Disentangling thermal stress responses in a reef-calcifier and its photosymbionts by shotgun proteomics

Marleen Stuhr,Laxmikanth Kollipara,Michal Kucera,Hildegard Westphal,Bernhard Blank-Landeshammer,Albert Sickmann,Claire E Reymond

doi:10.1038/s41598-018-21875-z

Abstract

The proliferation of key marine ecological engineers and carbonate producers often relies on their association with photosymbiotic algae. Evaluating stress responses of these organisms is important to predict their fate under future climate projections. Physiological approaches are limited in their ability to resolve the involved molecular mechanisms and attribute stress effects to the host or symbiont, while probing and partitioning of proteins cannot be applied in organisms where the host and symbiont are small and cannot be physically separated. Here we apply a label-free quantitative proteomics approach to detect changes of proteome composition in the diatom-bearing benthic foraminifera Amphistegina gibbosa experimentally exposed to three thermal-stress scenarios. We developed a workflow for protein extraction from less than ten specimens and simultaneously analysed host and symbiont proteomes. Despite little genomic data for the host, 1,618 proteins could be partially assembled and assigned. The proteomes revealed identical pattern of stress response among stress scenarios as that indicated by physiological measurements, but allowed identification of compartment-specific stress reactions. In the symbiont, stress-response and proteolysis-related proteins were up regulated while photosynthesis-related proteins declined. In contrast, host homeostasis was maintained through chaperone up-regulation associated with elevated proteosynthesis and proteolysis, and the host metabolism shifted to heterotrophy.

Highlights

Most marine reef-building organisms such as corals rely on symbiosis with photosynthesizing microalgae
A total of 1,618 proteins belonging to the concatenated host-symbiont database were identified by homology-driven search approaches, all of which were present in samples of all treatments and at the beginning of the experiment
The largest cluster comprised 10 protein sequences, while 926 proteins remained as single-protein clusters

Summary

Introduction

Most marine reef-building organisms such as corals rely on symbiosis with photosynthesizing microalgae. Long-term heat stress appears to affect LBF primarily by disturbing the photosynthetic performance of the symbionts[32,33,36,37], causing reduced holobiont calcification and growth[9,35,36,37] and reducing host activity[9,32] They display a marked capacity for acclimatization to short-term thermal stress events that do not induce bleaching[9] but the exact mechanisms of acclimatization and thermal stress response remain unresolved. Existing protein expression studies revealed decreases in the rate-limiting carbon fixation enzyme ribulose 1-5-biphosphate carboxylase/-oxygenase (RuBisCO)[38] and high ratios of the 70 kDa stress protein[39] in response to heat shocks These gel-based approaches can only target specific proteins, are challenging to apply to small protein volumes and do not allow partitioning between host and symbionts[24]

Methods

Results

Conclusion