Are dark septate endophytes an ancestral ecological state in the evolutionary history of the order Chaetothyriales?

Abstract

Dark septate endophytes (DSE) are pigmented fungi that colonize plant roots. They represent a morpho-functional status composed of many species belonging to the phylum Ascomycota, distributed in different orders. The order Chaetothyriales has representatives with diverse lifestyles, among which the rock-inhabiting one has been proposed to be the ancestral ecological character state. However, all taxa have the phenotypic characteristic of being highly melanized. This trait has been considered relevant in most Chaetothyriales because it allows them to tolerate extreme or toxic environmental conditions. In the present study, aiming to reconstruct the evolutionary history of this order, we analyzed the contribution of the DSE habit to the diversification of the Chaetothyriales. We also report the distribution of the DSE habit among the main families and/or clades within the order. Our results suggest that DSE had a key position in the evolution of the order Chaetothyriales, both as an ancestral ecological character and as a character from which other specialized forms such as Domatium probably derived.