More than 200 economically important plant diseases are caused by "mycoplasma-like organisms" (MLOs). These diseases affect a wide range of vegetable and fruit crops, including celery, carrots, lettuce, cherries, peaches and blueberries, causing symptoms ranging from severe yellowing to "witch's broom" to stunting and fruit loss. Up until 20 years ago, MLO-diseases were thought to be due to plant viruses, since they caused some of the symptoms of viruses, and were transmitted by insects, as are many viruses. However, electron microscopy revealed that these diseases were caused by the presence of cell wall-less bacteria in the plant vascular system. Because of their small size, pleiomorphic structure, and lack of cell walls, these organisms resemble bacterial mycoplasmas, which are animal pathogens, and hence they have been referred to as "mycoplasma- like organisms". MLOs become systemic in plants, and thus, they are able to survive over the winter in roots of infected cherry trees, blueberry bushes, or other perennials. As a result, an infected perennial plant will have chronic disease symptoms until it dies of the disease or is removed and destroyed. The only effective treatment is injection with tetracycline, but even that antibiotic causes just a remission of symptoms, without eliminating the MLO. Development of improved procedures for prevention and treatment of MLO disease would be assisted significantly by a better understanding of the disease agent. This proposal is designed to examine aspects of the physiology and membrane biology of a plant pathogenic MLO. This will provide a better understanding of the organism, including whether it shares traits of the mycoplasmas that are animal pathogens. Attempts will be made to grow the plant MLO on an artificial medium. If an MLO culture can be established, the nutritional requirements of the organism and its antibiotic sensitivities could be more thoroughly assessed. This would contribute significantly to our ability to manage and treat diseases caused by this widespread plant pathogen.
