected by egg extract or Xcr pretreatment and depended on the site where the initial stress was applied. Although egg extract and Xcr pretreatments inhibited insect-induced defense gene expression, suggesting salicylic acid (SA)/jasmonic acid (JA) pathway cross talk, this was not strictly correlated with larval performance. Conclusion These results emphasize the need to better integrate plant responses at different levels of biological organization and to consider localized effects in order to predict the consequence of multiple stresses on plant resistance. Electronic supplementary material The online version of this article (doi:10.1186/s12870-017-1074-7) contains supplementary material, which is available to authorized users.

Glucosinolate content in B. nigra leaves. (PDF 37Â kb)

Expression of the top-50 downregulated genes in response to P. brassicae feeding and combined stresses. The highest significantly downregulated genes (log2

List of primers used for QPCR. (PDF 51Â kb)

Feeding behavior of P. brassicae larvae in response to combined stresses. Neonate larvae were allowed to feed freely for 2 days (P. brassicae) on 5-week-old B. nigra plants pretreated for 3 days with egg extract (A) or Xanthomonas campestris pv. raphani (B). Representative images from three biological replicates are shown. Scale bar = 1 cm. (PDF 9284 kb)

GO analysis of P. brassicae-regulated genes. (PDF 49Â kb)