
f Metarhizium robertsii produces indole-3-acetic acid, which promotes root growth in Arabidopsis and enhances virulence to insects
- Authors: Xinggang Liao1 , Brian Lovett2 , Weiguo Fang3 , Raymond J. St Leger2
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- VIEW AFFILIATIONS
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1 1College of Chemistry and Life Sciences, Guizhou Education University, Guiyang, Guizhou 550018, PR China 2 2Department of Entomology, University of Maryland, College Park, MD 20742, USA 3 3Institute of Microbiology, College of Life Sciences, Zhejiang University, Hangzhou, Zhejiang 310058, PR China
- *Correspondence: Xinggang Liao, [email protected] Raymond J. St Leger, [email protected]
- First Published Online: 15 July 2017, Microbiology 163: 980-991, doi: 10.1099/mic.0.000494
- Subject: Host-Microbe Interaction
- Received:
- Accepted:
- Cover date:




Metarhizium robertsii produces indole-3-acetic acid, which promotes root growth in Arabidopsis and enhances virulence to insects, Page 1 of 1
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The plant root colonizing insect-pathogenic fungus Metarhizium robertsii has been shown to boost plant growth, but little is known about the responsible mechanisms. Here we show that M. robertsii promotes lateral root growth and root hair development of Arabidopsis seedlings in part through an auxin [indole-3-acetic acid (IAA)]-dependent mechanism. M. robertsii, or its auxin-containing culture filtrate promoted root proliferation, activated IAA-regulated gene expression and rescued the root hair defect of the IAA-deficient rhd6 Arabidopsis mutant. Substrate feeding assays suggest that M. robertsii possesses tryptamine (TAM) and indole-3-acetamide tryptophan (Trp)-dependent auxin biosynthetic pathways. Deletion of Mrtdc impaired M. robertsii IAA production by blocking conversion of Trp to TAM but the reduction was not sufficient to affect plant growth enhancement. We also show that M. robertsii secretes IAA on insect cuticle. ∆Mrtdc produced fewer infection structures and was less virulent to insects than the wild-type, whereas M. robertsii spores harvested from culture media containing IAA were more virulent. Furthermore, exogenous application of IAA increased appressorial formation and virulence. Together, these results suggest that auxins play an important role in the ability of M. robertsii to promote plant growth, and the endogenous pathways for IAA production may also be involved in regulating entomopathogenicity. Auxins were also produced by other Metarhizium species and the endophytic insect pathogen Beauveria bassiana suggesting that interplay between plant- and fungal-derived auxins has important implications for plant–microbe–insect interactions.
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Five supplementary tables and six supplementary figures are available with the online Supplementary Material.
- Keyword(s): virulence, auxin, plant-associated microbes, interaction, Metarhizium
© 2017 The Authors
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