The Diversity of Anti-Microbial Secondary Metabolites Produced by Fungal Endophytes: An Interdisciplinary Perspective

Walaa Kamel Mousa,Manish N Raizada

doi:10.3389/fmicb.2013.00065

Abstract

Endophytes are microbes that inhabit host plants without causing disease and are reported to be reservoirs of metabolites that combat microbes and other pathogens. Here we review diverse classes of secondary metabolites, focusing on anti-microbial compounds, synthesized by fungal endophytes including terpenoids, alkaloids, phenylpropanoids, aliphatic compounds, polyketides, and peptides from the interdisciplinary perspectives of biochemistry, genetics, fungal biology, host plant biology, human and plant pathology. Several trends were apparent. First, host plants are often investigated for endophytes when there is prior indigenous knowledge concerning human medicinal uses (e.g., Chinese herbs). However, within their native ecosystems, and where investigated, endophytes were shown to produce compounds that target pathogens of the host plant. In a few examples, both fungal endophytes and their hosts were reported to produce the same compounds. Terpenoids and polyketides are the most purified anti-microbial secondary metabolites from endophytes, while flavonoids and lignans are rare. Examples are provided where fungal genes encoding anti-microbial compounds are clustered on chromosomes. As different genera of fungi can produce the same metabolite, genetic clustering may facilitate sharing of anti-microbial secondary metabolites between fungi. We discuss gaps in the literature and how more interdisciplinary research may lead to new opportunities to develop bio-based commercial products to combat global crop and human pathogens.

Highlights

Plant pests and pathogens including viruses, bacteria, nematodes, insects, and fungi reduce crop yields by 30–50% globally, contributing to malnutrition and poverty (Pimentel, 2009)
DIRECTIONS The objective of this paper was to review the diversity of secondary metabolites with anti-microbial activities produced by endophytic fungi, from the interdisciplinary perspectives of biochemistry, genetics, fungal biology, host plant biology, human and plant pathology
With respect to fungal biology, a complexity of this field of study is that fungi can exist in both sexual and asexual forms and can sometimes switch between endophytic and pathogenic lifestyles (e.g., N. typhnium/E. typhina), with each type potentially producing different classes of secondary metabolites

Summary

INTRODUCTION

Plant pests and pathogens including viruses, bacteria, nematodes, insects, and fungi reduce crop yields by 30–50% globally, contributing to malnutrition and poverty (Pimentel, 2009). Nematodes are considered significant problems in tropical and subtropical regions, but are often undiagnosed because they exert their damage on plant roots (Shurtleff and Averre, 2000) Nematodes such as those belonging to the genera Paratrichodorus and Trichodorus are vectors of plant pathogenic viruses (Boutsika et al, 2004). Other serious fungal pathogens of crops include: Magnaporthe grisea and Pyricularia oryzae, which cause rice blast diseases in Asia; Puccinia sp., the causal agents of rusts in barley, maize, and wheat; Phytophthora infestans, an oomycete fungus which infects the Solanaceae family and led to the potato blight in Ireland in the 1840s; and Rhizoctonia solani, the causal agent of damping-off in diverse crops and stem canker in potato (Strange and Scott, 2005). Endophytes are microorganisms which inhabit plants in the tissues beneath www.frontiersin.org

Mousa and Raizada

CONCLUSION AND FUTURE DIRECTIONS