The Mechanism of Ethylene Signaling Induced by Endophytic Fungus Gilmaniella sp. AL12 Mediating Sesquiterpenoids Biosynthesis in Atractylodes lancea

Abstract

Ethylene, the first known gaseous phytohormone, is involved in plant growth, development as well as responses to environmental signals. However, limited information is available on the role of ethylene in endophytic fungi induced secondary metabolites biosynthesis. Atractylodes lancea is a traditional Chinese herb, and its quality depends on the main active compounds sesquiterpenoids. This work showed that the endophytic fungus Gilmaniella sp. AL12 induced ethylene production in Atractylodes lancea. Pre-treatment of plantlets with ethylene inhibiter aminooxyacetic acid (AOA) suppressed endophytic fungi induced accumulation of ethylene and sesquiterpenoids. Plantlets were further treated with AOA, salicylic acid (SA) biosynthesis inhibitor paclobutrazol (PAC), jasmonic acid inhibitor ibuprofen (IBU), hydrogen peroxide (H2O2) scavenger catalase (CAT), nitric oxide (NO)-specific scavenger 2-(4-Carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide potassium salt (cPTIO). With endophytic fungi inoculation, IBU or PAC did not inhibit ethylene production, and JA and SA generation were suppressed by AOA, showing that ethylene may act as an upstream signal of JA and SA pathway. With endophytic fungi inoculation, CAT or cPTIO suppressed ethylene production, and H2O2 or NO generation was not affected by 1-aminocyclopropane-1-carboxylic acid (ACC), showing that ethylene may act as a downstream signal of H2O2 and NO pathway. Then, plantlets were treated with ethylene donor ACC, JA, SA, H2O2, NO donor sodium nitroprusside (SNP). Exogenous ACC could trigger JA and SA generation, whereas exogenous JA or SA did not affect ethylene production, and the induced sesquiterpenoids accumulation triggered by ACC was partly suppressed by IBU and PAC, showing that ethylene acted as an upstream signal of JA and SA pathway. Exogenous ACC did not affect H2O2 or NO generation, whereas exogenous H2O2 and SNP induced ethylene production, and the induced sesquiterpenoids accumulation triggered by SNP or H2O2 was partly suppressed by ACC, showing that ethylene acted as a downstream signal of NO and H2O2 pathway. Taken together, this study demonstrated that ethylene is an upstream signal of JA and SA, and a downstream signal of NO and H2O2 signaling pathways, and acts as an important signal mediating sesquiterpenoids biosynthesis of Atractylodes lancea induced by the endophytic fungus.

Reactive oxygen species and hormone signaling cascades in endophytic bacterium induced essential oil accumulation in Atractylodes lancea

“…The signaling molecule solution (200 lL) was sprayed on plantlets and was allowed to flow from leaf surfaces to the roots. The chemicals and their dosages used here were selected based on previous studies, which showed that these compounds could efficiently suppress signaling molecule accumulation induced by bacterial inoculation but did not destroy normal plant ROS and hormone homeostasis Dai 2012, 2013;Ren et al 2014;Wang et al 2015a;Yuan et al 2016). Moreover, the inhibitors had no significant effects on bacterial colonization in planta, which ruled out the possibility that the suppression of essential oil accumulation was the result of reduced bacterial colonization (Fig.…”

“…Inhibitors were sprayed on plant leaves until dripping wet and a 1-day infiltration period was allowed before bacterial inoculation or application of signaling molecules (Wang et al 2011(Wang et al , 2015bDai 2012, 2013;Ren et al 2014;Yuan et al 2016). Inhibitors remaining on the leaves were washed by the addition of the bacterial suspension and allowed to flow to the plant roots.…”

“…The extraction and measurement of ethylene (ET) was conducted using a Plant Ethylene Enzyme-Linked Immunosorbent Assay Kit (Shanghai Fankel Biological Technology Co., Ltd., China) following the manufacturer's instruction (Ren et al 2014;Yuan et al 2016). Briefly, 1 g of whole plant material was ground in 10 ml ice-cold phosphate-buffered saline (pH = 7.4) and the homogenate was centrifuged at 30009g for 20 min.…”

“…Gilmaniella sp. AL12 induced essential oil accumulation in A. lancea via hydrogen peroxide (H 2 O 2 ) and hormone signaling (Ren et al 2014;Ren and Dai 2012;Wang et al 2011;Yuan et al 2016), while Acinetobacter sp. ALEB16 induced essential oil accumulation via abscisic acid (ABA) and salicylic acid (SA) signaling (Wang et al 2015b).…”

Fungal endophytes promote the accumulation of Amaryllidaceae alkaloids in Lycoris radiata

“…Actually, plant defensive responses are aroused by perceiving fungal endophytes (Camehl et al, 2010;Yuan et al, 2019). Then, the activated signalling elements, such as reactive oxygen species and phytohormones, trigger the downstream synthetic pathways of secondary metabolites in planta (Yuan et al, 2016b;Zhai et al, 2017). These bioactive secondary metabolites can regulate the growth of fungal endophytes, which help symbiotic interactions to be maintained (Liu and Reinscheid, 2004;Schulz and Boyle, 2005).…”