Light induces jasmonate‐isoleucine conjugation via OsJAR1‐dependent and ‐independent pathways in rice

Abstract

The bioactive form of jasmonate is the conjugate of the amino acid isoleucine (Ile) with jasmonic acid (JA), which is biosynthesized in a reaction catalysed by the GH3 enzyme JASMONATE RESISTANT 1 (JAR1). We examined the biochemical properties of OsJAR1 and its involvement in photomorphogenesis of rice (Oryza sativa). OsJAR1 has a similar substrate specificities as its orthologue in Arabidopsis. However, osjar1 loss-of-function mutants did not show as severe coleoptile phenotypes as the JA-deficient mutants coleoptile photomorphogenesis 2 (cpm2) and hebiba, which develop long coleoptiles in all light qualities we examined. Analysis of hormonal contents in the young seedling stage revealed that osjar1 mutants are still able to synthesize JA-Ile conjugate in response to blue light, suggesting that a redundantly active enzyme can conjugate JA and Ile in rice seedlings. A good candidate for this enzyme is OsJAR2, which was found to be able to catalyse the conjugation of JA with Ile as well as with some additional amino acids. In contrast, if plants in the vegetative stage were mechanically wounded, the content of JA-Ile was severely reduced in osjar1, demonstrating that OsJAR1 is the most important JA-Ile conjugating enzyme in the wounding response during the vegetative stage.

Changes in the chlorophyll content of grape leaves could provide a physiological index for responses and adaptation to UV‐C radiation

“…Total RNA was isolated (Ismail et al 2012, Duan et al 2015 using the SpectrumÔ Plant Total RNA Kit, treated with a DNA-free DNase and transcribed into cDNA using the M-MuLV cDNA Synthesis Kit. Quantitative real-time PCR was performed as previously described (Svyatyna et al 2014). To compare the mRNA expression levels between different samples, the C t values from each sample were normalized to the value for the EF-1α internal standard.…”

Induced Jasmonate Signaling Leads to Contrasting Effects on Root Damage and Herbivore Performance

“…Rice is a suitable model for this purpose, because several genes involved in jasmonate biosynthesis have been identified (Zhou et al, 2009;Qi et al, 2011a;Riemann et al, 2013;Svyatyna et al, 2014), and jasmonate-deficient genotypes are available (Riemann et al, 2003;Zhou et al, 2009). Furthermore, rice plants are frequently attacked by root herbivores in the field, including the major pest rice water weevil whose larvae feed on rice roots under flooded conditions and obtain their oxygen directly through the root aerenchyma (Saito et al, 2005), as well as other generalist herbivores, such as the cucumber beetle (Diabrotica balteata), which is not a major pest of rice but has been reported to feed on rice occasionally.…”

Jasmonic acid‐isoleucine formation in grapevine (Vitis vinifera L.) by two enzymes with distinct transcription profiles

“…Nevertheless, VvGH3‐7‐catalysed conjugation of JA to Ile, Leu, Met, Val Ser, Thr, Cys and His could be demonstrated by either TLC and/or LC‐MS (Figures 1B, C, 2B), whereas SA, IAA, OPDA and dnOPDA were not accepted as acyl substrates (data not shown). The substrate specificity of VvGH3‐7 therefore resembled that of VvGH3‐9 and the rice protein OsJAR2, which clusters into the monocot subgroup II (Wakuta et al ; Svyatyna et al ).…”

“…VvGH3‐9 is the orthologue of Arabidopsis GH3‐11 (JAR1) and clusters into dicot subgroup I of Group I proteins (Wakuta et al ). All characterized members of this subgroup, as well as the closely related monocot subgroup I, have been described as JA‐conjugating enzymes that catalyze the formation of a range of JA‐amino acid conjugates, including JA‐Ile (Staswick and Tiryaki ; Suza et al ; Wakuta et al ; Svyatyna et al ). Purified, recombinant VvGH3‐9 protein (Figure A) was found to conjugate a total of 12 amino acids to JA.…”

“…Two JA‐conjugating GH3 enzymes from tobacco ( Nicotiana tabacum L.), NaJAR4 and NaJAR6, have been implicated in the response to wounding and herbivore attack (Kang et al ; Wang et al ). Rice (Oryza sativa L.) also contains two functional Group I GH3 proteins and both of them were shown to be involved in the wound response in seedlings (Wakuta et al ; Svyatyna et al ). In addition, OsJAR1 mRNA levels were increased by pathogen infection (Wakuta et al ) and recent studies using the corresponding mutant have established OsJAR1 as the main JA‐conjugating enzyme involved in the wound response in adult rice plants (Fukumoto et al ; Shimizu et al ; Svyatyna et al ).…”