Bacterial and plant natriuretic peptides improve plant defence responses against pathogens

Abstract

Plant natriuretic peptides (PNPs) have been implicated in the regulation of ions and water homeostasis, and their participation in the plant immune response has also been proposed. Xanthomonas citri ssp. citri contains a gene encoding a PNP-like protein (XacPNP) which has no homologues in other bacteria. XacPNP mimics its Arabidopsis thaliana homologue AtPNP-A by modifying host responses to create favourable conditions for pathogen survival. However, the ability of XacPNP to induce plant defence responses has not been investigated. In order to study further the role of XacPNP in vivo, A. thaliana lines over-expressing XacPNP, lines over-expressing AtPNP-A and AtPNP-A-deficient plants were generated. Plants over-expressing XacPNP or AtPNP-A showed larger stomatal aperture and were more resistant to saline or oxidative stress than were PNP-deficient lines. In order to study further the role of PNP in biotic stress responses, A. thaliana leaves were infiltrated with pure recombinant XacPNP, and showed enhanced expression of genes related to the defence response and a higher resistance to pathogen infections. Moreover, AtPNP-A expression increased in A. thaliana on Pseudomonas syringae pv. tomato (Pst) infection. This evidence led us to analyse the responses of the transgenic plants to pathogens. Plants over-expressing XacPNP or AtPNP-A were more resistant to Pst infection than control plants, whereas PNP-deficient plants were more susceptible and showed a stronger hypersensitive response when challenged with non-host bacteria. Therefore, XacPNP, acquired by horizontal gene transfer, is able to mimic PNP functions, even with an increase in plant defence responses.

PLANT NATRIURETIC PEPTIDE A antagonizes salicylic acid-primed cell death

“…Recently, the response of plants overexpressing Arabidopsis PNP-A to a bacterial pathogen was examined: the results show that PNP-A potentiates the expression of defense-related genes, including PR1 , conferring increased resistance to Pseudomonas syringae pv. tomato ( Pst ) DC3000 infection 20 . This is, however, inconsistent with our finding that PNP-A negatively regulates the expression of PR genes along with other SA-responsive genes in lsd1 .…”

“…All the Arabidopsis genotypes used in this study are Columbia (Col-0) ecotype. Arabidopsis mutant seeds of lsd1-2 (SALK_042687) 27 , pnp-A (SALK_000951) 15,20 , npr1 (SALK_204100), pnpar-1 (GABIseq_255A11.1), pnpar-2 (SALKseq_6749.3), and pnp-r1 (GABI-KAT_180G04) 15 were obtained from the Nottingham Arabidopsis Stock Centre (NASC). We generated and genotyped double mutants by crossing homozygous single mutant plants and using appropriate primers (Supplementary Table 2).…”

“…Like ANPs, upon secretion to the apoplast, PNPs undergo formation of inter-disulfide bonds and proteolytic processing 15,17 . Although PNPs have been shown to affect a broad spectrum of physiological responses in plants, including stomata opening 14,18–20 , regulation of photosynthetic efficiency and photorespiration 19,21 , cellular water and ion (Ca 2+ , H + , K + and Na + ) homeostasis 13,15,22 , increase in protoplast volume 14,15 , modulation of their own expression 23,24 and resistance against biotic and abiotic stresses 20 , their mode of action is largely unclear and their cognate receptor proteins are unknown.…”

Transcriptomic analysis of Arabidopsis thaliana plants treated with the Ky-9 and Ky-72 histone deacetylase inhibitors

“…18 A recent study concluded that AtPNP-A knockout mutants and plants overexpressing AtPNP-A are hypersensitive and tolerant to high-salinity stress conditions, respectively. 19 The upregulated expression of PNP-A due to Ky-9 or Ky-72 treatments may initiate downstream cascades to enable plants to overcome the effects of high-salinity stress.…”

Virulence contribution and recognition of homologs of the Verticillium dahliae effector Ave1

“…Also Verticillium dahliae effector Ave1 has homologs in other plant pathogens, including the fungi Fusarium oxysporum, Colletotrichum higginsianum, Cercospora beticola and the bacterium Xanthomonas axonopodis . In these organisms, the Ave1 homologs act as virulence factor as well (Ficarra et al 2017;, with the exception of C. higginsianum (Chapter 3, this thesis). In addition, multiple Ave1 homologs were identified in the fungi Venturia inaequalis and V. pirina that are pathogens of apple and pear, respectively (Chapter 5, this thesis) Deng et al 2017).…”