第19回みちのくウイルス塾

植物ウイルスからみた宿主-ウイルスの相互作⽤

〜ウイルスと植物の共存と攻防〜

東北⼤学 農学研究科

⾼ 橋 英 樹

2020年7⽉23⽇（⽊）〜7⽉24⽇（⾦） 仙台医療センター・ウイルスセンター

1.  Differences and similarities of immune system between plants and animals 2. Acute infection with plant viruses 3. “Virus latency and the impact on plants”

Contents

Plants and animals are both kingdoms of living things. They differ in important aspects. The chart below summarizes some of these differences.

How Plants and Animals Differ ?

PLANTS ANIMALS

Plants are generally rooted in one place and do not move on their own.

Most animals have the ability to move fairly freely.

Plants contain chlorophyll and can make their own food

Animals cannot make their own food and are dependent on plants and other animals for food.

Plants give off oxygen and take in carbon dioxide given off by animals.

Animals give off carbon dioxide which plants need to make food and take in oxygen which they need to breathe.

Plants have either no or very basic ability to sense.

Animals have a much more highly developed sensory and nervous system.

Difference between Plant and Animal CellsPlant and animal cells are both eukaryotic cells. However, there are distinct properties between the cells found in plants and those found in animals under a light microscope. Below is a list of the major differences:

PLANTCELLS ANIMALCELLS

Hasacellwall,regularinshape Doesnothaveacellwall,irregularinshape

Chloroplastpresent Nochloroplastpresent

Largevacuoleslocatedinthecenterofthecell Smalltemporaryvacuolesornovacuole

Starchgrainspresent StarchgrainsnotpresentDuetothecentralloca=onofthevacuole,thenucleusofthecellmaybelocatedattheedgeofthecell

Thenucleusisusuallylocatedcentrally

PlantAnimal

Plants and animals were constantly invaded by pathogens. However….. Is a couple of different strategy used for defend themselves ?

Mosaic disease Chicken pox

The mechanisms of plant and animal defense system show impressive structural and strategic similarity.

Plant and Animal Defense

Pathogens

Physical barriers

PAMP-triggered immunity (PTI)

Effector-triggered immunity (ETI)

Plants

Hypersensitive Response

Animals

Vertebrates Invertebrates

Humoral response

B cells

Antigen Antibody

Cell-mediated response

Cytotoxic T cells

Infected cells

Innate immune system Plant immune system

Adaptive immune system

Plant

Phagocytes and Natural killer cells

Chondrichthyes Teleostei

Amphibia

Reptilia

Aves

Mammalia

Echinoderm

Prochordata

Agnatha

PAMP-triggered immunity (PTI)

= Virus-induced gene silencing (VIGS)

Virus induced gene silencing (VIGS) = PTI

Viral RNA

ウイルス複製酵素dsRNA (Replicative intermediate)

siRNA(21bp)siRNA(22bp)

Degradation of viral RNA

DCL2 DCL4

SDE3

RDR6

AGO

siRNA pathway

Viral RNA replicase

Phylogenetic analysis supports independent expansions of an ancient eukaryote Dicer protein in animals and plants.

Animal

Plant

PAMP-triggered immunity (PTI)

= Virus-induced gene silencing (VIGS)

Effector-triggered immunity (ETI)

= Intracellular pattern recognition

receptors (PRRs)-mediated defense system

Dr.ClaireThomas:OntheOriginsofPlantImmunity.　Originsofahistoryofbeginnings.Blogs&Communi=es.JULY21,2009.

Plants and animals to resist infection show impressive structural and strategic similarity.

Plant cellsVertebrate and Invertebrate cells

Trans-membrane pattern-recognition receptor (PRR)

LRR

TIR

Intercellular PRR Variable NBS LRR

Trans-membrane PRR

Intercellular PRR

CC NBS LRR

TIR NBS LRR

LRR

Kinase

Plant and Animal Defense

Pathogens

Physical barriers

PAMP-triggered immunity (PTI)

Effector-triggered immunity (ETI)

Plants

Hypersensitive Response

Animals

Vertebrates Invertebrates

Humoral response

B cells

Antigen Antibody

Cell-mediated response

Cytotoxic T cells

Infected cells

Innate immune system Plant immune system

Adaptive immune system

Plant

Phagocytes and Natural killer cells

Chondrichthyes Teleostei

Amphibia

Reptilia

Aves

Mammalia

Echinoderm

Prochordata

Agnatha

1.  Differences and similarities of immune system between plants and animals 2. Acute infection with plant viruses 3. “Virus latency and the impact on plants”

