A seed coat bedding assay shows that RGL2-dependent release of abscisic acid by the endosperm controls embryo growth in Arabidopsis dormant seeds

Abstract

Seed dormancy is an ecologically important adaptive trait in plants whereby germination is repressed even under favorable germination conditions such as imbibition with water. In Arabidopsis and most plant species, dormancy absolutely requires an unidentified seed coat germination-repressive activity and constitutively higher abscisic acid (ABA) levels upon seed imbibition. The mechanisms underlying these processes and their possible relationship are incompletely understood. We developed a "seed coat bedding" assay monitoring the growth of dissected embryos cultured on a layer of seed coats, allowing combinatorial experiments using dormant, nondormant, and various genetically modified seed coat and embryonic materials. This assay, combined with direct ABA measurements, revealed that, upon imbibition, dormant coats, unlike nondormant coats, actively produce and release ABA to repress embryo germination, whatever the embryo origin, i.e., from dormant, nondormant, or never dormant aba seeds, unable to synthesize ABA. The persistent high ABA levels in imbibed dormant seeds requires the permanent expression of the DELLA gene RGL2, where it remains insensitive to gibberellins (GA) unlike in nondormant seeds. These findings present the seed coat as an organ actively controlling germination upon seed imbibition and provide a framework to investigate how environmental factors break seed dormancy.gibberellins | seed dormancy | DELLA | seed germination | ABI5

Temperature variability is integrated by a spatially embedded decision-making center to break dormancy in Arabidopsis seeds

“…1 and Supplementary Table 1). It has been established that germination is ultimately initiated within the Arabidopsis embryo and that this process is informed by the endosperm (10,12,21,22). The cellular locations underlying this decision-making process remain unknown, however.…”

AtGASA6 Serves as an Integrator of Gibberellin-, Abscisic Acid- and Glucose-Signaling during Seed Germination in Arabidopsis

“…AtGASA6 Is Located Downstream of RGL2 to Integrate Glc and GA Signaling Because RGL2 plays an essential role in integrating GA and ABA signaling during seed germination (Piskurewicz et al, 2008;Lee et al, 2010) and because our results suggest that AtGASA6 plays an integral role in Glc, ABA, and GA signaling pathways and functions downstream of RGL2 in GA pathway, we hypothesized that the response of AtGASA6 to Glc and GA is also regulated by RGL2. To verify this, mutant seeds of rgl2-13, rgl2-13/gasa6-1, and gasa6-1 were , and GIN2 in the GA, ABA, and Glc signaling pathways.…”

“…The roles of ABA in modulating seed development, dormancy, germination, and plant adaptation to abiotic environmental stresses, have been well studied (Gubler et al, 2005;Finkelstein et al, 2008), and it has been found that ABA specifically inhibits endosperm rupture rather than testa rupture in the seed germination process (Müller et al, 2006;Lee et al, 2010). ABA signaling components include ABSCISIC ACID-INSENSITIVE3 (ABI3), which encodes a B3 domain transcription factor, and ABI5, encoding a basic Leu zipper transcription factor, both of which are necessary for growth arrest when germinating seeds encounter unfavorable conditions (Giraudat et al, 1992;Finkelstein and Lynch, 2000).…”

The Time Required for Dormancy Release in Arabidopsis Is Determined by DELAY OF GERMINATION1 Protein Levels in Freshly Harvested Seeds

“…Both dormant and nondormant seeds show a decline in their ABA levels within the first 12 h of imbibition. Thereafter, dormant seeds show consistently higher ABA levels than nondormant seeds (Ali-Rachedi et al, 2004;Lee et al, 2010). We studied the expression kinetics of ABA and GA metabolic genes during imbibition of fresh mature Ler, dog1-1, and NIL DOG1 seeds in detail.…”