SUMMARYIn nature, plants have to cope with a wide range of stress conditions that often occur simultaneously or in sequence. To investigate how plants cope with multi-stress conditions, we analyzed the dynamics of whole-transcriptome profiles of Arabidopsis thaliana exposed to six sequential double stresses inflicted by combinations of: (i) infection by the necrotrophic fungus Botrytis cinerea, (ii) herbivory by chewing larvae of Pieris rapae, and (iii) drought stress. Each of these stresses induced specific expression profiles over time, in which one-third of all differentially expressed genes was shared by at least two single stresses. Of these, 394 genes were differentially expressed during all three stress conditions, albeit often in opposite directions. When two stresses were applied in sequence, plants displayed transcriptome profiles that were very similar to the second stress, irrespective of the nature of the first stress. Nevertheless, significant first-stress signatures could be identified in the sequential stress profiles. Bioinformatic analysis of the dynamics of coexpressed gene clusters highlighted specific clusters and biological processes of which the timing of activation or repression was altered by a prior stress. The first-stress signatures in second stress transcriptional profiles were remarkably often related to responses to phytohormones, strengthening the notion that hormones are global modulators of interactions between different types of stress. Because prior stresses can affect the level of tolerance against a subsequent stress (e.g. prior herbivory strongly affected resistance to B. cinerea), the first-stress signatures can provide important leads for the identification of molecular players that are decisive in the interactions between stress response pathways.

Summary Plants are exposed to combinations of various biotic and abiotic stresses, but stress responses are usually investigated for single stresses only.Here, we investigated the genetic architecture underlying plant responses to 11 single stresses and several of their combinations by phenotyping 350 Arabidopsis thaliana accessions. A set of 214 000 single nucleotide polymorphisms (SNPs) was screened for marker‐trait associations in genome‐wide association (GWA) analyses using tailored multi‐trait mixed models.Stress responses that share phytohormonal signaling pathways also share genetic architecture underlying these responses. After removing the effects of general robustness, for the 30 most significant SNPs, average quantitative trait locus (QTL) effect sizes were larger for dual stresses than for single stresses.Plants appear to deploy broad‐spectrum defensive mechanisms influencing multiple traits in response to combined stresses. Association analyses identified QTLs with contrasting and with similar responses to biotic vs abiotic stresses, and below‐ground vs above‐ground stresses. Our approach allowed for an unprecedented comprehensive genetic analysis of how plants deal with a wide spectrum of stress conditions.

Background: Intracellular aggregation of polyglutamine (polyQ) proteins can be prevented by the chaperones DNAJB6 and DNAJB8. Results: DNAJB6 and DNAJB8 prevent the aggregation of pure polyQ peptides. Conclusion:The polyQ tract is sufficient for DNAJB6 and DNAJB8 to prevent aggregation. Significance: By interacting with polyQ fragments, DNAJB6 and DNAJB8 reduce polyQ protein aggregation and may be potential therapeutic targets in polyQ disorders.

Jasmonic acid (JA) regulates plant defenses against necrotrophic pathogens and insect herbivores. Salicylic acid (SA) and abscisic acid (ABA) can antagonize JA‐regulated defenses, thereby modulating pathogen or insect resistance. We performed a genome‐wide association (GWA) study on natural genetic variation in Arabidopsis thaliana for the effect of SA and ABA on the JA pathway. We treated 349 Arabidopsis accessions with methyl JA (MeJA), or a combination of MeJA and either SA or ABA, after which expression of the JA‐responsive marker gene PLANT DEFENSIN1.2 (PDF1.2) was quantified as a readout for GWA analysis. Both hormones antagonized MeJA‐induced PDF1.2 in the majority of the accessions but with a large variation in magnitude. GWA mapping of the SA‐ and ABA‐affected PDF1.2 expression data revealed loci associated with crosstalk. GLYI4 (encoding a glyoxalase) and ARR11 (encoding an Arabidopsis response regulator involved in cytokinin signalling) were confirmed by T‐DNA insertion mutant analysis to affect SA–JA crosstalk and resistance against the necrotroph Botrytis cinerea. In addition, At1g16310 (encoding a cation efflux family protein) was confirmed to affect ABA–JA crosstalk and susceptibility to Mamestra brassicae herbivory. Collectively, this GWA study identified novel players in JA hormone crosstalk with potential roles in the regulation of pathogen or insect resistance.

SummaryIn nature, plants are exposed to biotic and abiotic stresses that often occur simultaneously. Therefore, plant responses to combinations of stresses are most representative of how plants respond to stresses.We used RNAseq to assess temporal changes in the transcriptome of Arabidopsis thaliana to herbivory by Pieris rapae caterpillars, either alone or in combination with prior exposure to drought or infection with the necrotrophic fungus Botrytis cinerea.Pre-exposure to drought stress or Botrytis infection resulted in a significantly different timing of the caterpillar-induced transcriptional changes. Additionally, the combination of drought and P. rapae induced an extensive downregulation of A. thaliana genes involved in defence against pathogens. Despite a more substantial growth reduction observed for plants exposed to drought plus P. rapae feeding compared with P. rapae feeding alone, this did not affect weight increase of this specialist caterpillar.Plants respond to combined stresses with phenotypic and transcriptional changes that differ from the single stress situation. The effect of a previous exposure to drought or B. cinerea infection on transcriptional changes to caterpillars is largely overridden by the stress imposed by caterpillars, indicating that plants shift their response to the most recent stress applied.