In integrated approach to increase lime tolerance to witches broom: study of host- pathogen intraction in acid lime infected by acid lime witches broom phytoplasma (candidates phytoplasma aurantifolia).

Candidatus Phytoplasma aurantifolia, the causative agent of the witches broom disease in acid lime (Citrus aurantifolia L.), is responsible for the major tree losses in Southern provinces of Iran and Oman. This pathogen is strictly biotrophic, thus completely dependent on living host cells for its survival. The molecular basis of compatibility and disease development in this system is poorly understood. Therefore, we have applied a cDNA-AFLP approach to analyze gene expression of acid lime infected by Candidatus Phytoplasma aurantifolia. We carried out cDNA-AFLP analysis on grafted infected lime of the susceptible cultivar at the representing symptoms stage. Selective amplifications with 43 primer pairs allowed the visualization of about 55 transcript-derived fragments in infected leaves, which were differentially expressed. We sequenced 51 fragments, 36 of which were identified as acid lime transcripts after homology searching. Many acid lime genes belong to various functional groups were down-regulated during infection. Acid lime homologous to known resistance genes tended to be repressed including modifier of snc1 and autophagy protein 5. Furthermore, we observed repression of formin, importin beta 3, transducin, L-asparaginase, glycerophosphoryl diester phosphodiesterase, and RNA polymerase beta. In contrast, genes encoding proline-rich protein, ubiquitin-protein ligase, phosphatidyl glycerol specific phospholipase C-like and serine/threonine-protein kinase were up-regulated during infection. The present study provides a catalogue of candidate genes possibly involved in the interactions of acid lime and Candidatus Phytoplasma aurantifolia. These results should be helpful in elucidating the molecular basis of the infection process and identify genes that could be targeted for increasing plant resistance and inhibiting the growth and reproduction of the pathogen.