Agrobacterium tumefaciens is a soil bacterium in Intro to Botany that causes crown gall disease by transferring T-DNA from its Ti plasmid into plant cells. That DNA change makes infected tissue grow abnormally.
Agrobacterium tumefaciens is a plant-pathogenic bacterium that causes crown gall disease by moving a piece of its DNA into a wounded plant cell. In Intro to Botany, you usually meet it as the classic example of a bacterium that does more than just invade tissue, it actually changes the plant cell’s genetic instructions.
The key idea is the Ti plasmid, short for tumor-inducing plasmid. A section of that plasmid, called T-DNA, is copied and transferred into the plant genome. Once the plant cell starts reading those bacterial genes, it makes signals that push the cell into uncontrolled growth, which leads to the swollen gall or tumor at the infection site.
This infection usually starts at a wound. Cuts from pruning, insect feeding, or root damage give the bacterium an opening into the plant’s internal tissues. That is why crown gall shows up most often where the outer barriers of the plant have already been broken.
The bacterium is especially associated with dicotyledonous plants, which is why it comes up in plant pathology examples involving fruit trees, vines, roses, and other broadleaf plants. The visible symptoms are not just a random bump on the stem. They are the result of altered cell division and altered hormone balance caused by the transferred DNA.
Botany courses use Agrobacterium tumefaciens because it connects several plant biology ideas at once: wound response, bacterial disease, gene transfer, and plant growth regulation. It is a neat example of how a pathogen can hijack a host’s cellular machinery instead of simply consuming tissue.
This term matters because it sits right at the intersection of plant anatomy, plant pathology, and genetics. If you are learning bacterial diseases in Intro to Botany, Agrobacterium tumefaciens is the clearest example of a pathogen that changes what the plant cell does from the inside.
It also gives you a concrete model for cause and effect. A wound happens, the bacterium enters, T-DNA moves into the plant genome, and the plant forms a crown gall. That sequence is easier to remember than a vague definition of infection, and it helps you explain why some diseases create visible growths instead of leaf spots or wilting.
The term also shows up in discussions of biotechnology because the same DNA transfer system can be adapted to insert useful genes into plants. So when a class moves from disease to genetic engineering, Agrobacterium tumefaciens becomes a bridge concept, not just a pathogen name.
If your instructor asks about plant tumors, bacterial gene transfer, or why wounds make plants vulnerable, this is one of the first examples to bring up.
Keep studying Intro to Botany Unit 9
Visual cheatsheet
view galleryCrown Gall Disease
This is the disease caused by Agrobacterium tumefaciens. The bacterium triggers abnormal growths, usually at wound sites, so the disease name describes the visible symptom you see on the plant. When a question asks for the disease outcome, crown gall is the answer; when it asks for the cause, the bacterium is the answer.
Ti Plasmid
The Ti plasmid is the genetic vehicle Agrobacterium tumefaciens uses to move T-DNA into plant cells. In Botany, this is the part that connects bacterial genetics to plant disease. If you remember nothing else, remember that the plasmid carries the instructions that reprogram plant cell growth.
Gene Transfer
Agrobacterium tumefaciens is one of the best-known examples of horizontal gene transfer between a bacterium and a plant. That makes it useful for explaining how DNA can move across species boundaries. In class, this often comes up when comparing ordinary infection to a pathogen that actually alters the host genome.
breeding for resistance
Because crown gall can damage crops and ornamentals, plant breeders look for varieties that resist infection or tolerate wounds better. This connection shows the practical side of plant pathology. The bacterium is not just a textbook case, it is part of why resistant cultivars matter in agriculture and horticulture.
A quiz or short-answer question may give you a diseased stem or root and ask you to identify the pathogen type, the disease, or the infection mechanism. Your job is to connect the wound site with bacterial entry and then explain that Agrobacterium tumefaciens transfers T-DNA from its Ti plasmid into the plant genome. If a lab image shows a swollen gall, you should recognize it as crown gall disease, not a fungal mold or a nutrient deficiency. In a written response, use the sequence wound, infection, DNA transfer, tumor-like growth. That chain shows you understand how the disease develops, not just the name of the bacterium.
These are closely linked but not the same. Agrobacterium tumefaciens is the bacterium, while crown gall disease is the plant disease it causes. If a question asks for the pathogen, name the bacterium. If it asks for the symptom or disorder in the plant, name the disease.
Agrobacterium tumefaciens is a soil bacterium that causes crown gall disease in plants.
It infects plants through wounds and transfers T-DNA from its Ti plasmid into the plant genome.
The transferred DNA pushes plant cells into abnormal growth, which leads to tumor-like galls.
Botany courses use it as a classic example of bacterial plant disease and gene transfer.
The same DNA transfer system is also famous in biotechnology because scientists can adapt it to insert genes into plants.
It is a soil bacterium that causes crown gall disease by transferring T-DNA into plant cells. In Intro to Botany, you learn it as a classic example of a bacterial pathogen that changes plant growth from the inside.
It usually enters through a wound, such as a cut stem or damaged root. Once inside, it uses the Ti plasmid to move T-DNA into the plant cell, which can trigger abnormal cell division and gall formation.
No. Agrobacterium tumefaciens is the bacterium, and crown gall is the disease it causes. That distinction matters on quizzes because the organism and the symptom are different labels for different parts of the infection process.
It is a major example of bacterial plant disease, but it is also a model for gene transfer. That makes it useful both for understanding how pathogens alter plant cells and for showing how scientists can use bacteria to insert genes into plants.