Opening the black box of an underexplored and megadiverse group: history, taxonomy and functionality of dark septate endophytes (DSE)

Abstract

Dark septate endophytes (DSE) are facultative, biotrophic fungi that have a close association with and are restricted to plant roots; typically, with darkly-pigmented hyphae, and which frequently produce microsclerotia within the host tissues. They do not form a single taxonomic category and are distributed across different classes, orders and families of the phylum Ascomycota, representing a highly taxonomically-diverse group. There has been greater emphasis on studying DSE that can resist abiotic stresses and which confer this ability to their host plants such as resistance to high concentrations of salts and heavy metals; conditions of low nutrient availability; and, periods of prolonged drought. Furthermore, it has been demonstrated that DSE have the potential to improve the performance of many crops, as evidenced by in vitro studies. The first observations of DSE date back over a century but, only recently, have studies focused exclusively on understanding this unique group of fungi, especially their taxonomy and functionality. This review provides a detailed history of DSE and highlights the many challenges posed by studying them. We also aim to encourage more in-depth and multidisciplinary research on DSE, particularly due to the urgent need for innovative and sustainable technologies in agriculture. DSE have shown great potential as candidates for developing future ‘bioinputs’ or ‘biologicals’.