Disruption of OPR7 and OPR8 Reveals the Versatile Functions of Jasmonic Acid in Maize Development and Defense

Abstract

Here, multiple functions of jasmonic acid (JA) in maize (Zea mays) are revealed by comprehensive analyses of JA-deficient mutants of the two oxo-phytodienoate reductase genes, OPR7 and OPR8. Single mutants produce wild-type levels of JA in most tissues, but the double mutant opr7 opr8 has dramatically reduced JA in all organs tested. opr7 opr8 displayed strong developmental defects, including formation of a feminized tassel, initiation of female reproductive buds at each node, and extreme elongation of ear shanks; these defects were rescued by exogenous JA. These data provide evidence that JA is required for male sex determination and suppression of female reproductive organ biogenesis. Moreover, opr7 opr8 exhibited delayed leaf senescence accompanied by reduced ethylene and abscisic acid levels and lack of anthocyanin pigmentation of brace roots. Remarkably, opr7 opr8 is nonviable in nonsterile soil and under field conditions due to extreme susceptibility to a root-rotting oomycete (Pythium spp), demonstrating that these genes are necessary for maize survival in nature. Supporting the importance of JA in insect defense, opr7 opr8 is susceptible to beet armyworm. Overall, this study provides strong genetic evidence for the global roles of JA in maize development and immunity to pathogens and insects.

Ideal crop plant architecture is mediated by tassels replace upper ears1, a BTB/POZ ankyrin repeat gene directly targeted by TEOSINTE BRANCHED1

“…SLs, however, have been shown to function independently of tb1 (39), so its target gene tru1 may function independently as well. Jasmonic acid (JA) could be an additional hormone affected by TRU1 since knockouts of the JA biosynthetic genes OPR7/OPR8 in maize phenocopy tru1 ear shanks (40). It is possible that in domesticated maize, the ectopic expression of TRU1 in vascular leaf traces may move additional JA that minimizes internode elongation through the known effects of JA on suppression of mitosis (41).…”

Jasmonic acid regulates spikelet development in rice

“…In maize (Zea mays), Tasselseed1 (TS1) encodes a plastidtargeted lipoxygenase with predicted 13-lipoxygenase activity and participates in JA biosynthesis 46,47 . Two maize oxophytodienoate reductase genes, OPR7 and OPR8, were shown to participate in JA production 48 . Both ts1 and opr7 opr8 mutants convert staminate to pistillate in tassel inflorescence, indicating that JA is required for male sex determination and suppression of female reproductive organ biogenesis in maize [46][47][48] .…”

“…Two maize oxophytodienoate reductase genes, OPR7 and OPR8, were shown to participate in JA production 48 . Both ts1 and opr7 opr8 mutants convert staminate to pistillate in tassel inflorescence, indicating that JA is required for male sex determination and suppression of female reproductive organ biogenesis in maize [46][47][48] . Based on these results from other plant species and our own data, we propose that the conserved JA biosynthetic and signalling pathways play an important role in distinct aspects of reproductive development in various plant species, targeting different downstream genes.…”

Maize death acids, 9-lipoxygenase–derived cyclopente(a)nones, display activity as cytotoxic phytoalexins and transcriptional mediators

“…Diverse roles for JA and 12-OPDA as signals include developmental processes and inducible defenses against biotic threats (1-3, 7). Genetic evidence in maize (Zea mays) supports a role for JA biosynthesis in the survival of biotic stress, regulation of senescence, and cell death processes mediating male sex determination (8,9). As a precursor, 12-OPDA can trigger developmental processes and defense signaling different from JA-Ile (10)(11)(12).…”