A role for jasmonate in pathogen defense of Arabidopsis

Abstract

To investigate the role of jasmonate in the defense of plants against fungal pathogens, we have studied a mutant of Arabidopsis, fad3-2 fad7-2 fad8, that cannot accumulate jasmonate. Mutant plants were extremely susceptible to root rot caused by the fungal root pathogen Pythium mastophorum (Drechs.), even though neighboring wild-type plants were largely unaffected by this fungus. Application of exogenous methyl jasmonate substantially protected mutant plants, reducing the incidence of disease to a level close to that of wild-type controls. A similar treatment with methyl jasmonate did not protect the jasmonate-insensitive mutant coi1 from infection, showing that protective action of applied jasmonate against P. mastophorum was mediated by the induction of plant defense mechanisms rather than by a direct antifungal action. Transcripts of three jasmonate-responsive defense genes are induced by Pythium challenge in the wildtype but not in the jasmonate-deficient mutant. Pythium species are ubiquitous in soil and root habitats world-wide, but most (including P. mastophorum) are considered to be minor pathogens. Our results indicate that jasmonate is essential for plant defense against Pythium and, because of the high exposure of plant roots to Pythium inoculum in soil, may well be fundamental to survival of plants in nature. Our results further indicate that the fad3-2 fad7-2 fad8 mutant is an appropriate genetic model for studying the role of this important signaling molecule in pathogen defense.

Fusarium oxysporum hijacks COI1‐mediated jasmonate signaling to promote disease development in Arabidopsis

“…However, coi1 also displays enhanced susceptibility to the soil-borne oomycete pathogens Pythium irregulare (Adie et al, 2007) and Pythium mastophorum (Vijayan et al, 1998), as well as the vascular wilt-inciting fungal pathogen Verticillium longispo- rum (Johansson et al, 2006), suggesting that the effect of the coi1 mutation in restricting disease symptom development is more specific to F. oxysporum. Interestingly, coi1 also exhibited reduced susceptibility to the soil-borne bacterial wilt pathogen Ralstonia solanacearum (Hernandez-Blanco et al, 2007), and to root-knot nematodes (Meloidogyne spp.)…”

Salicylic acid-independent plant defence pathways

“…Depending on the type of invader encountered, the plant appears to be capable of switching on the appropriate pathway or combination of pathways. The plant signalling molecules salicylic acid, jasmonic acid and ethylene play an important role in this signalling network: blocking the response to either of these signals can render plants more susceptible to pathogens and even insects 6, [49][50][51][52] . Resistance conferred by the salicylic acid-dependent pathway might be directed more against certain types of pathogens, whereas resistance conferred by salicylic acid-independent pathways might operate more effectively against other types of pathogens.…”

COS1: An Arabidopsis coronatine insensitive1 Suppressor Essential for Regulation of Jasmonate-Mediated Plant Defense and Senescence

“…The coi1 mutations previously were found to cause loss of resistance against insects and pathogens in Arabidopsis (McConn et al, 1997;Vijayan et al, 1998;Stintzi et al, 2001). To investigate whether the cos1 mutation restores the defense responses in coi1-2, we inoculated the fungus pathogen (Botrytis cinerea) onto the wild type, coi1-2, and cos1 coi1-2 (Figure 3).…”

“…The recessive coi1 mutants fail to respond to JA and coronatine, a phytotoxin structurally similar to jasmonic acid (Feys et al, 1994), displaying defects in JA-regulated gene expression, exhibiting male sterility, and showing susceptibility to insect attack and pathogen infection (Feys et al, 1994;McConn et al, 1997;Vijayan et al, 1998;Reymond et al, 2000;Stintzi et al, 2001;Feng et al, 2003). The COI1 gene encodes a 592-amino acid protein containing an F-box motif and 16 leucine-rich repeat sequences (Xie et al, 1998), which interact with Arabidopsis CULLIN1, RBX1, and Skp1-like proteins ASK1 or ASK2 to assemble SCF COI1 complexes in planta (Xu et al, 2002).…”