Induction of 9- cis -epoxycarotenoid dioxygenase in Arabidopsis thaliana seeds enhances seed dormancy

Abstract

Full understanding of mechanisms that control seed dormancy and germination remains elusive. Whereas it has been proposed that translational control plays a predominant role in germination, other studies suggest the importance of specific gene expression patterns in imbibed seeds. Transgenic plants were developed to permit conditional expression of a gene encoding 9-cis-epoxycarotenoid dioxygenase 6 (NCED6), a rate-limiting enzyme in abscisic acid (ABA) biosynthesis, using the ecdysone receptor-based plant gene switch system and the ligand methoxyfenozide. Induction of NCED6 during imbibition increased ABA levels more than 20-fold and was sufficient to prevent seed germination. Germination suppression was prevented by fluridone, an inhibitor of ABA biosynthesis. In another study, induction of the NCED6 gene in transgenic seeds of nondormant mutants tt3 and tt4 reestablished seed dormancy. Furthermore, inducing expression of NCED6 during seed development suppressed vivipary, precocious germination of developing seeds. These results indicate that expression of a hormone metabolism gene in seeds can be a sole determinant of dormancy. This study opens the possibility of developing a robust technology to suppress or promote seed germination through engineering pathways of hormone metabolism.embryo | endosperm | preharvest sprouting | testa S eed germination is completed by the emergence of the embryo from the seed coat (1), and plants have evolved a number of strategies to regulate germination. Seeds of many species go through dormancy, a period during which germination is suppressed under conditions that are normally favorable for germination (2). Dormancy allows seeds to germinate in appropriate seasons or at locations suitable for seedling growth and further development.

The Putative E3 Ubiquitin Ligase ECERIFERUM9 Regulates Abscisic Acid Biosynthesis and Response during Seed Germination and Postgermination Growth in Arabidopsis

“…10; Supplemental Table S2). Previous studies indicated that NCED6 is highly expressed in the testa and endosperm, and its overexpression results in increased ABA levels in seeds and enhanced seed dormancy (Lefebvre et al, 2006;Martínez-Andújar et al, 2011). The up-regulation of NCED6 expression in cer9 mutant seeds thus may contribute to the higher ABA level and increased seed dormancy of the mutants.…”

Expression of9-cis-EPOXYCAROTENOID DIOXYGENASE4Is Essential for Thermoinhibition of Lettuce Seed Germination but Not for Seed Development or Stress Tolerance

“…Specific induction of NCED6 during Arabidopsis seed development is sufficient to enhance seed dormancy (Martínez-Andújar et al, 2011). In mature lettuce seeds, NCED4 mRNA is present in the embryo, but not in the endosperm ; information on NCED4 expression during lettuce seed development has not been reported.…”

“…NCED3 together with NCED5 are important regulators of ABA levels during water stress in Arabidopsis, and their transcripts are induced by drought (Tan et al, 2003;Ruggiero et al, 2004;Frey et al, 2012). Arabidopsis NCED5, NCED6, and NCED9 play important roles in ABA synthesis in the embryo and endosperm during dormancy induction (Lefebvre et al, 2006;Seo et al, 2006;Martínez-Andújar et al, 2011;Frey et al, 2012). NCED6 is regulated by light and its mutation promoted seed germination in the dark, whereas NCED9 and NCED5 are induced by high temperature in the imbibed seeds and their mutation resulted in loss of thermoinhibition Toh et al, 2008).…”

ArabidopsisPaired Amphipathic Helix Proteins SNL1 and SNL2 Redundantly Regulate Primary Seed Dormancy via Abscisic Acid–Ethylene Antagonism Mediated by Histone Deacetylation

“…Altered expression of genes regulating ABA levels or sensitivity leads to changed seed dormancy levels (Rodríguez-Gacio et al, 2009). Induction of NCED6 during imbibition increases ABA levels and is sufficient to prevent seed germination (Martínez-Andújar et al, 2011). The ABA 89-hydroxylase mutants cyp707a2 and cyp707a1 and the double mutant cyp707a2 cyp707a1 accumulate ABA in dry and imbibed seeds and exhibit enhanced seed dormancy (Saito et al, 2004;Okamoto et al, 2006).…”