Lighting the tunnel of plant evolution: Scientists explore importance of two-pore channels in plants

Date:
May 2, 2022
Source:
Tokyo University of Science
Summary:
Two-pore ion channels are present in many eukaryotes -- both
animals and plants. While the possible involvement of these
channels in environmental stress responses have been discussed in
higher plants, their localizations and functional significance
remain largely unknown. Now, researchers have found the missing
pieces of evolutionary history of two- pore channels in a species
of liverwort.



FULL STORY ========================================================================== Two-pore channels (TPCs) are ancient ion channels present in the cells
of both animals and plants. In animals, including humans, these ion
channels play important roles in biological activities in various tissues,
such as in the brain and nervous system. All land plant species contain
TPC genes; in many higher vascular plants such as Arabidopsis thaliana (Arabidopsis) and Oryza sativa(rice), a single TPC gene is involved in
the activity of slow vacuolar (SV) channels (voltage-dependent cation
channels) along with long-distance signalling, defence, and responses to environmental stress. However, very little is known about the function
of TPC proteins in non-flowering mosses and liverworts-some of the oldest organisms on Earth.


==========================================================================
In a recent study, a team of researchers led by Prof. Kazuyuki
Kuchitsu from Tokyo University of Science, Japan, collaborated with
researchers from Maria Curie-Sklodowska University, Poland, to explore
the evolutionary and physiological significance of two-pore channels
in the non-flowering bryophyte Marchantia polymorpha. Their widely
recognized and appreciated article, which discusses this study in detail,
was first published online in December 2021 and subsequently in print in
the February issue in Plant and Cell Physiology. The article has also
been chosen as an "Editor's Choice" and "Research Highlight" article
for the journal, which has published a commentary.

M. polymorpha, or common liverwort, grows as thin, flat green sheets on
moist soil or rock, and is an extant descended from one of the earliest
plants to colonize land. M. polymorpha is a simple model organism that
has been used to analyze the common characteristics of land plants. ''We realized that the genome of M. polymorpha has three TPC homologs: MpTPC1,
2, and 3, belonging to two distinctive groups, type 1 and type 2 TPC
genes. We aimed to know what these two subgroups of TPC proteins do in
M. polymorpha,'' Prof. Kuchitsu explains.

To do so, the researchers first performed a phylogenetic analysis of the
TPC genes in the green plant lineage. Then they characterized the three
TPC proteins: MpTPC1 from the Type 1 TPC gene and MpTPC2 and MpTPC3 from
the Type 2 TPC gene. Tagging these proteins with a fluorescent marker,
they studied their localization in M. polymorpha cells. By CRISPR-Cas9
genome editing, the researchers developed mutant plants that didn't
contain functional TPC1, TPC2, or TPC3 genes and double mutant plants
that lack functions of both TPC2 and TPC3 genes. Then, by patch-clamp electrophysiology analyses, they measured the ionic currents in isolated vacuoles from the living cells of M. polymorpha plants.

The results of the phylogenetic analyses provided some intriguing insights
into the evolutionary history of M. polymorpha. "Unlike the type 1 TPC
gene, which is well conserved in all land plants, type 2 TPCs were found
in algal species.

This suggested that although the type 2 TPCs emerged before plants
colonized the land, they failed to make their way into the genome of
higher vascular plants and hornworts," Prof. Kuchitsu tells us.

The researchers also found that the three TPC proteins were primarily
localized at the vacuolar membrane of M. polymorpha. The mutant that
lacked a functional TPC1 gene showed no SV channel activity. But mutants
that lacked either functional TPC2, TPC3, or both, exhibited usual SV
channel activity. Molecules such as phosphatidylinositol-3,5-bisphosphate
and nicotinic acid adenine dinucleotide phosphate, that activate the
TPCs of mammalian cells, failed to affect the ion channel activity in
isolated vacuoles of the mutant plants.

Prof. Kuchitsu surmises, "These observations, when tied down together, indicated that the type 1 TPCs-which are ubiquitous in all land plant
species- are responsible for SV channels in their vacuolar membrane,
but the type 2 TPCs likely encode ion channels that are different from
the SV channel and animal TPCs." The team's findings provide much-needed functional and evolutionary insights into the important-yet-elusive TPC
family in plants, and on plant ion channels in general. With their eye
on future research, they also aim to use insights from the evolutionary
history of plants for improving plant growth and defence mechanisms
against biotic and abiotic stresses. This could benefit industries like agriculture, among others.

The funding for this research was obtained through a grant from Japanese Society for the Promotion of Science and the National Science Centre,
Poland.


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


========================================================================== Journal Reference:
1. Kenji Hashimoto, Mateusz Koselski, Shoko Tsuboyama, Halina
Dziubinska,
Kazimierz Trębacz, Kazuyuki Kuchitsu. Functional Analyses of
the Two Distinctive Types of Two-Pore Channels and the Slow Vacuolar
Channel in Marchantia polymorpha. Plant and Cell Physiology, 2022;
63 (2): 163 DOI: 10.1093/pcp/pcab176 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/05/220502094736.htm

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