Roles and mechanisms of DNA repair factors and pathways in Maintaining Seed Quality.

Successful germination is a major determinant of crop yields and survival of plants in the natural environment. Our knowledge of molecular factors important to seed quality is far from complete, yet such understanding is vital in the endeavour of mitigating the detrimental effects of extended storage on seed vigour and viability. Genome integrity is crucial for cellular survival and transmission of genetic information. A number of pre-genomic era studies identified strong correlations between DNA damage accumulated in the quiescent seed and seed ageing. If unrepaired, DNA damage results in delayed growth, mutagenesis and cell death. Damage products incurred by DNA are remarkably heterologous and plants have evolved multiple pathways to facilitate the repair of specific damage products. Through the isolation and analysis of knockout Arabidopsis mutants, this work identifies and characterises DNA repair genes whose action is required during seed imbibition. These studies examined the importance of four major DNA repair pathways in germination and seed quality. Mutants deficient in non-homologues end joining (KU70 and KU80), homologues recombination (XRCC2) and base excision repair (ARP) DNA repair pathways were all found to be hypersensitive to accelerated ageing treatment but those deficient in nucleotide excision repair (ERCC1) were not. Therefore this work establishes roles for multiple DNA repair pathways in seed longevity. Comparative analysis also defined non-homologues end joining as the most important DNA repair pathway to seed quality. LIG6 encodes a unique plant specific DNA ligase with roles in seed longevity and implicated in repair of DSBs but remains largely uncharacterised to date. Here studies using extra-chromosomal recombination assays demonstrate LIG6 functions in the promotion of recombination activities in Arabidopsis protoplasts. Further studies demonstrate the involvement of LIG6 in the maintenance of root meristem genome stability. Collectively, this work provides an increased understanding of the early events central to the germination process and seed longevity.