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Title: A branch-inducing phytoplasma in Euphorbia pulcherrima associated with changes in expression of host genes

item Horvath, David

Submitted to: Journal of Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/29/2007
Publication Date: 8/1/2008
Citation: Nicolaisen, M., Horvath, D.P. 2008. A branch-inducing phytoplasma in Euphorbia pulcherrima associated with changes in expression of host genes. Journal of Phytopathology. 156:403-407. DOI:10.1111/j.1439-0434.2007.01372.x.

Interpretive Summary: A phytoplasma is a small intercellular bacteria that lacks cell walls. These specialized organisms infect numerous plants and animals, and can have symbiotic relationships with their host or result in disease. One phytoplasma that infects poinsettia results inn the bushy growth pattern sought by the horticultural industry. However the mechanisms by which this phytoplasma causes branching in poinsettia is not well understood. We used a combination of cDNA- differential display and cross-species microarray analysis to identify genes that were only expressed in phytoplasma infected or uninfected poinsettia. Four different genes were found to be specifically turned on or off during phytoplasma infection. One gene has similarity to a GAST-1, a gene known to be up-regulated by the growth h9ormone gibberellic acid. Another gene a-expansin, is also a known growth regulated gene. A histidine-containing phosphotransmitter was identified that likely plays a role in signal transduction. Also, a gene with no previously known function was identified as being differentially expressed in response to phytoplasma infection. This work provided additional evidence that microarrays containing genes from other euphrobia species (leafy spurge and cassava) can be useful in identifying differentially expressed genes in related members of the same plant family (Euphorbiaceae) that have considerable economic value. This work also identified genes that can be used to decipher the mechanisms by which this particular phytoplasma alters plant morphology. This last bit of information could impact development of other crop and horticultural species where branching is desirable or deleterious.

Technical Abstract: Four Euphorbia pulcherrima genes specifically regulated during phytoplasma infection have been identified using a combination of differential display of cDNA-PCR products and microarray analysis. According to BLAST searches the possible functions of the identified genes included a histidine-containing phosphotransmitter, an a-expansin, a protein with similarity to the gibberellin regulated GAST-1 and a protein with similarity to an Arabidopsis thaliana protein with unknown function.