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
Abeer Ahmed Khalaf
- Cairo, Egypt - Graduate PhD in PMCB
Program, UF / Post Doctorate
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.