Indole-3-Acetic Acid Is Synthesized by the Endophyte Cyanodermella asteris via a Tryptophan-Dependent and -Independent Way and Mediates the Interaction with a Non-Host Plant

Abstract

The plant hormone indole-3-acetic acid (IAA) is one of the main signals playing a role in the communication between host and endophytes. Endophytes can synthesize IAA de novo to influence the IAA homeostasis in plants. Although much is known about IAA biosynthesis in microorganisms, there is still less known about the pathway by which IAA is synthesized in fungal endophytes. The aim of this study is to examine a possible IAA biosynthesis pathway in Cyanodermella asteris. In vitro cultures of C. asteris were incubated with the IAA precursors tryptophan (Trp) and indole, as well as possible intermediates, and they were additionally treated with IAA biosynthesis inhibitors (2-mercaptobenzimidazole and yucasin DF) to elucidate possible IAA biosynthesis pathways. It was shown that (a) C. asteris synthesized IAA without adding precursors; (b) indole-3-acetonitrile (IAN), indole-3-acetamide (IAM), and indole-3-acetaldehyde (IAD) increased IAA biosynthesis; and (c) C. asteris synthesized IAA also by a Trp-independent pathway. Together with the genome information of C. asteris, the possible IAA biosynthesis pathways found can improve the understanding of IAA biosynthesis in fungal endophytes. The uptake of fungal IAA into Arabidopsis thaliana is necessary for the induction of lateral roots and other fungus-related growth phenotypes, since the application of the influx inhibitor 2-naphthoxyacetic acid (NOA) but not the efflux inhibitor N-1-naphtylphthalamic acid (NPA) were altering these parameters. In addition, the root phenotype of the mutation in an influx carrier, aux1, was partially rescued by C. asteris.

Combined Transcriptomic and Metabolomic Analysis Reveals Insights into Resistance of Arabidopsis bam3 Mutant against the Phytopathogenic Fungus Fusarium oxysporum

“…Together with other phytohormones, IAA is responsible for plant growth and development, and is involved in nearly every plant process, such as cell growth, root initiation, tropism, fruit ripening, or senescence [37]. Additionally, it plays a role in the communication between host plants and plant pathogens [37].…”

“…Together with other phytohormones, IAA is responsible for plant growth and development, and is involved in nearly every plant process, such as cell growth, root initiation, tropism, fruit ripening, or senescence [37]. Additionally, it plays a role in the communication between host plants and plant pathogens [37]. In our study, the precursor of indole-3-acetic acid (IAA), indole-3-lactic acid (ILA), had higher concentrations in mock and For-inoculated bam3 plants compared to mock wt plants at seven dpi.…”

Cork Oak Forests Soil Bacteria: Potential for Sustainable Agroforest Production

“…The combination of IAA produced by plant and bacteria should be optimal to promote plant growth and will determine whether bacteria will stimulate or suppress plant growth [ 38 ]. For example, in the particular case of primary root, relatively low levels of IAA are required to induce primary root growth and a supplementary source of bacterial IAA results in shorter main roots (e.g., [ 39 ]).…”

Silicon and soil microorganisms improve rhizospheric soil health with bacterial community, plant growth, performance and yield

“…Indole-3-acetic acid is one of the main signals in symbiotic relationship between host and endophytes. 207 Ethylene is also an important plant hormone that regulates variety of developmental and physiological functions. 208 Endophytic bacteria produce ethylene precursor enzyme 1-aminocyclopropane-1-carboxylate (ACC) deaminase.…”