DELLAs Control Plant Immune Responses by Modulating the Balance of Jasmonic Acid and Salicylic Acid Signaling

In Arabidopsis, the flagellin-derived peptide flg22 elevates antibacterial resistance [1Zipfel C. Robatzek S. Navarro L. Oakeley E.J. Jones J.D. Felix G. Boller T. Bacterial disease resistance in Arabidopsis through flagellin perception.Nature. 2004; 428: 764-767Crossref PubMed Scopus (1124) Google Scholar] and inhibits growth [2Gomez-Gomez L. Felix G. Boller T. A single locus determines sensitivity to bacterial flagellin in Arabidopsis thaliana.Plant J. 1999; 18: 277-284Crossref PubMed Scopus (481) Google Scholar] upon perception via the leucine-rich repeat receptor-like kinase Flagellin-Sensitive 2 (FLS2) [3Gomez-Gomez L. Boller T. FLS2: An LRR receptor-like kinase involved in the perception of the bacterial elicitor flagellin in Arabidopsis.Mol. Cell. 2000; 5: 1003-1011Abstract Full Text Full Text PDF PubMed Google Scholar]. DELLA proteins are plant growth repressors whose degradation is promoted by the phytohormone gibberellin [4Sun T.P. Gubler F. Molecular mechanism of gibberellin signaling in plants.Annu. Rev. Plant Biol. 2004; 55: 197-223Crossref PubMed Scopus (513) Google Scholar]. Here, we show that DELLA stabilization contributes to flg22-induced growth inhibition. In addition, we show that DELLAs promote susceptibility to virulent biotrophs and resistance to necrotrophs, partly by altering the relative strength of salicylic acid and jasmonic acid (JA) signaling. A quadruple-DELLA mutant (which lacks four out of the five Arabidopsis DELLA proteins [5Cheng H. Qin L. Lee S. Fu X. Richards D.E. Cao D. Luo D. Harberd N.P. Peng J. Gibberellin regulates Arabidopsis floral development via suppression of DELLA protein function.Development. 2004; 131: 1055-1064Crossref PubMed Scopus (381) Google Scholar]) was partially insensitive to gene induction by Methyl-Jasmonate (MeJA), whereas the constitutively active dominant DELLA mutant gai [6Peng J. Carol P. Richards D.E. King K.E. Cowling R.J. Murphy G.P. Harberd N.P. The Arabidopsis GAI gene defines a signaling pathway that negatively regulates gibberellin responses.Genes Dev. 1997; 11: 3194-3205Crossref PubMed Scopus (810) Google Scholar] was sensitized for JA-responsive gene induction, implicating DELLAs in JA-signaling and/or perception. Accordingly, the elevated resistance of gai to the necrotrophic fungus Alternaria brassicicola and susceptibility to the hemibiotroph Pseudomonas syringae pv. tomato strain DC3000 (Pto DC3000) was attenuated in the JA-insensitive coi1-16 mutant [7Ellis C. Turner J.G. A conditionally fertile coi1 allele indicates cross-talk between plant hormone signalling pathways in Arabidopsis thaliana seeds and young seedlings.Planta. 2002; 215: 549-556Crossref PubMed Scopus (146) Google Scholar]. These findings suggest an explanation for why the necrotrophic fungus Gibberella fujikuroi, causal agent of the foolish-seedling disease of rice, makes gibberellin.