|HAUVERMALE, AMBER - Washington State University|
Submitted to: Plant Signaling and Behavior
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/26/2019
Publication Date: 1/21/2020
Citation: Hauvermale, A.L., Steber, C.M. 2020. GA signaling is essential for the embryo-to-seedling transition during Arabidopsis seed germination, a ghost story. Plant Signaling and Behavior. 15(1):1-9. https://doi.org/10.1080/15592324.2019.1705028.
Interpretive Summary: Plant embryos survive for extended periods of time in an arrested state in dry seeds. This is tremendously useful to agriculture because it allows us to store seeds for extended periods of time because using them to propagate crop species. Once a plant embryo placed in what is essentially a state of suspended animation in a dry seed, there must be a mechanism to reactivate growth and development. This study provides evidence that this plant hormone GA can serve as this wake up call. When GA hormone can’t be made or when the genes needed to respond to GA are missing, the seed cannot germinate. Moreover, if that germination is forced either genetically or by physically removing the seed coat, the seedling cannot compete development unless GA hormone is applied, BEFORE the seed germinates. This provides strong evidence for GA as the wake up call for seed germination.
Technical Abstract: The plant hormone gibberellin (GA) plays key roles in developmental transitions including seed germination, flowering, and the transition from juvenile to adult growth stage. This study provides evidence that the GA receptor GID1 (GA-INSENSITIVE DWARF1) also plays an essential role in the embryo-to-seedling transition. The Arabidopsis thaliana ga1-3 GA biosynthesis mutant fails to germinate without GA application. This study discovered that overexpression of the GID1a, GID1b, and GID1c GA receptors rescues the germination of a small percentage of ga1-3 seeds without GA application. This is interesting given that the gid1abc triple mutant cannot germinate unless the seed coat is cut. However, most of these germinating gid1abc seedlings arrested during the embryo-to-seedling transition. GID1-rescue of ga1-3 germination was improved with partial after-ripening and cold stratification. Although ga1-3 GID1-OE seeds were capable of germination, they also arrested in the embryo-to-seedling transition. This growth arrest was rescued by pre-germinative but not by post-germinative GA application. This observation suggests that GA signaling is important for the embryo-to-seedling transition prior to emergence from the seed coat, and may be regulated by the three Arabidopsis GA receptors, GID1a, GID1b, and GID1c.