Vir proteins suppress the host innate immune system;

农杆菌与植物互作的主要信号：phenolics (acetosyringone), aldose monosaccharides (glucose), acidic pH(～5.5) and low phosphate, 其中酚类是必需的，其它信号能增加农杆菌对酚的敏感性，扩大信号作用。

农杆菌受到植物受伤信号分子（酚类）的诱导后，通过VirA-VirG信号系统激活毒性蛋白（Vir）的表达，诱导表达产生的VirD1、VirD2、VirC1 和VirC2 形成松弛体，具有松弛酶和核酸内切酶活性的VirD2 能在特定的位点上(LB第3和4个碱基之间)把T-DNA中的一条链从Ti 质粒上切割下来，并且以共价键的形式结合在单链T-DNA(RB)的5’－端，形成VirD2-单链T-DNA－nVirE2 复合物，该复合物在VirD5, VirE2, VirE3和VirF的作用下通过由VirB 和 VirD4组成的type IV secretion system (T4SS)从细菌进入到植物细胞内，T链复合体在VirE2结合蛋白VIP1、VirE3和VirE2作用下形成超T链复合体并向细胞核靠近，到达植物细胞核后，在VIP1结合蛋白VBF和VirF的作用下，VIP1 和VirE2从复合体上解离下来，并通过蛋白酶体SCF (Skp1-Cul1-F-box protein)ubiquitin E3 ligase complex降解。

T-DNA整合到植物基因组主要是通过宿主的DNA修复机制完成的。染色体修饰在DNA修复中起着重要的作用，构成核小体的八聚体的组蛋白H2A, H2B, H3和H4的N-端尾巴容易被进行翻译后的修饰，包括磷酸化、甲基化、乙酰化和泛素化等，这些修饰与T-DNA插入有关系。

DSB诱导因子如X射线，能提高T-DNA的插入；

瞬时表达rare-cutting restriction enzyme能提高T-DNA的插入；

Gram-negative bacterium is a broad-host range plant pathogen, tumour-inducing (Ti) plasmid

transfer DNA (T-DNA),

The expression of T-DNA-encoded bacterial genes in the host cell results in the production of enzymes that catalyse the synthesis of plant hormones, which are responsible for tumour growth and the formation of novel aminoacid–sugar conjugates, termed as opines. As opines can serve as carbon and sometimes nitrogen sources for Agrobacterium to the exclusion of most other microorganisms, they provide a selective advantage for this species.

Disarmed plasmids, the genes responsible for tumourous growth have been removed, ensuring that the transformed cells can be regenerated into fertile plants that transmit the engineered DNA to their progeny

 

VirA is a membrane-bound sensor and VirG is the intracellular response regulator

On signal sensing, the histidine kinase VirA activates VirG through transferring its phosphate to a particular aspartate of VirG, thereby activating VirG to function as a transcription factor. Phosphorylated VirG then binds at specific 12 bp DNA sequences of the vir gene promoters (vir boxes), thereby activating transcription.

cells in the root elongation zone were found to be the most highly transformable (Yi et al, 2002). Cells of this non-meristematic zone are not undergoing a normal cell cycle, but endoreduplication.

Cell division activity 对转化是很重要的。

chvA, chvB, and pscA (exoC), which are involved in the synthesis and/or localisation of periplasmic b-1,2 glucan，利于农杆菌和植物附着；

soluble pectic plant cell wall fractions decreases both the specific binding of Agrobacterium to plant cells and tumour-induction frequencies。

The VirB complex belongs to the class of type IV secretion systems (T4SS), which are found across a broad range of Gram-negative bacteria and are involved in the conjugative transfer of plasmids between bacteria as well as the translocation of Vir factors from pathogens to host cells during infection。

VirB1–11 and VirD4 and is required for virulence.

 

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