Allene Oxide Synthase Pathway in Cereal Roots: Detection of Novel Oxylipin Graminoxins

Abstract

Young roots of wheat, barley, and sorghum, as well as methyl jasmonate pretreated rice seedlings, undergo an unprecedented allene oxide synthase pathway targeted to previously unknown oxylipins 1–3. These Favorskii‐type products, (4Z)‐2‐pentyl‐4‐tridecene‐1,13‐dioic acid (1), (2′Z)‐2‐(2′‐octenyl)‐decane‐1,10‐dioic acid (2), and (2′Z,5′Z)‐2‐(2′,5′‐octadienyl)‐decane‐1,10‐dioic acid (3), have a carboxy function at the side chain, as revealed by their MS and NMR spectral data. Compounds 1–3 were the major oxylipins detected, along with the related α‐ketols. Products 1–3 were biosynthesized from (9Z,11E,13S)‐13‐hydroperoxy‐9,11‐octadecadienoic acid, (9S,10E,12Z)‐9‐hydroperoxy‐10,12‐octadecadienoic acid (9‐HPOD), and (9S,10E,12Z,15Z)‐9‐hydroperoxy‐10,12,15‐octadecatrienoic acid, respectively, via the corresponding allene oxides and cyclopropanones. The data indicate that conversion of the allene oxide into the cyclopropanone is controlled by soluble cyclase. The short‐lived cyclopropanones are hydrolyzed to products 1–3. The collective name “graminoxins” has been ascribed to oxylipins 1–3.

Jasmonates: News on Occurrence, Biosynthesis, Metabolism and Action of an Ancient Group of Signaling Compounds

“…In contrast, low levels of JA occurring in precious ( pre ) rice mutant due to a mutated OsAOS1, attribute to a long leaf phenotype [ 69 ] suggesting that JA is a negative regulator in vegetative development [ 69 ]. A new group of oxylipins which are generated via the AOS pathway, has been identified in cereals [ 70 ]. These so-called graminoxines are formed from compounds such as (9 Z ,11 E ,13 S )-13-hydroperoxy-9,11-octadecadienoic acid via hydrolysis of a short lived AOS-generated cyclopentanone to (4 Z )-2-pentyl-4-tridecene-1, 13-dienoic acid (graminoxin A1), which has a carboxy function at the side chain.…”

Jasmonates: what ALLENE OXIDE SYNTHASE does for plants

“…Due to their relatively large masses, AOS-derived oxylipins can display great structural diversity; new examples of these compounds are frequently discovered. For example, Grechkin et al (2018) discovered that young roots of wheat and rice produce a remarkable group of AOS-derived branched-chain oxylipins that they term ‘graminoxins’. Together with an earlier report of cyclic, pathogen-induced AOS products known as ‘death acids’ in maize (Christensen et al , 2015), these studies reveal the enormous potential to discover novel oxylipins.…”

Cloning of wheat keto-acyl thiolase 2B reveals a role of jasmonic acid in grain weight determination

“…After centrifugation at 3000 × g for 20 min, the supernatant was assayed by an ELISA kit (Zhen Ke Biological Technology Co., Ltd., Shanghai, China). Oxidized lipid analysis was performed according to previous literature 52 . In brief, 2 gm of the fully expanded leaf was collected in the field and ground into fine powder in liquid nitrogen in a high-though put homogenizer.…”

“…The sample was dried and analyzed by GC/MS. Oxidized lipid characterization was performed based on the mass spectrum, according to a literature 52 .…”