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*infection of plant wound by Agrobacterium and attachment
- *plant wound releases phenolic compounds- induces vir gene expression using two component system
- agrobacterium cell motility is reduced, cellulose fibrils formed to attach to plant and richadhesion protein produced
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structure of the Ti plasmid of Agrobacterium tumefaciens
- T-DNA is the only region actually transferred to the plant
- vir genes encode proteins essential for T-DNA transfer
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processing of T-DNA from Ti plasmid
- vir expression activated
- endonuclease nicks Ti plasmid next to T-DNA at T-DNA borders
- single stranded DNA binding protein binds the single strand of T-DNA and transports it into the plant cell
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transfer of T-DNA
- T4SS required for translocation of T-DNA complex into plant cell
- thought that the T-DNA travels through the T-pilus
- autoinducers promote T-DNA transfer
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integration of T-DNA into plant genome
- typically integrates into the host genome as full length T-DNA, one copy
- fairly random, higher frequency of integration into intergenic regions
- microsimilarities at insertion sites
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*tumorigenesis and production of opines
- T-DNA carries genes for tumor formation some of which synthesize or alter plant growth hormones auxin and cytokinin and production of modified amino acids called opines
- *opines are produced by the transformed plant cells and are a source of C and N for the agrobacterium
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disarmed Ti plasmid as tool
- remove genes involved in tumor formation
- have your gene of interested flanked by T-DNA borders
- ability to stably express genes of interest in plants - GMOs
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*flavonoids
- plant flavonoids induce expression of nod genes
- *component of the specificity of the Rhizobia- legume symbiosis
- activates positive transcriptional regulatory of nod genes
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*expression of nod genes
- nod genes encode proteins that produce nod factors
- nod factors:
- induce root hair curling
- trigger plant cell division
- another component of specificity
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*bacteroid
- differentiated bacteria
- nitrogen fixation occurs within it only when genes are expressed
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*leghemoglobin
- binds oxygen to keep it away from nitrogenase
- expression induced as symbiosis forms
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