Appressorial interactions with host and their evolution

Fungi have evolved diverse strategies to acquire nutrients as endophytes, saprobes, symbionts, or pathogens. Appressoria have been intensively studied due to their importance in attaching and breaching the host surface. These specialized infection structures have evolved into various morpho-types: proto-appressoria, hyaline appressoria, melanized (dark) appressoria, and compound appressoria. In this review, we discuss the differences in the formation, differentiation, and function of appressoria among fungi with diverse life strategies. Using DNA sequence information, LSU, 5.8S, SSU and rpb2 gene fragments, we reconstructed the ancestral states for appressorial types in the main phyla of fungi and fungus-like organisms and found that the hyaline appressoria was the most ancestral form. Our analysis estimated proto-appressoria diversification during the Mesozoic period (92–239 million years ago), however, its origin remains inconclusive. Our data suggest that these hyaline appressoria diversified into melanized or compound appressoria, with evidence of adaptive radiation.