Lecture 30 PMB

Question	Answer
Crown gall disease process	1) Plant wound is infected 2) A. tumefaciens attaches has a Ti plasmid 3) T-DNA contained w/in Ti plasmid 3) T-DNA transferred to cell, integrated into plant genome 4) Tumorigenesis, production of opions
Agrobacterium tumefaciens	gram negative, aerobic, rod-shaped can live on roots or in aerated soil
Through what secretion system is T-DNA transferred to plant cell genomes?	Type IV Secretion System
Crown gall disease process: Infection of the wounded plant	when plant is wounded, releases phenolic compounds --> stimulates VirA autophosphorylation --> phosphate transferred to VirG --> VirG activates vir genes --> motility reduced, cellulose fibrils + richadhesin made --> A. tumefaciens better attaches to plant
VirA	histidine kinase located on membrane of A. tumefaciens stimulated by phenolic compounds autophosphorylates and passes phosphate to VirG
VirG	transcriptional response regulator, when phosphorylated it activates tx of vir genes
Ti plasmid structure	T-DNA (oncogenes + opine synthesis genes) transmissibility genes opine catabolism genes vir genes (virulence factors)
opine molecules	used as a C & N source for A. tumefaciens T-DNA directs plant host to synthesize these for the bacterium
Crown gall disease process: Processing of the T-DNA from the Ti Plasmid	vir genes activated by VirG-P --> VirD endonuclease nicks Ti plasmid at T-DNA borders --> VirE binds single strand of T-DNA & transports to plant cell --> VirD remains bound to one end of T-DNA during transfer
Crown gall disease process: T-DNA transferred to host cell & integrated into genome	T-DNA transferred via Type IV secretion: composed of proteins VirB1-11 + VirD4 T-pilis attaches to host plant DNA polymerase produces complementary strand to ssDNA, ds T-DNA is integrated RANDOMLY into host
Crown gall disease process: Tumorigenesis and opine production	onc gene: tumor formation, alter plant growth hormones (auxin and cytokinin) ops gene: production of opines (octopine and nopaline)
Modified Ti plasmid in genetic engineering	two vectors required: take vir genes and T-DNA border sequences, remove onc and ops genes and replace with gene of interest --> can express target gene in host plant
Arabidopsis T-DNA insertion lines	created by Ti plasmids is a large collection of transposon mutants in a particular species --> speeds up genetic study of plant biology
Creation of GMOs	created from modified Ti plasmids used to express foreign/modified genes in crop species
Rhizobium-Legume Symbiosis	1) recognition of partner and rhicadhesin-mediated attachment to root hair 2) secretion of Nod factors to cause root hair curling 3) Rhizobia penetrate root hairs, multiply within infection thread 4) Bacteria move toward main root 4) Rhizobia develop into bacteroid state within root nodule, perform N2 fixation
legume infection thread	cellulose tube made by plant host, Rhizobia travel through this to main root
Nod factors	oligosaccharides that bind to specific receptors within plant cytoplasmic membrane --> root hair curling + plant cell division --> formation of mature nodule have N-acetylglucosamine backbone made by NodABC proteins, is specific to species depending on R groups
flavonoids	produced by plants, bind to NodD receptors of correct symbiont activated NodD drives tx of other nod genes --> nodABC genes synthesize Nod factors
Root nodule metabolism	bacteria gets TCA intermediates from plant photosynthesis --> creates PMF and ATP using aerobic respiration Pyruvate + CoA + Fd(ox) → Ac-CoA + CO2 + Fd(red) Using Fd(red) as donor, fixed N (glutamine and asparagine) is shared with plant
Leghemoglobin (Lb)	made by the plant --> binds O2 to keep the free oxygen tension in the root nodule low + prevent damage to nitrogenase enzyme cell still uses O2 as electron acceptor so most of it is bound to Lb
symbiosome	derived from plant cytoplasmic membrane, surrounds colony of bacteria N2 fixation occurs AFTER this forms

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	Created by Candice Young over 6 years ago