Methyl zealactonoate, a novel germination stimulant for root parasitic weeds produced by maize

Abstract

One of the germination stimulants for root parasitic weeds produced by maize (Zea mays) was isolated and named methyl zealactonoate (1). Its structure was determined to be methyl (2E,3E)-4-((RS)-3,3-dimethyl-2-(3-methylbut-2-en-2-yl)-5-oxotetrahydrofuran-2-yl)-2-((((R)-4-methyl-5-oxo-2,5-dihydrofran-2-yl)oxy)methylene)but-3-enoate using by 1D and 2D NMR spectroscopy and ESI and EI-MS spectrometry. Feeding experiments with 13 C-carlactone (CL), a biosynthetic intermediate for strigolactones, confirmed that 1 is produced from CL in maize. Methyl zealactonoate strongly elicits Striga hermonthica and Phelipanche ramosa seed germination, while Orobanche minor seeds are 100-fold less sensitive to this stimulant. © Pesticide Science Society of Japan Keywords: maize, strigolactones, germination stimulant, parasitic weeds. Maize (Zea mays) is a major host of the root parasitic weeds known as witchweeds, Striga hermonthica and S. asiatica, and has been reported to produce several strigolactones (SLs). 1,2)Among known SLs, strigol was isolated as the major Striga seed germination stimulant in maize root exudates.3) In addition to this SL, sorgomol and 5-deoxystrigol were found in maize root exudates. 4) Recently, Jamil et al. reported the detection of novel germination stimulants tentatively called SL1 and SL2 in maize root exudates based on LC-MS/MS analysis.5) SL1 and SL2 were found to have the molecular weights of 348 and 276, respectively. Herein we report the isolation and structure determination of SL2, named methyl zealactonoate, 6) and its germination stimulation activities on S. hermonthica, Phelipanche ramosa, and Orobanche minor seeds.The crude EtOAc extract (350.7 mg) of root exudates collected over 5 weeks from ca. 800 maize seedlings grown hydroponically was purified using silica gel column chromatography (CC) with stepwise elution using n-hexane and EtOAc. The 30% and 40% EtOAc fractions which were found via LC-MS analysis to contain SL1 and SL2 were combined and further purified by silica gel CC (25% EtOAc in n-hexane). Since SL1 was found to be a mixture of at least two isomers with very similar chromatographic behaviors, we focused on the purification of SL2. The fractions containing SL2 were combined and purified by HPLC on an ODS column followed by HPLC on an ODS-CN column to afford pure germination stimulant 1 (7.83 mg) as an amorphous solid.The molecular formula of 1 was established to be C 20 H 24 O 7 on the basis of protonated and sodium adduct ions obtained by HR-ESI-TOF-MS, indicative of nine degrees of unsaturation. The molecular ion observed at m/z 376 [M] + in GC-MS also supported this molecular formula.The 1 H NMR spectrum of 1 displayed two singlet methyl protons at 0.73 and 0.99 ppm, two methyl protons with small coupling (<2 Hz) at 1.25 and 1.64 ppm; one oxygenated methyl proton at 3.35 ppm; two geminal coupled methylene protons at 1.90 and 2.25 ppm, five olefinic protons at 4. 71, 4.94, 5.20, 5.53, and 7.45 ppm; and two coupled olefinic protons with 16.75 Hz, suggesting the trans olefin...

Conversion of carlactone to carlactonoic acid is a conserved function of MAX1 homologs in strigolactone biosynthesis

“…This means the ability of a plant to produce SLs is not given only by the intrinsic properties of the enzyme, but also by the availability of the substrate in the plant. Recently, zealactone (methyl zealactonoate) has been identified as a major germination stimulant of root‐parasitic plants produced by maize (Charnikhova et al ., ; Xie et al ., ). Zealactone is an MeCLA derivative having a lactone with an isopropenyl group on the A ring.…”

“…To carry out the transient expression of MAX1 homologs, N. benthamiana was used, provided by Dr Masashi Asahina (Teikyo University, Japan). To analyze SLs in root exudates, Arabidopsis atd14‐2 (Seto et al ., ) and wild‐type (Col‐0), tomato (cv MomotaroFight; Yoneyama et al ., ) and maize (cv Pioneer2817; Xie et al ., ) were used.…”

“…They are canonical SLs which can be divided into strigol‐ and orobanchol‐type SLs by stereochemical differences at the BC ring junction (Xie et al ., ; Flematti et al ., ). Recently, non‐canonical SLs which lack the A, B or C ring, such as methyl carlactonoate (MeCLA), avenaol, heliolactone and zealactone, have also been isolated (Abe et al ., ; Kim et al ., ; Ueno et al ., ; Charnikhova et al ., ; Xie et al ., ). However, it remains elusive why plants produce different SLs, what are their physiological differences and which structure is the most active form in planta .…”

Hydroxyl carlactone derivatives are predominant strigolactones inArabidopsis

“…Although it was proposed that sorgomol is produced from 5DS (Motonami et al, 2013), LBO did not produce sorgomol from 5DS (data not shown). Maize plants produce zealactone (Charnikhova et al, 2017; Xie et al, 2017) and zeapyranolactone (Charnikhova et al, 2018), non-canonical SLs with unique structures. Maize LBO did not produce these SLs from MeCLA (Data not shown).…”

Regulation of biosynthesis, perception, and functions of strigolactones for promoting arbuscular mycorrhizal symbiosis and managing root parasitic weeds

“…Because CL has an R configuration at C11 which corresponds to the 2′‐position of the D ring in canonical SLs, natural SLs have a 2′ ( R ) stereochemistry. In addition to CL, avenaol, heliolactone, zealactone, zeapyranolactone, lotuslactone, and CL‐derived compounds such as carlactonoic acid (CLA) and methyl carlactonoate (MeCLA) are typical non‐canonical SLs (Fig. ).…”