Genes on T-DNA
The T-DNA contains two groups of genes, which possess the ability to express in plants as follows-

• Oncogenes for synthesis of auxins and cytokinins (phytohormones). The over-production of phytohormones lead to proliferation of callus or tumour formation.
  
  
• Opine synthesizing genes for the synthesis of opines (a product from amino acids and sugars secreted by the crown gall infected cells and utilized by A. tumefaciens as carbon and nitrogen sources). Thus opines act as source of nutrient for bacterial growth, e.g. Octopine, Nopaline.

The functions of T-DNA genes are listed in the Table 5-4.2.1.

Gene	Product	Function
ocs	Octopine synthase	Opine synthesis
nos	Nopaline synthase	Opine synthesis
trns1 (iaaH, auxA)	Tryptophan-2-mono-oxygenase	Auxin synthesis
trns2 (iaaM, auxB)	Indoleacetamide hydrolase	Auxin synthesis
trnr (ipt, cyt)	Isopentyltransferase	Cytokinin synthesis
trnL	Unknown	Unknown, mutations affect tumor size
frs	Fructopine synthase	Opine synthesis
mas	Mannopine synthase	Opine synthesis
ags	Agropine synthase	Opine synthesis

Table 5-4.2.1: Function of various T-DNA genes

T- DNA:Border Sequences

• T-regions are defined by direct repeats known as T-DNA border sequences (Right and Left Border i.e. RB and LB of 25 bp each).
  
  
• These are not transferred intact to the plant genome, but are involved in the transfer process.
  
  
• The RB is rather precise, but the LB can vary by about 100 nucleotides.
  
  
• Deletion of the RB repeat abolishes T-DNA transfer, but the LB seems to be non-essential. The LB repeat has little transfer activity alone.