The DELLA-LDL mediated control of germination via DELAY OF GERMINATION 1.

Abstract

Germination is the process of a seed beginning to grow, and the proper timing of germination is vital to both plants and humans. Further understanding of the control of germination may contribute towards the improvement of human agriculture and the alleviation of major problems, such as pre-harvest sprouting in cereal crops. Seed dormancy ensures that germination occurs in favourable conditions and is regulated by the gibberellins and their repressors, the DELLA proteins. DELAY OF GERMINATION 1 (DOG1) has been labelled the master regulator of germination due to its considerable impact on seed dormancy. There is an emerging role for LYSINE-SPECIFIC DEMETHYLASE LIKE 1 and 2 (LDL1 and LDL2), chromatin remodelling enzymes (CREs) which regulate chromatin dynamics to repress DOG1 expression and seed dormancy.

This thesis explored the possibility of interactions between the DELLAs and CREs through protein-protein interaction assays using a screening library designed to identify molecular interactions between hormone signalling genes and chromatin remodelling enzymes. The meaning of these interactions was explored through numerous experiments in the model plant species Arabidopsis thaliana, including analyses of germination timing combined with analyses of DOG1 expression. These analyses were conducted in multiple conditions, including altering the balance of GAs, and the use of a 5PLE (quintuple DELLA) mutant lacking all five DELLA proteins.

This thesis identifies multiple interactions between the DELLA and LDL proteins, amongst further interactions between the DELLAs and other chromatin remodelling enzymes. The combined germination and expression analyses report that the DELLA proteins are important in regulating DOG1, specifically through their role in cold-stratification mediated abolition of seed dormancy. Through integrating novel results reported with current research, this thesis proposes that the DELLA-LDL interactions are implicit in maintaining dormancy in unstratified seeds via DOG1 and that the cold-stratification which breaks seed dormancy may also break the DELLA-LDL reaction, enabling germination.