Arabidopsis flower specific defense gene expression patterns affect resistance to pathogens

Abstract

We investigated whether the Arabidopsis flower evolved protective measures to increase reproductive success. Firstly, analyses of available transcriptome data show that the most highly expressed transcripts in the closed sepal (stage 12) are enriched in genes with roles in responses to chemical stimuli and cellular metabolic processes. At stage 15, there is enrichment in transcripts with a role in responses to biotic stimuli. Comparative analyses between the sepal and petal in the open flower mark an over-representation of transcripts with a role in responses to stress and catalytic activity. Secondly, the content of the biotic defense-associated phytohormone salicylic acid (SA) in sepals and petals is significantly higher than in leaves. To understand whether the high levels of stress responsive transcripts and the higher SA content affect defense, wild-type plants (Col-0) and transgenic plants defective in SA accumulation (nahG) were challenged with the biotrophic fungus Golovinomyces cichoracearum, the causal agent of powdery mildew, and the necrotrophic fungus Botrytis cinerea. NahG leaves were more sensitive than those of Col-0, suggesting that in leaves SA has a role in the defense against biotrophs. In contrast, sepals and petals of both genotypes were resistant to G. cichoracearum, indicating that in the flower, resistance to the biotrophic pathogen is not critically dependent on SA, but likely dependent on the up-regulation of stress-responsive genes. Since sepals and petals of both genotypes are equally susceptible to B. cinerea, we conclude that neither stress-response genes nor increased SA accumulation offers protection against the necrotrophic pathogen. These results are interpreted in the light of the distinctive role of the flower and we propose that in the early stages, the sepal may act as a chemical defense barrier of the developing reproductive structures against biotrophic pathogens.

RNA-Seq Links the Transcription Factors AINTEGUMENTA and AINTEGUMENTA-LIKE6 to Cell Wall Remodeling and Plant Defense Pathways

“…The increased expression of defense response genes in ant ail6 may be a consequence of sepals making up a larger part of ant ail6 flowers as compared with wild-type flowers. A recent analysis of publicly available transcriptomic data showed that defense genes are some of the most abundant transcripts in stage 12 to 15 sepals, suggesting that sepals play a key role in pathogen defense of the flower (Ederli et al, 2015). Thus, the increased defense gene expression in ant ail6 may partly or fully be an indirect effect resulting from changes in floral organ identity present in the double mutant.…”

Genomic evidence for population-specific responses to coevolving parasites in a New Zealand freshwater snail

“…Our inclusive analysis revealed 405 that the majority of transcripts that are significantly differentially expressed in infected snails are 406 downregulated relative to uninfected snails. This pattern could reflect several non-mutually 407 exclusive phenomena, ranging from tissue/organ destruction and/or overall poor condition of 408 infected snails (e.g., Barribeau et al 2014) to reallocation of resources to genes needed for 409 defence against and response to Microphallus infection (e.g., Ederli et al 2015) to suppression 410 and/or parasitic manipulation of P. antipodarum gene expression by Microphallus as a means of 411 evading host immune and defence systems (e.g., Levri & Lively 1996;Barribeau et al 2014;412 Soper et al 2014;de Bekker et al 2015). Regardless of the specific mechanism(s) involved, the 413 transcripts that are differentially expressed between infected and uninfected snails in the inclusive 414 analysis represent a set of genes that are most likely to be of general importance to the P. 415 antipodarum-Microphallus interaction.…”

Parasites, ploidy, and sex

“…This pattern is observed both overall (inclusive analysis) as well as within two of the three lakes (Alexandrina and Kaniere). Such patterns have been observed in other hostparasite interactions whereby exposure to and/or infection by parasites lead to systematic downregulation (e.g., de Bekker et al 2015;Ederli et al 2015). I also found that gene expression responses to M. livelyi infection tend to be population specific.…”

“…antipodarum are characterized by systematic downregulation of genes relative to uninfected P. antipodarum. This result could reflect several non-mutually exclusive scenarios such as the destruction of tissue (e.g., , reallocation of resources for defense purposes (e.g., Ederli et al 2015), and/or suppression or manipulation of host defenses by M. livelyi (e.g., de Bekker et al 2015). I also found that patterns of differential gene expression between infected and uninfected snails tend to be population specific, which provides the first genomic evidence consistent with ecological evidence for local adaptation and coevolution in this system.…”

“…Our inclusive analysis revealed that the majority of transcripts that are significantly differentially expressed in infected snails are downregulated relative to uninfected snails. This pattern could reflect several non-mutually exclusive phenomena, ranging from tissue/organ destruction and/or overall poor condition of infected snails (e.g., ) to reallocation of resources to genes needed for defence against and response to Microphallus infection (e.g., Ederli et al 2015) to suppression and/or parasitic manipulation of P. antipodarum gene expression by Microphallus as a means of evading host immune and defence systems (e.g., Levri & Lively 1996;Soper et al 2014;de Bekker et al 2015). It is also possible that some genes involved in resistance/susceptibility to infection were significantly differentially expressed between infected and uninfected snails prior to infection, potentially during exposure, such that the expression differences we characterize might affect whether a snail becomes infected vs. a consequence of infection per se (e.g., Keane et al 2006;Knight et al 2015).…”