Contents

Virus multiplication in single cell

＋＋＋＋

Virus particle

Uncoating

Viral RNA

Replicase

(-)RNA

Coat protein synthesis

Viral RNA

Virus assembly

Cell-to-cell movement protein

Plasmodesmata

Virus induced gene silencing (VIGS) = PTI

ViralgenomeRNAViral genome RNA

Virus RNA replication

DICER

siRNA

RISC

RISC

RISC

Viral genome RNA

21-25nt small RNAs

Replicative intermediate dsRNA

Virus induced gene silencing (VIGS) = PTI

ViralgenomeRNAViral genome RNA

Viral RNA replication

DICER

siRNA

RISC

RISC

Viral genome RNA

Silencing suppressor

Silencing suppressor

RISCSilencing suppressor

Replicative intermediate dsRNA

Virus induced gene silencing (VIGS) = PTI

ViralgenomeRNAViral genome RNA

Viral RNA replication

DICER

siRNA

RISC

RISC

Viral genome RNA

Silencing suppressor

Silencing suppressor

RISCSilencing suppressor

miRNA gene

Pre-miRNA

miRNA

Target RNA： ＊Degradation ＊Translational regulation ＊DNA methylation

DICER

miRNA (21 base)

RISC

DICER

miRNA pathway

Replicative intermediate dsRNA

Cell-to-cell Movement

Leaf tissue

Long-distance movement

Mosaic symptoms

Vasculer tissue

Inoculated leaf

Non-inoculated upper leaves

Single cell Virus

Susceptible response

Specific cultivars of host plants carrying virus resistance gene can recognize viral proteins including silencing suppressor protein through intracellular immune receptor.

Trans-membrane PRR

CC NBS LRR

TIR NBS LRR

LRR

Kinase

Virus

Recognition

MAP kinase cascade

WRKY transcription factors

Defense-related gene expression

Intracellular immune receptor

Effector-triggered immunity (ETI)

Virus mutants can escape from recognition by intracellular immune receptor thereby inactivating downstream signaling.

Evolutionary arms race

Trans-membrane PRR

Intracellular immune receptor

CC NBS LRR

TIR NBS LRR

LRR

Kinase

Virus mutants

Recognition

MAP kinase cascade

WRKY transcription factors

Defense-related gene expression

In the evolution of host plants, host plant creates new intracellular immune receptor gene, which can recognize this virus mutant.

The most numerous R-gene class is represented by the gene family that encodes proteins containing a nucleotide-binding (NB) and leucine-rich repeats (LRRs) domains.

Marone et al. (2013) Int. J. Mol. Sci. 14: 7302-7326.

Nucleotide-binding site (NB)-leucine rich repeat (LRR) class R genes identified in different plant genomes.

CC/TIR domain

NB domain (ARC1) (ARC2)

LRR domain

Schematic representation of a typical NB-LRR protein

This evolutionary arms race between virus and host plants is possibly explained by fitting it to “Red Queen Hypothesis”.

“Red Queen Hypothesis”

3. “Virus latency and the impact on plants”

Contents

Agricultural ecosystem Natural ecosystem

Wild plants seem be often latently infected with viruses, but impact of latent infection on host plants is not enough to be investigated.

Arabidopsis halleri (Perennial plant)

Arabidopsis halleri and Arabidopsis thaliana

Arabidopsis thaliana(Annual plant)

https://www.ruhr-uni-bochum.de/pflaphy/Seiten_en/PG_Kraemer_e.html

After flowering, the stems fall down, and new seedlings develop from the axils. The seedlings can survive by rooting on soil.

Axils

CCA

CCA

Cap

Cap

RNA1

RNA2

CCA Cap

RNA3

1a protein

2a protein

3a protein

2b protein

coat protein (CP)

Cucumber mosaic virus strain Ho : CMV(Ho)

!  (+) single strand RNA genomes ! Host range: 1,200 species ! Strain: various isolates !  Transmission: aphid

2b gene

CMV(Ho) systemically spread in plant, but any symptoms did not develop.

Arabidopsis thaliana inoculated with CMV(Ho)

CMV (Ho)

Mock

#1 #2 #3

#1 #2 #3

#1 #2 #3

#1 #2 #3

Immunological detection of virus coat protein by press blotting

CMV (Ho)

Mock

CMV(Ho)

What is the determinant in 2b gene for latent infection with CMV(Ho)？

CCA

CCA

Cap

Cap

RNA1

RNA2

CCA Cap

RNA3 2b protein

77 106

2b protein

RNA silencing suppressor/siRNA-binding domain

Cucumber mosaic virus strain Ho (CMV-Ho)

2b

CCA

CCA

Cap

Cap

RNA1

RNA2

CCA

Cap

RNA3

1a protein

2a protein

3a protein

2b protein

coat protein (CP)

CMV(Ho) genomic RNA

Change of gene expression

pattern

Phenotypes: Tolerance to environmental stresses etc.

DNA methylation

Working hypothesis regarding the impact of virus latent infection on the life of host plants

2b

2b

Change of DNA methylation

This study was financially supported by grants for “Scientific Research on Innovative Areas” from the Ministry of Education, Culture, Science, Sports and Technology (MEXT) of Japan (Grant numbers: 16H06429, 16K21723 and 16H06435).

Acknowledgements