PhD Exit Seminar – Tauqeer Ahmad (AbouHaidar lab)

PhD Exit Seminar

Thursday January 21^st, 10:10 am – Earth Sciences Centre, Rm. 3087

Tauqeer Ahmad (AbouHaidar lab)

“Translocation of Virus-Derived Nucleic Acids to Chloroplasts and Mitochondria in Plants“

Abstract

Many studies have documented the role of transit peptides and viral proteins in targeting various viruses to specific subcellular regions of their hosts. However, knowledge hitherto about the specific sequence(s) and/or motif(s) involved in the trafficking and subcellular localization of viral RNAs and DNAs is very limited. In my thesis, I have demonstrated that a non-coding RNA sequence from potato virus X (PVX-RNA) as small as 127 nucleotides (located near the 3´end of 8 kDa and the start of CP genes as well as the non-coding intergenic region) is capable of translocating not only its own PVX-RNA sequence but also a reporter gene, GFP (green fluorescent protein) mRNA, into chloroplasts of the transgenic tobacco plants. This is the first evidence showing that a small viral RNA sequence (designated “RNA tractor”) is capable of translocating RNA sequences into the chloroplasts; however, the functional role of this mechanism remains elusive.

Begomovirus, the largest genus of the Geminiviridae family, consists of plant viruses with circular single-stranded DNA genomes. Begomoviruses infect a wide range of economically important plants. I investigated two begomoviruses on various Nicotiana species to assess the effects of their ploidy level on infectivity and symptomatology. For this purpose, infectious clones of Ageratum enation virus (AEV), a monopartite (DNA-A with Beta-satellite DNA particle) and Tomato leaf curl New Delhi virus (ToLCNDV), a bipartite (DNA-A and DNA-B), begomoviruses were used. All plants inoculated with ToLCNDV were systematically infected and showed characteristic symptoms. However, in the case of AEV, all plants except N. tabacum cv. Xanthi were infected by the virus but remained symptomless. Taken together, these results indicate that there is no clear relationship between infectivity and ploidy levels; furthermore, symptomatology depends on the type of virus and/or plant species.

Another key question to answer was whether or not the genomes of the begomoviruses could be isolated from chloroplasts of the infected tobacco and tomato plants. PCR results confirmed the presence of only DNA-A of the AEV in the chloroplasts. Preliminary studies also clearly show that the “RNA tractor” sequence and AEV genome are incapable of targeting the mitochondria. These findings suggest that members from different viral families may be associated with the same organelle, but that members do not necessarily target the different organelles. Thus, the present study could be important for understanding the evolutionary importance of the interactions of viral genomes with different organelles of plant cells and their consequential pathological effects.