Function of Vir genes

The genes responsible for the transfer of the T-DNA region into the host plant are also situated on the Ti plasmid in a region of approximately 40 kb outside the T-DNA, known as the vir (virulence) region. The genes of vir region are not transferred themselves; they only induce the transfer of T-DNA.

These genes have following functions:

Vir genes	Functions
VirA	Encodes acetosyringone (phenolic sensor) receptor protein, functions as autokinase; also activates VirG gene by phosphorylation leading to constitutive expression of all genes
VirB1-B11	Encodes membrane protein, involved in conjugal tube formation through which T-DNA is transport, VirB11 has ATPase activity
VirC	Encodes helicase enzymes, binds to the overdrive region, unwinding of T-DNA
VirD1	Topoisomerase activity- required for T-DNA processing, modulates VirD2 activity
VirD2	VirD2 is an endonuclease- nicks the right border of T-DNA, directs T-DNA through the VirB/VirD4 transfer apparatus, contain nuclear localization sequences (NLS) that promote nuclear uptake of the T-complex
VirD4	Components of transfer apparatus
VirE1	Required for VirE2 export from Agrobacterium
VirE2	Single strand binding protein (SSBP), binds to T-DNA during transfer, forms a membrane channel that transfers the T-strand through the plant plasma membrane, involved in nuclear targeting and passage through nuclear pore complex, contain nuclear localization sequences (NLS), assist nuclear uptake of the T-complex by keeping the T-strand in an unfolded state
VirF	Directs protein coating of T-DNA complex removal by proteasomal machinery
VirG	Master controller DNA binding protein, vir A activates vir G by phosphorylation, vir G dimerises and activates constitutive expression of all vir operons
VirJ	T-DNA export

Some compounds that use as herbicides

S.No.	Chemical compound	How it interferes	Mechanism
1.	DCMU (3-(3,4-dichlorophenyl)-1,1-dimethylurea)	Inhibition of electron transfer	Competes with plasoquinone (QB) for binding site in PSII
2.	FCCP (cyanide-p-trifluoromethoxyphenylhydrazone;)	Uncoupling of phosphorylation from electron transfer	Hydrophobic proton carriers
3.	DNP(2,4-dinitrophenol)		Hydrophobic proton carriers
4.	Valinomycin		K+ ionophore
5.	Thermogenin		In brown adipose tissue, forms proton-conducting pores in inner mitochondrial membrane
6.	Atractyloside	Inhibition of ATP-ADP exchange	Inhibits adenine nucleotide translocase
7.	DCCD(dicyclohexylcarbodiimide)	Inhibition of ATP synthase	Blocks proton flow through Fo and CFo
8.	Aurovertin		Inhibits F1
9.	Oligomycin		inhibits Fo and CFo
10.	Venturicidin
11.	Cyanide	Inhibition of electron transfer	Inhibit cytochrome oxidase
12.	Carbon monoxide
13.	Antimycin A		Blocks electron transfer from cytochrome b to cytochrome c1
14.	Myxothiazol		Prevent electron transfer from Fe-S center to ubiquinone
15.	Rotenone
16.	Amytal
17.	Piericidin A

Source: Lehninger Principles of Biochemistry (Nelson and Cox, 6^th edition)