An investigation into the role of Arabidopsis thaliana NAD metabolising enzymes in plant cellular stress responses

Abstract

Adverse growing conditions resulting from abiotic stresses e.g. pathogen attack results in large losses in crop yields. Understanding and improving plants tolerance to an unfavourable environment remains one of the objectives in the study of plant biotechnology. One growing theory for reducing plant susceptibility to a broad range of stresses is modulation of cellular energy homeostasis. NAD+ (along with ATP) is the most important of cellular energy transducers in the form of a hydrogen ion donor and acceptor. However, a bigger picture is emerging as its role broadens to include a coenzyme, precursor for secondary messengers and a substrate for protein modifications. Three groups of proteins use NAD+ as a substrate, the NAD+ protein deacetylases, poly ADP polymerases and ADP ribose cyclases. Work on these groups of proteins in model organisms have identified their involvement in many biological roles including DNA repair, increasing longevity, initiating apoptosis and regulation of transcription. However, their role in plants is largely unknown. The aim of this study has been to identify the genes involved which use NAD+ and to further characterise their role in plant stress responses. A summary of the main results follows, a) AtPARG2 and sirtuin At5g55760 null lines were more sensitive to DNA damaging agents. b) AtPARG2 lines showed a disruption in circadian rhythm resulting in early flowering. c) Sirtuin At5g09230 null lines were more sensitive to UV-B exposure d) AtPARP3 was highly upregulated with exogenous Abscisic acid application