Host-Synthesized Secondary Compounds Influence the In Vitro Interactions between Fungal Endophytes of Maize

Abstract

Maize produces a suite of allelopathic secondary metabolites, the benzoxazinoids. 2,4-Dihydroxy-7-methoxy-2H-1,4-benzoxazin-3-one and 2,4-dihydroxy-2H-1,4-benzoxazin-3-one reside as glucosides in plant tissue and spontaneously degrade to 6-methoxy-2-benzoxazolinone (MBOA) and 2-benzoxazolinone (BOA) upon plant cell disruption. Several maize-associated fungi in the genus Fusarium can metabolize MBOA and BOA. BOA tolerance levels in 10 species of Fusarium and in the maize endophytes Nigrospora oryzae, Acremonium zeae, and Periconia macrospinosa were characterized. BOA tolerance ranged from 0.25 to 1.10 mg/ml among species. The influence of substrate alteration by one species on the subsequent growth of another species was assessed in the presence and absence of BOA. The colony area of the secondary colonizer in heterospecific interactions was compared to that in autospecific interactions (one isolate follows itself). In the presence of BOA, four of six secondary colonizers had greater growth (facilitation) when primary colonizers had higher BOA tolerance than the secondary colonizer. When the primary colonizer had lower tolerance than the secondary, three of six secondary colonizers were inhibited (competition) and three not significantly affected. In BOA-free medium, the number of isolates that were facilitated or inhibited was the same regardless of the tolerance level of the primary colonizer. Two of six secondary colonizers were facilitated, two inhibited, and two not significantly affected. This study provides some support for facilitation in stressful conditions under the Menge-Sutherland model. The results are not consistent with the corresponding prediction of competition in the absence of stress. The hypothesis drawn from these data is that in the presence of a toxin, fungal species that detoxify their substrate can enhance the colonization rate of less tolerant fungi.

Plants and endophytes: equal partners in secondary metabolite production?

“…The toxic compounds are present in a glycosylated form, while deglycosylation leads to a non-toxic metabolite. Therefore, enzymatic deglycosylation will result in tolerant microorganisms, if they have the respective enzyme (Saunders and Kohn 2008). In this study it was also observed that fungi, which can degrade the toxic conpounds, can lead the way for colonization by other, not so tolerant endophytes.…”

In vitro interactions between Fusarium verticillioides and Ustilago maydis through real-time PCR and metabolic profiling

“…While the functional roles of endophytes are understudied, they may act as defensive mutualists by conferring increased tolerance to pathogens (Arnold et al, 2003;Lee et al, 2009) or conferring competitive abilities to the host (Clay and Holah, 1999;Wilson, 1995). While effects on the host have been explored to some extent, mechanisms of interaction among plant-associated microbes have only been studied recently (Saunders and Kohn, 2008). Here, we develop methods to evaluate mechanisms and outcomes of interactions between two fungi commonly found in maize; the endophyte Fusarium verticillioides and the pathogen Ustilago maydis.…”

“…Interactions among microbes, including the endophytes, encompass antagonistic or competitive, facilitative, and apparently neutral outcomes (Mazurier et al, 2009;Saunders and Kohn, 2008;Pan and May, 2009). Interacting fungi may limit each other's growth through antibiosis, where secondary compounds limit mycelial growth, spore production or spore germination of the opposing fungi (Altomare et al, 2000;Goodman and Burpee, 1991;Nicoletti et al, 2004).…”

In Vitro Antifungal Activity of Different Plant Hormones on the Growth and Toxicity of Nigrospora Spp. on Date Palm (Phoenix dactylifera L.)

“…Abass et al [28 -30] isolated and identified these two species from heavily infected date palm leaves with leaf spot disease. In addition to date palm, several other important plants have been reported as a host for N. oryzae including rice and maize disease [32,33]. Recently, a growing number of researches proved the ability of N. oryzae to invade different plants such as kentucky bluegrass (Poa pratensis L.); sesame (Sesamum indicum L.) and wheat (Triticum aestivum L.) [34 -36].…”