Arbuscular mycorrhiza increase artemisinin accumulation in Artemisia annua by higher expression of key biosynthesis genes via enhanced jasmonic acid levels

Abstract

It is becoming increasingly evident that the formation of arbuscular mycorrhiza (AM) enhances secondary metabolite production in shoots. Despite mounting evidence, relatively little is known about the underlying mechanisms. This study suggests that increase in artemisinin concentration in Artemisia annua colonized by Rhizophagus intraradices is due to altered trichome density as well as transcriptional patterns that are mediated via enhanced jasmonic acid (JA) levels. Mycorrhizal (M) plants had higher JA levels in leaf tissue that may be due to induction of an allene oxidase synthase gene (AOS), encoding one of the key enzymes for JA production. Non-mycorrhizal (NM) plants were exogenously supplied with a range of methyl jasmonic acid concentrations. When leaves of NM and M plants with similar levels of endogenous JA were compared, these matched closely in terms of shoot trichome density, artemisinin concentration, and transcript profile of artemisinin biosynthesis genes. Mycorrhization increased artemisinin levels by increasing glandular trichome density and transcriptional activation of artemisinin biosynthesis genes. Transcriptional analysis of some rate-limiting enzymes of mevalonate and methyl erythritol phosphate (MEP) pathways revealed that AM increases isoprenoids by induction of the MEP pathway. A decline in artemisinin concentration in shoots of NM and M plants treated with ibuprofen (an inhibitor of JA biosynthesis) further confirmed the implication of JA in the mechanism of artemisinin production.

Ethylene Contributes to maize insect resistance1-Mediated Maize Defense against the Phloem Sap-Sucking Corn Leaf Aphid

“…To further rule out the requirement of JA in maize defense against CLA, Mp708 plants were pretreated with ibuprofen (IBU) or nordihydroguaiaretic acid (NDGA) that blocks the JA pathway, and CLA performance and mir1 expression were monitored before and after CLA infestation. Several studies have shown that the pretreatment of plants with JA inhibitors suppressed the activity of LOX, JA biosynthesis, and/or JA-dependent downstream products (Staswick et al, 1991;Oikawa et al, 2001;Zhang et al, 2009;Mandal et al, 2015). Our results also demonstrate that JA inhibitor treatment significantly suppressed the expression of LOX1 and Proteinase Inhibitor in Mp708 plants and were similar to a level found in the Tx601 maize susceptible inbred line (Supplemental Fig.…”

Terpenoids in plant and arbuscular mycorrhiza-reinforced defence against herbivorous insects

“…This was followed by a series of reports on the upregulation of DXS transcripts in mycorrhizal roots of various plants (Hans et al, 2004;Strack and Fester, 2006;Floß et al, 2008). Transcription of genes encoding DXS and DXR enzymes is upregulated by AM symbiosis and correlated with quantitative terpenoid concentration in leaves (Mandal et al, 2015a). This increase in transcription and terpenoid content has been ascribed to an increased concentration of the phytohormone jasmonic acid (Mandal et al, 2015a;Nair et al, 2015) and/or improved mineral nutrient availability (Mandal et al, 2015a), and may therefore be influenced by both nutritional and non-nutritional mechanisms (Mandal et al, 2013).…”

“…Transcription of genes encoding DXS and DXR enzymes is upregulated by AM symbiosis and correlated with quantitative terpenoid concentration in leaves (Mandal et al, 2015a). This increase in transcription and terpenoid content has been ascribed to an increased concentration of the phytohormone jasmonic acid (Mandal et al, 2015a;Nair et al, 2015) and/or improved mineral nutrient availability (Mandal et al, 2015a), and may therefore be influenced by both nutritional and non-nutritional mechanisms (Mandal et al, 2013). Results obtained so far suggest that the AM fungal-mediated increase in concentrations of terpenoids is due to enhanced production of IPP/DMAPP derived from the MEP pathway (Mandal et al, 2015a).…”

An ecological implication of glandular trichome-sequestered artemisinin: as a sink of biotic/abiotic stress-triggered singlet oxygen

“…Application of two strains of fungi, Glomus macrocarpum and Glomus fasciculatum, to field-grown A. annua also elevates artemisinin yield (Kapoor et al 2007). Colonization of A. annua by Rhizophagus intraradices that forms arbuscular mycorrhiza upregulates the expression of artemisinin biosynthesis genes and also increases artemisinin content (Mandal et al 2014).…”

“…Mycorrhization of A. annua by Rhizophagus intraradices induces allene oxidase synthase gene, which upregulates the expression of artemisinin biosynthesis genes and increase the accumulation of artemisinin. In contrast, the JA biogenesis inhibitor ibuprofen represses the accumulation of artemisinin in both non-mycorrhizal and mycorrhizal plant shoots (Mandal et al 2014). Based on the finding that artemisinin biosynthesis is JA inducible, Yu et al (2012) identified two A. annua JA-responsive transcription factors, AaERF1 and AaERF2, capable of binding to ADS and CYP71AV1 promoters.…”