Planting parasites: Unveiling common molecular mechanisms of parasitism
and grafting

Date:
October 10, 2020
Source:
Nagoya University
Summary:
Using the model Orobanchaceae parasitic plant Phtheirospermum
japonicum, scientists have discerned the molecular mechanisms
underlying plant parasitism and cross-species grafting, pinpointing
one specific enzyme.

Targeting this enzyme may help control plant parasitism in crops.



FULL STORY ========================================================================== Using the model Orobanchaceae parasitic plant Phtheirospermum japonicum, scientists from Nagoya University and other research institutes from
Japan have discerned the molecular mechanisms underlying plant parasitism
and cross- species grafting, pinpointing enzyme b-1,4-glucanase (GH9B3)
as an important contributor to both phenomena. Targeting this enzyme
may help control plant parasitism in crops. Also, this mechanism can be exploited for novel cross- species grafting techniques to realize the
goal of sustainable agricultural technologies.


========================================================================== Plant parasitism is a phenomenon by which the parasite plant latches onto
and absorbs water and nutrients from a second host plant, with the help
of a specialized organ called the "haustorium." Once the haustorium forms, specific enzymes then help in forming a connection between the tissues of
the parasite and host plants, known as a "xylem bridge," which facilitates
the transport of water and nutrients from the host to the parasite.

A similar mechanism is involved in the process of artificial stem
grafting, during which, the cell walls of the two different plant tissues
at the graft junction become thinner and compressed, a phenomenon made
possible by specific cell wall modifying enzymes. Cell wall modification
has also been implicated to play a role in parasitism in different
lineages of parasitic plants.

Therefore, the research team, led by Dr Ken-ichi Kurotani of Nagoya
University, hypothesized that similar genes and enzymes should be involved
in the process of parasitism and cross-species grafting. "To investigate molecular events involved in cell-cell adhesion between P. japonicum and
the host plant, we analyzed the transcriptome for P. japonicum-Arabidopsis parasitism and P.

japonicum-Arabidopsis grafting," reports Dr Kurotani. When a gene
in a cell is activated, it produces an RNA "transcript" that is then
translated into an active protein, which is then used by the cell to
perform various activities. A "transcriptome" is the complete set of
RNA transcripts that the genome of an organism produces under various
diverse conditions. The findings of their experiments are published in
Nature's Communications Biology.

Comparison of the parasitism and graft transcriptomes revealed that
genes associated with wound healing, cell division, DNA replication,
and RNA synthesis were highly upregulated during both events, indicating
active cell proliferation at both the haustorium and graft interface.

"What's more, we found an overlap between the transcriptome data from
this study and that from grafting between Nicotiana and Arabidopsis,
another angiosperm," reports Dr Michitaka Notaguchi, the co-corresponding author of the study. Glycosyl hydrolases are enzymes that specifically
target the breakdown of cellulose, the primary component of plant cell
walls. A b-1,4-glucanase identified in P. japonicum belongs to the
glycosyl hydrolase 9B3 (GH9B3) family; an enzyme from the same family
was recognized to be crucial for cell- cell adhesion in Nicotiana by Dr Notaguchi's group.

Further experiments showed that GH9B3-silenced P. japonicum could form
the haustorium with Arabidopsis but could not form a functional xylem
bridge, meaning that the P. japonicum b-1,4-glucanase is integral for the plant's parasitic activity. Further, high GH9B3 RNA transcript levels were observed during artificial grafting experiments, thereby proving that the enzyme plays an integral role in both parasitism and grafting mechanisms.

The transcriptome data generated in this study can be used to unearth additional genes and enzymes involved in plant parasitism. Additionally, further research along these directions will help scientists develop
specific molecular approaches to arrive at sustainable cross-species
grafting alternatives.


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


========================================================================== Journal Reference:
1. Ken-ichi Kurotani, Takanori Wakatake, Yasunori Ichihashi, Koji
Okayasu,
Yu Sawai, Satoshi Ogawa, Songkui Cui, Takamasa Suzuki, Ken Shirasu,
Michitaka Notaguchi. Host-parasite tissue adhesion by a secreted
type of b-1,4-glucanase in the parasitic plant Phtheirospermum
japonicum.

Communications Biology, 2020; 3 (1) DOI: 10.1038/s42003-020-01143-5 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/10/201010135507.htm

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