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Table 1 Host factors involved in the antiviral defence against geminiviruses

From: Plant responses to geminivirus infection: guardians of the plant immunity

Host

Host factor

Function

Viral factor

Geminivirus

Precise role in defence response

References

Host defence responses

A. thaliana

SnRK1

It is a global regulator of energy metabolism during growth and stress conditions

Rep

TGMV

SnRK1 phosphorylates Ser 97 of Rep protein and interferes replication and infection

[98]

TrAP

CaLCuV

SnRK1 phosphorylates AL2 at ser 109 that delays infection process

[33]

N. benthamiana

PsbP

It is a core protein of oxygen-evolving complex that stabilizes Photosystem II

βC1

ToLCNDV/RaLCB

PsbP binds to the viral genome and reduces virus replication

[191]

N. benthamiana

ATG8

It is involved in autophagy, mediates protein degradation

βC1

CLCuMuV/CLCuMuB

ATG8 binds to βC1 and degrades via autophagy thus causes reduction in viral titre

[84]

S. lycopersicum

ATG8h

It is an autophagy factor, mediates protein degradation

Rep

TLCYnV

C1 gets exported to the cytoplasm by ATG8h and degraded which restricts viral infection

[66]

N. tabacum

RFP1

It is an E3 ligase that mediates protein ubiquitination

βC1

TYLCCNV/TYLCCNB

RFP1 interaction with βC1 leads to βC1 degradation thus reduces viral infection

[65]

S. lycopersicum

UBA1

A ubiquitin-activating enzyme, catalyses the first step in 26S proteasomal degradation pathway

TrAP

TYLCSV

Silencing of UBA1 increases viral infection. TrAP protein interacts with UBA1, thus inhibit its defensive activity

[71]

A. thaliana

EML1

A histone reader protein, represses active transcription by binding on H3K36 modification

Viral minichromosome

CaLCuV

EML1 binds to viral minichromosome and blocks transcription, therefore attenuates infection

[39]

S. lycopersicum

RPT4a

A subunit of 26S proteasome, aid in unfolding target proteins

Intergenic region

ToLCNDV

RPT4a binds to the viral intergenic region and blocks transcription

[40]

V. mungo

MAPK1

A protein kinase involved in SA mediated defence

Not known

MYMIV

It mediates defence by inducing SA responsive genes

[101]

Triticum monococcum

GRAB

A Geminivirus Rep A-Binding protein. It may have role in plant development

RepA

WDV

GRAB1 and GRAB2 bind to C-terminus of RepA and inhibit replication

[193]

N. benthamiana

NbSUMO1

A component of SUMOylation system

βC1

SyYVCV/

SyYVCB

It promotes ubiquitin mediated degradation of βC1 protein

[77]

Host

Host factor

Function

Viral factor

Geminivirus

Remarks

References

Geminivirus adaptations to host defence

N. benthamiana

HDA6

It interacts with MET1 and maintains chromatin silencing

Pre-coat protein

TYLCV

Pre-coat protein interfere with MET1 interaction to HDA6 and inhibit TGS

[38]

A. thaliana

ADK

It converts adenosine to AMP which is essential to maintain the methyl cycle during TGS and aid in the activation of SnRK1

TrAP

TGMV, BCTV

TrAP inactivates ADK and causes TGS suppression and inactivation of SnRK1 defence pathway

[34]

A. thaliana

SAHH

It catalyses the generation of methyl donor during TGS mediated methylation of viral genome

βC1

TYLCCNV/TYLCCNB

βC1 inhibits SAHH enzyme and suppress TGS

[37]

A. thaliana

BAM1

It facilitates cell to cell movement of RNAi signals

C4

TYLCV

C4 interacts with BAM1 domain and inhibits spread of silencing signals

[109]

N. benthamiana

MKK2

MPK4

Regulates defence responses by via phytohormones, ROS and defence-related gene expression during biotic stress

βC1

TYLCCNV/TYLCCNB

βC1 inhibits the kinase activity of both MKK2 and MPK4 and increases host susceptibility

[90]

A. thaliana

SnRK1

It is a global regulator of energy metabolism during growth and stress conditions

TrAP

TGMV, CaLCuV

TrAP inactivates SnRK1 and leads to enhanced susceptibility

[97]

BCTV

[98]

A. thaliana

NIKs

It undergoes reversible phosphorylation within its activation loop domain to carry out the defensive function

NSP

CaLCuV

NSP inhibits autophosphorylation of NIK and thus breaks suppression of NIK mediated global protein synthesis

[88]

A. thaliana

CSN5

It regulates SCF complex activity during ubiquitination

TrAP

TYLCV, TYLCSV

TrAP interacts with CSN5 and impairs SCF complex function thereby inhibits jasmonic acid signalling and enhanced infection

[72]

N. benthamiana

NbSUMO1

A component of SUMOylation system

βC1

SyYVCV/SyYVCB

It stabilises the βC1 protein

[77]