Conservation of rRNA decay mechanisms in eukaryotes

Given the universality of ribosomes and the almost absolute conservation of the RNase T2 family in eukaryotes, we hypothesized that the mechanism of rRNA turnover was also highly conserved in other higher organisms. To test this idea, we characterized RNase T2 proteins from several animal systems. We found evidence supporting the idea that these enzymes also carry out housekeeping functions necessary for cellular homeostasis in animals, and in collaboration with the group of A. Hurlstone (U. of Manchester, UK) we demonstrated that rRNA decay occurs in the zebrafish lysosome, and that RNASET2 is the main activity involved in this turnover. Moreover, deficiencies in this enzyme lead to lysosomal disorders that impact specifically the brain, and in humans are associated with a congenital cystic neuroencephalopathy.

Evolution and functional diversification of the RNase T2 family in plants

Unlike most animals, plants have multiple copies of RNase T2 genes in their genomes. Our analyses showed that this family has undergone a significant adaptive radiation, with evidences of positive selection and gene sorting, indicative of neofunctionalization. To gain a better understanding of these phenomena, we characterized several plant RNase T2 proteins that are not involved in vacuolar degradation of rRNA, from rice, petunia, tobacco, and Arabidopsis. We found that these proteins have gained a diversity of functions, from defensive antimicrobial roles to components of a phosphate scavenging system that is triggered when plants grow under P starvation.

Localization of NnSR1-Cer in endoplasmic reticulum of Arabidopsis leaf protoplasts

Figure from Rojas et al (2015) Plant Science, 236, 250-259

Host plant resistance and management of soybean aphid

In addition to our contribution to the understanding of the molecular events that mediate compatible plant-aphid interactions, we have also investigated the use of host plant resistance genes as a method of aphid control. We have determined molecular mechanisms associated with resistance, and we investigated the effect of combining different resistance genes in one plant at the molecular level, a novel line of research that identified unexpected synergistic effects of this gene pyramiding approach. These synergistic effects could be highly relevant on management strategies, as aphids are fast-evolving insects that can overcome resistance in a short period of time. We also identified new sources of resistance through the screening of soybean germplasm and identified candidate genes underlying these resistance traits.

Mechanisms of ribosomal RNA turnover in plants

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.

Molecular mechanisms mediating plant-aphid interactions

Aphids are one of the main pests of many crops worldwide. These specialized insects cause important economic loses and their management has negative effects on the environment. In Iowa, one of the main pests of soybean is the soybean aphid, which was accidentally introduced in the US in the year 2000. While some important work had been done regarding the biology and ecology of the insect, the soybean-insect interaction had not been analyzed at the molecular level before we started with this project.