A knock‐out mutation in allene oxide synthase results in male sterility and defective wound signal transduction in Arabidopsis due to a block in jasmonic acid biosynthesis

Abstract

SummaryRecent studies on jasmonic acid (JA) biosynthetic mutants have shown that jasmonates play essential roles in pollen maturation and dehiscence and wound-induced defence against biotic attacks. To better understand the biosynthetic mechanisms of this essential plant hormone, we isolated an Arabidopsis knock-out mutant defective in the JA biosynthetic gene CYP74A (allene oxide synthase, AOS) using reverse genetics screening methods. This enzyme catalyses dehydration of the hydroperoxide to an unstable allene oxide in the JA biosynthetic pathway. Endogenous JA levels, which increase 100-fold 1 h after wounding in wild-type plants, do not increase after wounding in the aos mutant. In addition, the mutant showed severe male sterility due to defects in anther and pollen development. The male-sterile phenotype was completely rescued by exogenous application of methyl jasomonate and by complementation with constitutive expression of the AOS gene. RT±PCR analysis showed that the induction of transcripts for vegetative storage protein and lipoxygenase genes, previously shown to be inducible by wound and jasmonate application in the wild-type, was absent in the aos mutant. In transgenic plants constitutively expressing AOS, wound-induced JA levels were 50±100% higher compared to wild-type plants. Taken together with JA de®ciency in the aos mutant, our results show that AOS is critical for the biosynthesis of all biologically active jasmonates. Our results also suggest that AOS expression is limiting JA levels in wounded plants, but that the AOS hydroperoxide substrate levels, controlled by upstream enzymes (lipoxygenase and phospholipase), determine JA levels in unwounded plants.

A bHLH-Type Transcription Factor, ABA-INDUCIBLE BHLH-TYPE TRANSCRIPTION FACTOR/JA-ASSOCIATED MYC2-LIKE1, Acts as a Repressor to Negatively Regulate Jasmonate Signaling inArabidopsis

“…Such phenotypes are similar to those reported for aos, opr3, defective in anther dehiscence1 (dad1), and coi1 mutants (Feys et al, 1994;Stintzi and Browse, 2000;Ishiguro et al, 2001;Park et al, 2002). The severity of male reproductive defects in Pro35:JAM1-SRDX lines correlated with transgene expression levels (see Supplemental Figures 5E and 5F online).…”

“…Mutants for ALLENE OXIDE SYNTHASE (AOS) or 12-OXOPHYTODIENOIC ACID REDUCTASE3 (OPR3)/ DELAYED DEHISCENCE1 have defects in endogenous JA production and reduced growth inhibition in response to wounding (Sanders et al, 2000;Stintzi and Browse, 2000;Park et al, 2002;Yan et al, 2007;Zhang and Turner, 2008). Wounding or JA application induces the expression of genes encoding JA biosynthetic enzymes and thus is expected to further increase JA production.…”

Jasmonic acid control of GLABRA3 links inducible defense and trichome patterning inArabidopsis

“…The following mutants and transgenic lines have been described previously: aos (Park et al, 2002); coi1-1 (Xie et al, 1998); egl3-7 (SALK_077439), gl1-20990 and gl3-sst (Esch et al, 2003); gl1-1 (Oppenheimer et al, 1991); gl1-2 (Esch et al, 1994); jar1-1 (Staswick et al, 2002); myb23-1 (Kirik et al, 2005); myc2-1 (Boter et al, 2004); sad2-2 (Verslues et al, 2006); GL1::GUS (Larkin et al, 1993); GL2::GUS (Szymanski et al, 1998); MYB23::GUS (Kirik et al, 2001); CPC::GFP ; VSP1::GUS (Ellis et al, 2001). aos and coi1-1 were backcrossed to wild type Col-0 because the original lines had gl1 markers and lacked trichomes.…”

“…To unequivocally address this issue, we used mutants completely lacking endogenous JA function. The aos mutant is deficient in JA biosynthesis owing to disruption of the ALLENE OXIDE SYNTHASE (AOS) gene, which encodes the key enzyme of JA biosynthesis (Park et al, 2002). Mechanical wounding of aos mutants did not increase trichome formation (Fig.…”

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

“…They also play pivotal roles in reproduction (Feys et al, 1994;McConn and Browse, 1996;Xie et al, 1998) and regulate many other plant developmental processes . Without JA, Arabidopsis thaliana plants, such as the JA biosynthetic mutants fad (McConn and Browse, 1996), opr3/dd1 (Sanders et al, 2000;Stintzi and Browse, 2000;Stintzi et al, 2001), and aos (Park et al, 2002), are unable to generate viable pollen and therefore fail to complete their life cycle. Without JA signaling or JA adenylation, Arabidopsis plants, including jar1 (Staswick et al, , 1998, coronatine insensitive1 (coi1) (Feys et al, 1994), and jin (Berger et al, 1996), are unresponsive to JA-inhibitory root growth, unable to accumulate JA-inducible genes, and susceptible to pest attack and pathogen infection.…”