Crosstalk and differential response to abiotic and biotic stressors reflected at the transcriptional level of effector genes from secondary metabolism

Plant secondary metabolism significantly contributes to defensive measures against adverse abiotic and biotic cues. To investigate stress-induced, transcriptional alterations of underlying effector gene families, which encode enzymes acting consecutively in secondary metabolism and defense reactions, a DNA array (MetArray) harboring gene-specific probes was established. It comprised complete sets of genes encoding 109 secondary product glycosyltransferases and 63 glutathione-utilizing enzymes along with 62 cytochrome P450 monooxygenases and 26 ABC transporters. Their transcriptome was monitored in different organs of unstressed plants and in shoots in response to herbicides, UV-B radiation, endogenous stress hormones, and pathogen infection. A principal component analysis based on the transcription of these effector gene families defined distinct responses and crosstalk. Methyl jasmonate and ethylene treatments were separated from a group combining reactions towards two sulfonylurea herbicides, salicylate and an avirulent strain of Pseudomonas syringae pv. tomato. The responses to the herbicide bromoxynil and UV-B radiation were distinct from both groups. In addition, these analyses pinpointed individual effector genes indicating their role in these stress responses. A small group of genes was diagnostic in differentiating the response to two herbicide classes used. Interestingly, a subset of genes induced by P. syringae was not responsive to the applied stress hormones. Small groups of comprehensively induced effector genes indicate common defense strategies. Furthermore, homologous members within branches of these effector gene families displayed differential expression patterns either in both organs or during stress responses arguing for their non-redundant functions.