Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/21/2022
Publication Date: N/A
Interpretive Summary: The Columbia Basin potato purple top (CBPPT) phytoplasma is a cell wall-less bacterium responsible for the potato purple top disease that repeatedly occurred in the Pacific Northwest region of the United States. The CBPPT phytoplasma has a broad plant host range and is capable of infecting potato, tomato, broccoli, carrot, radish, and many other vegetable crops, inflicting economic losses. In order to understand how the CBPPT phytoplasma causes diseases in host plants, ARS researchers at the Beltsville Agricultural Research Center decoded the genome of the agricultural pest. The genome information will help elucidate what pathogenic factors the CBPPT phytoplasma possesses and how these factors weaken plant defense, leading to diseases. The genome information will also help identify molecular targets for disease control. This article will be of interest to research scientists who are studying bacterial genomics, pathogen-host interactions, and molecular basis of diseases. This article will also be of interest to plant pathologists and agricultural economists who are concerned with phytoplasmal disease management.
Technical Abstract: Potato purple top (PPT) is a potato disease complex attributed to infection by phytoplasmas. Common symptoms of the disease include purple discoloration of terminal shoots and formation of arial tubers. Affected plants often wilt and die prematurely, causing substantial tuber yield and quality losses. At least five mutually distinct Candidatus Phytoplasma species have been linked to PPT disease outbreaks occurred in different geographic areas. The Columbia Basin potato purple top (CBPPT) phytoplasma is a 'Ca. Phytoplasma trifolii'-related strain and is the etiological agent responsible for the PPT epidemics repeatedly occurred in the Pacific Northwest region of the United States. The CBPPT phytoplasma is capable of infecting many vegetable crops. Studies using the CBPPT phytoplasma and its alternative host tomato as a model system have led to the discovery that phytoplasma infection can change the fate of a developing meristem, thereby altering the growth pattern and morphology of the host. As the first step toward elucidating how the CBPPT phytoplasma induces disease in its plant host, the genome of a representative strain, CBPPT1, was sequenced. The assembled draft genome of CBPPT1 consists of 78 contigs totaling 514,536 bp. A total of 559 protein-encoding genes were identified from the contigs. Among them, 442 were assigned to at least one gene ontology term, and 402 were assigned to InterPro functional categories. Despite its small size, the CBPPT1 genome possesses multiple putative pathogenicity genes homologous to those encoding virulence factors in other phytoplasmas as well as many other unknown secretory proteins. Since CBPPT phytoplasma can induce multiple mutually distinct and developmental stage-dependent symptoms in host, it is possible that the phytoplasma may deploy multiple pathogenicity factors. The draft CBPPT1 genome sequence can serve as a resource for search and eventual identification of such pathogenicity factors.