Plant-Pathogen Interaction - Plant Diseases caused by pathogenic bacteria, fungi and virus Bacterial Pathogenesis (Pseudomonas syringae) Plant Defenses :Preformed and inducible defenses Experimental Approaches In this talk, I’ll introduce the type of plant diseases cause by pathogenic bacteria, fungi, and virus. secondly, I’m going to talk more detail about bacterial pathogenesis: What is the general mechanisms to cause disease in infection of host. Among many bacterial pathogen, I’ll focused on Pseudomonas syringae. Although plant pathogen cuse serious damage to plants in infection, plants defend themselves against infection of pathogens. There are two kinds of plant defenses I’m going to talk; preformed and inducible defenses. Finally, I’ll show you the several experimental techniques to infect and measure growth of the pathogen.

Disease is the disfunction of normal physiological processes in plants caused by microorganisms or an abiotic factor Pathogenesis: process of infection, colonization, and pathogen reproduction Virulent pathogens : cause disease - Avirulent pathogens: do not cause disease In this siled, I want to give you some definitions related to plant pathogenesis. We can say that plant disease.. In respect of pathogen, pathogenesis indicate the process of infection,.. Not all pathogens cause disease. As I write here, in case of some pathogens that cause disease to specific host, we can say that these pathogens are virulent. If they can’t cause disease, these pathogens as avirulent.

Plant Leaf Structure Before having the discussion about infection process of pathogens to plant, I want to show you first plant leaf structure. As you can see here, leaf surface is coated by cuticle structure. Below that , we can find the epidermis cells, as one of interesting structure, we can find the stoma and guard cell. Mostly found in the lower leaf, stoma is tiny opening pore and used for gas exchange. Guard cell control the opening of stoma. Inside leaf, we can see the two tissue; xylem and phloem. Xylem transport most water and phloem transport the nutrient.

Entry of Plant Pathogens Here is one picture which generally describes entry of different plant pathogens. Outside leaf structure can be damaged by several reasons. Using wound area, most virus and agrobacterium and some fungi can infect to inside plant leaf. Some bacteria and fungi use natural opening structure such as lenticles and stoma which I showed in previous slide. As another interesting infection process, there is direct penetration caused by some of fungal pathogen like powdery mildews and rice blast. These fungi use specific structure like penetration peg which make hole on leaf surface with tremendous pressure. Lenticels : pongy areas in the corky surface of plant

Plant Disease-Bacteria Now I want to give you some examples of plant diseases caused by bacteria, fungi, and virus pathogens. This pictures show the disease caused by bacteria. Different bacteria species case different type of disease. I will show you specific mechanisms how bacteria induce these disease in later. Among this, you might interests about the formation of crown gall by Agrobacterium. As I said, Agrobacterium enter the plants through the wounds. After bacteria attaches to the wounded area, bacteria transfer tumor inducing genetic material into plant genome. Plant cells continuously express this foreign genetic material as its own. As a result, these big gall is formed. Actually, these galls interfere with water and nutrient transport.

Plant Disease-Fungi These are several plant diseses cause by fungal. You can see lots of sporulation on the surface. As you can see here, fungi usually grow in filamentous structure and lots of spore in the infection cycle.

Plant Disease-Virus These are disease types by virus.

Crop diseases restrict food production Most important pathogens are fungi or oomycetes Potato late blight- 15 sprays/summer Black Sigatoka of banana- 40 sprays/yr Mycosphaerella of wheat Wheat stem rust- Ug99 Wheat/maize fusarium head blight Grapevine downy/powdery mildew Discoveries in the last 15 years enable faster discovery and deployment of resistance The SL will devote resources to diseases of important crops; TSL+ There are diseases out there that are remarkably destructive when left unchecked- example of potato late blight which can wipe out a field in a week

Understanding plant disease and resistance is important for security and sustainability Many $B losses every year Widespread agrochemical use for weed, disease and pest control ($28B/yr) Genetic control is better than chemical control: -less risk of chemical “collateral damage” -less risk of poisoning farm workers -less labour -less fuel consumption and CO2 emissions -less use of agricultural machinery -less soil compaction -less waste of water -less costs, more yield = more farm income Genetic intervention requires knowledge

Immune Systems of Plants vs. Animals -Animals have a number of ways to Defend themselves by specialized Cells Animals also have system to distinguish between “self and non-self” I want to turn to the plant defense response against infection of pathogen. First, when we think about the animal defense systems, as you know, animals have specialized cells to defend themselves. These cells include macrophage, T-cell and B-cell and so on. Also animals have system to distinguish between self and non-self. What about plants? Macrophage ingests bacteria What about plants?

Model plant; Arabidopsis thaliana -Plants can not move to change the environment -Plants are continuously exposed to microorganisms -Plants must continuously defend themselves two types of defense 1. Preformed 2. Induced defense Each plant cell possesses these defense capacities (not by specialized cells) As you know, plants can not move their own position. Therefore, plants …. Because of this reason. Plants must continuously defend themselves and have two types of defense systems; preformed and induced defense. In contrast to specialized existed in animal, each cell of plant possesses these defense capacities. Here I put the one plant picture , Arabidopsis thaliana. This plant is used as good research model plant because genome size of this plant is small and genome is already sequenced and also life cycle is short compared to other plants. Model plant; Arabidopsis thaliana

Can Plants Be Immunized? In animal defense system, there is recognition, response, and memory. In plant defense system, we also checked that there are recognition and response. But we can make one question, there is also memory function for plant defense?