Tissue-Specific Regulation of Gibberellin Biosynthesis in Developing Pea Seeds

Abstract

Abstract Previous work suggests that gibberellins (GAs) play an important role in early seed development. To more fully understand the roles of GAs throughout seed development, tissue-specific transcription profiles of GA metabolism genes and quantitative profiles of key GAs were determined in pea (Pisum sativum) seeds during the seed-filling development period (8–20 d after anthesis [DAA]). These profiles were correlated with seed photoassimilate acquisition and storage as well as morphological development. Seed coat growth (8–12 DAA) and the subsequent dramatic expansion of branched parenchyma cells were correlated with both transcript abundance of GA biosynthesis genes and the concentration of the growth effector GA, GA1. These results suggest GA1 involvement in determining the rate of seed coat growth and sink strength. The endosperm’s PsGA20ox transcript abundance and the concentration of GA20 increased markedly as the endosperm reached its maximum volume (12 DAA), thus providing ample GA20 substrate for the GA 3-oxidases present in both the embryo and seed coat. Furthermore, PsGA3ox transcript profiles and trends in GA1 levels in embryos at 10 to 16 DAA and also in embryo axes at 18 DAA suggest localized GA1-induced growth in these tissues. A shift from synthesis of GA1 to that of GA8 occurred after 18 DAA in the embryo axis, suggesting that deactivation of GA1 to GA8 is a likely mechanism to limit embryo axis growth and allow embryo maturation to proceed. We hypothesize that GA biosynthesis and catabolism are tightly regulated to bring about the unique developmental events that occur during seed growth, development, and maturation.