Despite the prominent role ribosomes have in cellular function and the amount of research dedicated to ribosome synthesis and quality control, the mechanisms of normal rRNA turnover in eukaryotes had not been studied in any eukaryotic system. The laboratory pioneered the characterization of rRNA turnover, using the plant Arabidopsis thaliana as a model organism. We identified the main ribonuclease activity necessary for normal rRNA decay, a member of the RNase T2 family, and showed that this process is carried out in the vacuole.

We also found that components of the autophagy machinery are necessary for ribosome and/or rRNA transport to the vacuole prior to rRNA degradation, and demonstrated that general and selective autophagy mechanisms are involved in this transport. An outstanding question is why normal rRNA needs to be recycled. While more research is needed to answer this question, we found evidence suggesting that rRNA turnover is used by cells to maintain nucleotide homeostasis, and that deficient rRNA decay triggers changes in carbon flux to compensate for the reduction in activity of the nucleotide salvage pathway.

A large part of this work was done in collaboration with the laboratory of Dr. Bassham, GDCB Department at Iowa State University.

Ribosomal RNA salvage pathway in Arabidopsis.

Figure from Bassham and MacIntosh (2017) Plant Science 262, 169-174