Biosynthetic pathway and optimal conditions for the production of indole-3-acetic acid by an endophytic fungus, Colletotrichum fructicola CMU-A109

Abstract

Endophytic fungi are known to produce indole-3-acetic acid (IAA), which can stimulate plant growth. Twenty-seven isolates of endophytic fungi were isolated from Coffea arabica in northern Thailand. Only one isolate (CMU-A109) produced IAA in vitro. This isolate was identified as Colletotrichum fructicola based on morphological characteristics and molecular phylogenetic analysis of a combined five loci (internal transcribed spacer of ribosomal DNA, actin, β-tubulin 2, chitin synthase and glyceraldehyde-3-phosphate dehydrogenase genes). Identification of a fungal IAA production obtained from indole 3-acetamide (IAM) and tryptophan 2-monooxygenase activity is suggestive of IAM routed IAA biosynthesis. The highest IAA yield (1205.58±151.89 μg/mL) was obtained after 26 days of cultivation in liquid medium supplemented with 8 mg/mL L-tryptophan at 30°C. Moreover, the crude fungal IAA could stimulate coleoptile elongation of maize, rice and rye. This is the first report of IAA production by C. fructicola and its ability to produce IAA was highest when compared with previous reports on IAA produced by fungi.

Characterization of the Plant Growth-Promoting Activities of Endophytic Fungi Isolated from Sophora flavescens

“…This is in agreement with previous reports, which showed that endophytic inoculation to the host plants resulted in the improvement of growth and stress tolerance [26][27][28]. However, the elongation of rice, corn and rye coleoptile segments induced by the crude IAA extract of C. fructicola endophyte were not statistically different from those of the pure IAA treatments, but the values were significantly higher than the control (distilled water) treatment [46].…”

Biosynthetic pathway of indole-3-acetic acid in ectomycorrhizal fungi collected from northern Thailand

“…Similarly, IAA production by ECM fungi (S. sinnamariense and Suillus variegatus) and endophytic fungi (Colletotrichum fructicola, C. gloeosporioides, Tulasnella sp. and Muscodor cinnamomi) could stimulate oat and rice coleoptile elongations [29,32,[50][51][52]. IAA production from white rot fungus, Pleurotus ostreatus significantly increased the lengths of wheat coleoptile segments [53].…”

“…The crude ethyl acetate extract of the fungal indole metabolites was applied to thin layer chromatography (TLC) using silica gel G F254 aluminum (thickness 0.25 mm) plates (Merk, Germany). The plates were developed in a solvent mixture of nhexane:ethyl acetate:isopropanol:acetic acid (40:20:5:1, v/v/v/v) according to the method described by Numponsak et al [32]. Identification of indole compounds was also performed using chromogenic reagents by spraying with Ehmann's [33], Ehrlich's [33] and Salkowski's reagents on TLC plate and subsequent heating to 90˚C.…”

“…High performance liquid chromatography. IAA and related indole compound produced by fungal ECM culture were quantified using high performance liquid chromatography (HPLC) according to the method of Numponsak et al [32]. HPLC analysis was performed on a Shimadzu Prominence UFLC system, coupled to a LC-20 AD pump, using a SIL-20ACHT autosampler, CTO-20 AC column oven, CBM-20A system controller and SPD-20A photodiode array detector (Shimadzu, Japan).…”

Applications of Fungal Strains with Keratin-Degrading and Plant Growth Promoting Characteristics

“…IAA is responsible for cell division and elongation responding to various factors as light, presence of pathogens etc. Fungi are able to use secreted IAA for interaction with plants in pathogenesis or symbiotic strategies, supporting the defense mechanism of plants [47][48][49][50][51][52]. Tryptophan is the main precursor for IAA synthesis and its presence increases the IAA production which in turn, enhances the availability of substrate for plants [50].…”