Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 10/29/2015
Publication Date: 11/24/2015
Citation: Zhao, Y., Wei, W., Davis, R.E. 2015. Recent advances in phytoplasma research: from genetic diversity and genome evolution to pathogenic redirection of plant stem cell fate. Meeting Abstract. First International Symposium on Molecular Diagnostics … Production. Trujillo, Peru, 11/26-28/ 2015.
Technical Abstract: Parasitizing phloem sieve cells and being transmitted by insects, phytoplasmas are a unique group of cell wall-less bacteria responsible for numerous plant diseases worldwide. Due to difficulties in establishing axenic culture of phytoplasmas, phenotypic characters suitable for conventional microbial characterization remain inaccessible. Currently, phytoplasma identification and differentiation are based on analyses of multiple genetic loci with varying degrees of sequence conservation. The highly conserved 16S rRNA gene has served as the backbone of phytoplasma taxonomy and classification. Thus far, 37 ‘Candidatus Phytoplasma’ species and 32 phytoplasma groups have been delineated. An interactive research tool, iPhyClassifier, has been devised to facilitate identification of known and discovery of new phytoplasmas. The tool is accessible online at http://plantpathology.ba.ars.usda.gov/cgi-bin/resource/iphyclassifier.cgi. While enormous genetic diversity exists among phytoplasmas, there are intriguing features that unite phytoplasmas. One such feature is the presence of phage-based genomic islands or sequence variable mosaics in all phytoplasma genomes studied. Repeated attacks by ancestral phages, integrations of phage genomes, and subsequent acquisitions of horizontally transferred genes have shaped the genomic islands and enabled pathogenicity. Another unifying feature is phytoplasma’s ability to induce symptoms manifesting gross changes in the pattern of plant growth and reproduction. We suggest that the symptoms are linked to derailment of plant meristem cells away from their genetically preprogrammed destiny. The outcomes of a stem cell fate modification vary depending upon the developmental stage of a meristem when it becomes affected by a phytoplasma. Reprogramming of meristem fate may represent a universal mechanism that underlies common phytoplasmal disease symptoms. Phytoplasmas have high impacts on agriculture, economy, and ecosystems. A better understanding of phytoplasma genetic diversity, evolution of pathogenicity, and phytoplasma-host interactions is essential to devising novel strategies for detection/identification of diverse phytoplasmas, and for mitigation of phytoplasmal diseases. Our research contributes to food security and attaining sustainable agricultural systems.