Transgenic grapefruit plants resistant to Citrus tristeza virus (CTV)
Vicente Febres – Caracas, Venezuela – Graduate PhD in Plant Pathology, UF / Post Doctorate
Grapefruit (Citrus paradisi Macf) plants were independently transformed with several regions of the CTV genome, including the RNA-dependent RNA polymerase (RdRp), translatable and untranslatable versions of the capsid protein (CP) from mild, severe and stem pitting isolates and the 3’ end (3END) in sense (S) or antisense (AS) orientation. Regenerated transgenic plants were multiplied by grafting on Swingle Citrumelo (Poncirus trifoliata X C. paradisi) rootstock and were subsequently inoculated with ‘blind’ buds from plants infected with CTV. Infection of the transgenic plants was evaluated over a 3 year period using ELISA and RT-PCR. The most resistant lines were derived from the 3’ end construct. These plants exhibited undetectable levels of the virus and no accumulation of transgene mRNA or siRNAs. In contrast, less resistant lines exhibited various levels of virus, transgene mRNA and siRNA accumulation. The methylation levels of the promoters in susceptible and resistant plants were also evaluated. Taken together our data suggest that high levels of resistance are associated with transcriptionally silenced transgenes. Also, the 3’ end of the virus is more effective in producing completely resistant transgenic plants.
Identification of genes induced in Fortunella margarita following infection with Xanthomonas axonopodis
Citrus canker disease, caused by a bacterial pathogen Xanthomonas axonopodis pv citri, affects a variety of citrus species and citrus relatives in many areas of the world. In the United States, it poses a serious threat to juice fruit production and fresh fruit industries . It continues to spread in Florida, in spite of all the efforts and millions of dollars spent annually on prevention, quarantines, eradication programs, and disease control. Kumquats (Fortunella spp.) display an apparent resistance to canker, of which the genetic mechanism has not yet been unraveled. In this study, resistance of Nagami kumquat (Fortunella margarita) was confirmed using bacterial growth curves and ion leakage experiments. Forward and reverse subtractive cDNA libraries were constructed using Nagami kumquat mRNA to identify genes that are differentially expressed during the interaction with the canker pathogen. Some clones were selected for sequencing, and the sequences were analyzed using NCBI BLAST. Homologues to known transcription factors, receptors, and resistance genes were identified. The differential expression of some of these genes was confirmed using northern and reverse northern analysis.