Epsilon Archive for Student Projects

Abstract

Autophagy is a conserved intracellular process in eukaryotes that degrades and recycles unwanted
and harmful constituents to maintain cellular homeostasis and to adapt to stressful conditions.
Autophagy has also emerged as an important part of the immune system against pathogens, such as
viruses. Research on autophagy has focused mainly on cytoplasmic processes; however, recent
studies on animals highlighted the presence and function of autophagy-related (ATG) proteins in
the nucleus. In plants, much less is known about the nuclear role of ATG proteins and their relevance
upon viral infection.
Autophagy plays a central role in the immune response against cauliflower mosaic virus
(CaMV), a pararetrovirus with a double-stranded DNA genome. However, it is still unknown
whether autophagy processes are connected to the nuclear steps of the CaMV infection cycle. A
nuclear interplay between CaMV and the plant host Arabidopsis thaliana was preliminarily
observed by the host lab: CaMV infection induces a specific isoform of the ATG8 protein family to
shape a distinct nuclear speckle in close proximity to the nucleolus, resembling Cajal bodies (CBs).
The potential connection of autophagy and CBs, which are implicated in plant stress and virus
infection responses, was further supported by the strong colocalization found between the ATG8
isoform and the CB component coilin upon transient expression in Nicotiana benthamiana leaves.
In this MSc thesis, I further investigated the possible interaction of the ATG8 isoform with CBs.
Confocal microscopic analysis revealed that the subnuclear localisation of the ATG8 isoform
occurred upon infection with CaMV CM1841 isolate as with the previously tested Cabb B-JI,
suggesting an isolate-independent response. In contrast to coilin, the CB protein U2B” did not show
specific affinity to ATG8 and remained evenly distributed in the nucleus in the N. benthamiana
system. However, the colocalization of U2B” with the viral capsid protein P4 as well as the increased
viral accumulation in the Arabidopsis U2B” loss-of-function mutant suggested a possible
contribution of U2B” to CaMV infection.