Jasmonic Acid as a Mediator in Plant Response to Necrotrophic Fungi

Abstract

Jasmonic acid (JA) and its derivatives, all named jasmonates, are the simplest phytohormones which regulate multifarious plant physiological processes including development, growth and defense responses to various abiotic and biotic stress factors. Moreover, jasmonate plays an important mediator's role during plant interactions with necrotrophic oomycetes and fungi. Over the last 20 years of research on physiology and genetics of plant JA-dependent responses to pathogens and herbivorous insects, beginning from the discovery of the JA co-receptor CORONATINE INSENSITIVE1 (COI1), research has speeded up in gathering new knowledge on the complexity of plant innate immunity signaling. It has been observed that biosynthesis and accumulation of jasmonates are induced specifically in plants resistant to necrotrophic fungi (and also hemibiotrophs) such as mostly investigated model ones, i.e., Botrytis cinerea, Alternaria brassicicola or Sclerotinia sclerotiorum. However, it has to be emphasized that the activation of JA-dependent responses takes place also during susceptible interactions of plants with necrotrophic fungi. Nevertheless, many steps of JA function and signaling in plant resistance and susceptibility to necrotrophs still remain obscure. The purpose of this review is to highlight and summarize the main findings on selected steps of JA biosynthesis, perception and regulation in the context of plant defense responses to necrotrophic fungal pathogens.

Keywords: COI1; circadian clock; defense responses; jasmonates; necrotrophic fungi; resistance; signaling.

Figure 2

Infection of a plant within foliar tissues with a necrotrophic fungus triggers JA biosynthesis and JA perception via COI1 receptor complex regulated with JAZs and subsequent JA-dependent signal transduction through transcription factors such as WRKY75 and/or MYC2 and downstream expression of defense-related genes such as PDF1.2, VSP2 and LOX2. JA-responsive gene ORA59 was detected exclusively as being activated downstream WRKY75 [12,112,120]. Detailed description in the text.

Figure 1

Biosynthesis pathway of jasmonates in Arabidopsis active during necrotrophic interactions [1,2,3,9,30,32,33,34,35]. Detailed description in the text. Abbreviations: ACX, acyl-CoA oxidase; AOC, allene oxide cyclase; AOS, allene oxide synthase; 12,13-EOT, 12,13(S)-epoxy-9(Z),11,15(Z)-octadecatrienoic acid; (+)-7-iso-JA, (+)-7-iso-jasmonic acid; (+)-7-iso-JA-Ile, (+)-7-iso-jasmonoyl-L-isoleucine; JMT, JA carboxyl methyl transferase; JAR1, Jasmonate-Resistant synthase; JA-Me, methyl ester of JA; JA-Phe, jasmonoyl-phenylalanine; 13-HPOT, (13S)-hydroperoxy-octadecatrienoic acid; KAT, l-3-ketoacyl-CoA thiolase; 13-LOX, 13-lipoxygenase; OPC-8, 3-oxo-2-(2′-[Z]-pentenyl)cyclopentane-1-octanoic acid; cis-(+)-12-OPDA, cis-(+)-12-oxo-phytodienoic acid; OPR3, 12-oxo-phytodienoic acid reductase; PLA1, phospholipase A1.