Regulation of Seed Germination by MFT, MEE26, and CYP89A2 in Arabidopsis thaliana

Germination is the process by which quiescent seeds transition to seedlings. To optimize germination over time, seeds enter a dormant state, which is the inability of a complete viable seed to go through germination even in optimal conditions. In many plant species, seed dormancy can be broken by prolonged storage (after-ripening) or imbibition at low temperatures (stratification). Germination can be affected by several factors such as light. Plants perceive light through a group of photoreceptors that detect Red (R) and Far-red (FR) light. R light such as sunlight promotes germination, however, FR light (shade light found under the canopy) inhibits germination. Light also affects the signalling of phytohormones such as Abscisic Acid (ABA) and Gibberellic Acid (GA). A high ABA/GA ratio is known to be involved in inducing and maintaining seed dormancy. The gene MOTHER-OF-FT-AND-TFL1 (MFT) also affects germination. MFT has been previously shown to promote primary dormancy in Arabidopsis. In this thesis, the function of MFT in after-ripened seeds was investigated and the results indicate that it also promotes dormancy in after-ripened Arabidopsis seeds treated with FR light. This is consistent with the fact that MFT expression has been previously shown to be promoted by FR light. The role of two other genes in the regulation of seed dormancy and germination in both freshly harvested and after-ripened seeds was investigated. They are Cytochrome P450 89A2 (CYP89A2) and Maternal Effect Embryo Arrest 26 (MEE26), which are both regulated by MFT. Expression of CYP89A2 was up-regulated by FR light. Though it is promoted by MFT, phenotypic analysis revealed that freshly harvested seeds of CYP89A2-overexpressor (oe) lines promote germination. This is also the case for after-ripened seeds of CYP89A2oe lines treated with FR light. MEE26 is also promoted by FR light. MEE26oe and silenced lines indicate that it promotes dormancy in freshly harvested seeds and represses germination in after-ripened seeds treated with FR, even though MEE26 is strongly repressed by MFT. This work therefore provides new insight into the function of these genes and shows that the regulation of germination is a complex interaction of different factors.