Knock-knock? Who's there? How coral let symbiotic algae in
Solution to longstanding marine science mystery could aid coral
conservation

Date:
June 17, 2020
Source:
Carnegie Institution for Science
Summary:
Biologists have solved a longstanding marine science mystery
that could aid coral conservation. The researchers identified
the type of cell that enables a soft coral to recognize and take
up the photosynthetic algae with which it maintains a symbiotic
relationship, as well as the genes responsible for this transaction.



FULL STORY ==========================================================================
New work from a team of Carnegie cell, genomic and developmental
biologists solves a longstanding marine science mystery that could aid
coral conservation.

The researchers identified the type of cell that enables a soft coral to recognize and take up the photosynthetic algae with which it maintains
a symbiotic relationship, as well as the genes responsible for this transaction.


========================================================================== Their breakthrough research is published in Nature.

Corals are marine invertebrates that build large exoskeletons from which
reefs are constructed. But this architecture is only possible because
of a mutually beneficial relationship between the coral and various
species of single-celled algae called dinoflagellates that live inside individual coral cells.

"For years, researchers have been trying to determine the mechanism by
which the coral host is able to recognize the algal species with which
is compatible -- as well as to reject other, less-desirable species
-- and then to ingest and maintain them in a symbiotic arrangement,"
explained Carnegie Embryology Director Yixian Zheng who, with colleagues Chen-ming Fan, Minjie Hu, and Xiaobin Zheng, conducted this research.

These dinoflagellates are photosynthetic, which means that, like plants,
they can convert the Sun's energy into chemical energy. An alga will
share the sugars it synthesizes with its coral host, which in turn
provides the alga with the inorganic carbon building blocks it needs,
as well as phosphorus, nitrate, and sulfur.

"However, ocean warming due to climate change is causing many coral
hosts to lose their algal tenants -- along with the nutrients that
they provide -- a phenomenon called bleaching," explained lead author
Hu. "Without algae there to increase its food supply, the coral can
die. This makes it particularly critical to understand the symbiotic
mechanism now, as coral communities are increasingly jeopardized."
Building on Carnegie biologists' longstanding tradition of using a
model organism approach to study complicated biological processes, the
research team set out to use the pulsing, feathery, lavender-colored,
soft coral Xenia to reveal the cell types and pathways that orchestrate
the symbiotic relationship between a coral and its algae. This knowledge
can then be applied to increase our understanding of other coral species
and allow for further research into how these fragile ecosystems are
threatened by warming oceans.

Applying a wide range of genomic, bioinformatic, and developmental
biology tools, the researchers identified the type of cell that is
required for the symbiotic relationship to occur. They discovered that
it expresses a distinct set of genes, which enable it to identify,
"swallow," and maintain an alga in a specialized compartment, as well
as to prevent the alga from being attacked by its immune system as a
foreign invader. Furthermore, the researchers showed that the uptake
process occurs over five stages, with stage three representing mature, alga-hosting cells, and stage one being pre-symbiotic-relationship and
stage five being post-alga-expulsion.

Looking ahead, the team wants to understand how environmental stress
affects progression through the five stages, and which stage is most
crucial for recovery after a bleaching event, and the genes that function
at each stage.

Earlier this year, Zheng was selected as one of 15 scientists awarded
a grant from the Gordon and Betty Moore Foundation to support research
on symbiosis in aquatic systems. The foundation launched its Symbiosis
in Aquatic Systems Initiative last year. Current and emerging leaders
in aquatic symbiosis research -- as well as scientists who will apply
their deep expertise from other areas of science to aquatic symbiosis --
were selected from a competitive pool.

"Dr. Zheng's work using the soft coral, Xenia, is an exemplar of how model systems research can advance our understanding of fundamental processes in nature. We look forward to continued discovery as part of her Symbiosis in Aquatic Systems Initiative investigator award," Said Dr. Sara J. Bender, program officer, Science Program, Gordon and Betty Moore Foundation.


========================================================================== Story Source: Materials provided by
Carnegie_Institution_for_Science. Note: Content may be edited for style
and length.


========================================================================== Journal Reference:
1. Minjie Hu, Xiaobin Zheng, Chen-Ming Fan, Yixian Zheng. Lineage
dynamics
of the endosymbiotic cell type in the soft coral Xenia. Nature,
2020; DOI: 10.1038/s41586-020-2385-7 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/06/200617150019.htm

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