Unexpected organellar locations of ESCRT machinery in Giardia intestinalis and complex evolutionary dynamics spanning the transition to parasitism in the lineage Fornicata

Shweta V Pipaliya,Rui Santos,Andrew J Roger,Corina D Wirdnam,Erina A Balmer,Dayana Salas-Leiva,Adrian B Hehl,Carmen Faso,Joel B Dacks

doi:10.1186/s12915-021-01077-2

Abstract

BackgroundComparing a parasitic lineage to its free-living relatives is a powerful way to understand how that evolutionary transition to parasitism occurred. Giardia intestinalis (Fornicata) is a leading cause of gastrointestinal disease world-wide and is famous for its unusual complement of cellular compartments, such as having peripheral vacuoles instead of typical endosomal compartments. Endocytosis plays an important role in Giardia’s pathogenesis. Endosomal sorting complexes required for transport (ESCRT) are membrane-deforming proteins associated with the late endosome/multivesicular body (MVB). MVBs are ill-defined in G. intestinalis, and roles for identified ESCRT-related proteins are not fully understood in the context of its unique endocytic system. Furthermore, components thought to be required for full ESCRT functionality have not yet been documented in this species.ResultsWe used genomic and transcriptomic data from several Fornicata species to clarify the evolutionary genome streamlining observed in Giardia, as well as to detect any divergent orthologs of the Fornicata ESCRT subunits. We observed differences in the ESCRT machinery complement between Giardia strains. Microscopy-based investigations of key components of ESCRT machinery such as GiVPS36 and GiVPS25 link them to peripheral vacuoles, highlighting these organelles as simplified MVB equivalents. Unexpectedly, we show ESCRT components associated with the endoplasmic reticulum and, for the first time, mitosomes. Finally, we identified the rare ESCRT component CHMP7 in several fornicate representatives, including Giardia and show that contrary to current understanding, CHMP7 evolved from a gene fusion of VPS25 and SNF7 domains, prior to the last eukaryotic common ancestor, over 1.5 billion years ago.ConclusionsOur findings show that ESCRT machinery in G. intestinalis is far more varied and complete than previously thought, associates to multiple cellular locations, and presents changes in ESCRT complement which pre-date adoption of a parasitic lifestyle.

Highlights

Comparing a parasitic lineage to its free-living relatives is a powerful way to understand how that evolutionary transition to parasitism occurred
Our findings show that Endosomal sorting complexes required for transport (ESCRT) machinery in G. intestinalis is far more varied and complete than previously thought, associates to multiple cellular locations, and presents changes in ESCRT complement which predate adoption of a parasitic lifestyle
ESCRT losses in Fornicata are gradual and represent a slow transition leading to parasitism To understand the extent to which the loss of ESCRT components correlates with parasitism, versus predating it, we investigated the complement encoded in the transcriptomes of free-living Carpediemonas membranifera and Carpediemonas-like organisms (CLOs) by comparative genomics (Fig. 1 and Additional Material 2Supplementary Table 1)

Summary

Introduction

Comparing a parasitic lineage to its free-living relatives is a powerful way to understand how that evolutionary transition to parasitism occurred. Endosomal sorting complexes required for transport (ESCRT) are membrane-deforming proteins associated with the late endosome/multivesicular body (MVB). The causative agent is the diplomonad Giardia intestinalis This enteric protist parasite has undergone large genome streamlining and modifications in its typical eukaryotic organelles, in its endomembrane system and the associated trafficking complement [2]. Simplification of the endocytic and secretory pathways in this organism is underlined by complete loss of several protein complexes associated with membrane trafficking such as AP3, AP4, AP5, TSET, and the protein complexes that are present are often reduced in their complement such as Rabs, Rab GEFs, SNAREs, and ARF GEFs [11,12,13,14,15]. Giardia has endocytic organelles called peripheral vacuoles (PVs) which perform bulk flow uptake of nutrients from the host environment and cargo sorting for retrograde transport [16, 17]

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