Metatranscriptomic Analysis of Pycnopodia helianthoides (Asteroidea) Affected by Sea Star Wasting Disease.

Brent M Gudenkauf,Ian Hewson,Christopher James Johnson

doi:10.1371/journal.pone.0128150

Abstract

Sea star wasting disease (SSWD) describes a suite of symptoms reported in asteroids of the North American Pacific Coast. We performed a metatranscriptomic survey of asymptomatic and symptomatic sunflower star (Pycnopodia helianthoides) body wall tissues to understand holobiont gene expression in tissues affected by SSWD. Metatranscriptomes were highly variable between replicate libraries, and most differentially expressed genes represented either transcripts of associated microorganisms (particularly Pseudomonas and Vibrio relatives) or low-level echinoderm transcripts of unknown function. However, the pattern of annotated host functional genes reflects enhanced apoptotic and tissue degradation processes and decreased energy metabolism, while signalling of death-related proteins was greater in asymptomatic and symptomatic tissues. Our results suggest that the body wall tissues of SSWD-affected asteroids may undergo structural changes during disease progression, and that they are stimulated to undergo autocatalytic cell death processes.

Highlights

Sea stars (Echinodermata: Asteroidea) are crucial components of coastal marine ecosystems, with some considered keystone species due to their disproportionately large influence on benthic community structure relative to their abundance [1]
Sea star wasting disease (SSWD) describes a suite of objective clinical signs observed in asteroids, beginning with behavioral changes including lethargy and curling of limbs, followed by development of lesions prior to arm autotomy, loss of animal turgor, and animal death
Our results suggest that body wall tissues of SSWD-affected asteroids experience enhanced tissue degradation, matrix remodeling, and decreased metabolic activity compared to asymptomatic tissues

Summary

Introduction

Sea stars (Echinodermata: Asteroidea) are crucial components of coastal marine ecosystems, with some considered keystone species due to their disproportionately large influence on benthic community structure relative to their abundance [1]. Echinoderms periodically experience massive mortality, often resulting in large ecosystem changes. A mass mortality of the herbivorous urchin Diadema antillarum in Caribbean Reefs in the early 1980s [2] dramatically altered the composition of coral reef communities [3]; Diadema antillarum has still not regained its pre-epizootic abundance[4]. Sea star wasting disease (SSWD) describes a suite of objective clinical signs observed in asteroids, beginning with behavioral changes including lethargy and curling of limbs, followed by development of lesions prior to arm autotomy, loss of animal turgor (deflation), and animal death. Previous episodes of asteroid wasting have been limited to single species in restricted

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