Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/24/2017
Publication Date: 6/19/2017
Citation: Nelson, S.K., Steber, C.M. 2017. Transcriptional mechanisms associated with seed dormancy and dormancy loss in the gibberellin-insensitive sly1-2 mutant of Arabidopsis thaliana. PLoS One. 12:(6)e0179143.
Interpretive Summary: Too little seed dormancy causes susceptibility to preharvest sprouting in cereal crops, whereas too much seed dormancy can lead to problems with poor emergence in crop plants. This study investigates the seed dormancy mechanisms controlled by the plant hormone gibberellin A (GA) and by the DELLA family of repressors of seed germination. GA and the positive regulator of GA signaling called SLY1 appear to be major regulators of genes involved in protein translation. Rescue of germination by a period of dry storage called after-ripening was associated with many changes in gene expression, whereas stimulation of germination by the GA hormone receptor GID1b resulted in few changes in gene expression. This makes us wonder if GA signaling may also be regulating nontranscriptional mechanisms of dormancy control.
Technical Abstract: While widespread transcriptome changes have been previously observed with seed dormancy loss, this study specifically characterized transcriptional changes associated with the increased seed dormancy and dormancy loss of the gibberellin (GA) hormone-insensitive sleepy1-2 (sly1-2) mutant. The SLY1 gene encodes the F-box subunit of an SCF E3 ubiquitin ligase needed for GA-triggered proteolysis of DELLA repressors of seed germination. DELLA overaccumulation in sly1-2 seeds leads to increased dormancy that can be rescued without DELLA protein destruction either by extended dry after-ripening (11 months, 51% germination) or by overexpression of the GA receptor, GA-INSENSITIVE DWARF1b (GID1b-OE) (74% germination). Approximately half of the transcriptome changes due to after-ripening appear to depend on DELLA proteolysis. After-ripening resulted in different transcriptional changes in early versus late Phase II of imbibition that were consistent with the processes known to occur. Dormancy loss through after-ripening led to a SLY1- and GA-dependent increase in transcripts involved in protein translation, suggesting that increasing germination capacity involves activation of translation. While sly1-2 after-ripening was associated with transcript-level changes in 4594 genes over two imbibition timepoints, rescue of sly1-2 germination by GID1b-OE was associated with changes in only 23 genes. Thus, a big change in sly1-2 germination phenotype can occur with relatively little change in the global pattern of gene expression. Most GID1b-OE-responsive transcripts showed similar changes with after-ripening in early Phase II of imbibition, but opposite changes with after-ripening by late Phase II. This suggests that GID1b-OE stimulates germination early in imbibition, but may later trigger negative feedback regulation.