DNA repair

DNA damage is one of the most harmful stress inducers in living organisms. Studies have shown that exposure to high doses of various types of radiation cause DNA sequence changes (mutation) and disturb protein synthesis, hormone balance, leaf gas exchange and enzyme activity. Recent discovery of a protein called Damage Suppressor Protein (Dsup), found in the tardigrade species Ramazzotius varieornatus, has shown to reduce the effects of radiation damage in human cell lines. We have generated multiple lines of tobacco plants expressing the Dsup gene and preformed numerous tests to show viability and response of these transgenic plants when exposed to mutagenic chemicals, UV radiation and ionizing radiation. We have also investigated Dsup function in association to DNA damage and repair in plants by analyzing the expression of related genes using RT-qPCR. We have also analyzed DNA damage from X-ray and UV treatments using an Alkaline Comet Assay. This project has the potential to help generate plants that are tolerant to more extreme stress environments, particularly DNA damage and mutation, unshielded by our atmosphere. The possibility of growing plants accompanying human space travel and extraterrestrial colonization inspires our imagination. Extremotolerant tardigrade genes such as Dsup may be a valuable avenue in helping to cultivate crops in these future endeavors.

Three important exoribonucleases degrading RNAs in sequence-independent
manner, RNase II, RNase Rand polynucleotide phosphorylase (PNPase), were shown to
protect cells against oxidative stress. This is presumably due to the function of the
exoribonucleases in the removal of oxidized RNA in cells. MutT pyrophosphohydrolase
.was previously reported to scavenge oxidized nucleotides 8-oxoGTP and 8-oxoGDP,
prevent their incorporation into RNA. Deficiency of MutT may lead to an increase in the
level of 8-oxoG in RNA, which may enhance the requirement of the RNA surveillance
function of the exoribonucleases. This study focuses on the roles of the RNA-degradation
exoribonucleases in the removal of oxidatively-damaged RNA in the mutT background.
This work shows that mutT mutation enhances the sensitivity of the RNase mutants to
hydrogen peroxide. Growth defect of the pnp mutT mutant was detected even under
normal aeration, but was rescued to the level of pnp mutant under anaerobic conditions. The pnp mutT mutant shows high mutator activity observed from LacZ reporter system
and high level of 8-oxoG in RNA, strongly suggest that PNPase is responsible for
removing 8-oxoG containing RNAs elevated in mutT background. Additionally, genetic
instability observed from the mutant lacking RNase II and MutT supports the idea that
RNase II may adopt a distinct pathway to reduce deleterious effect from oxidation
challenge.