Seed after‐ripening is a discrete developmental pathway associated with specific gene networks in Arabidopsis

Abstract

SummaryAfter-ripening (AR) is a time and environment regulated process occurring in the dry seed, which determines the germination potential of seeds. Both metabolism and perception of the phytohormone abscisic acid (ABA) are important in the initiation and maintenance of dormancy. However, molecular mechanisms that regulate the capacity for dormancy or germination through AR are unknown. To understand the relationship between ABA and AR, we analysed genome expression in Arabidopsis thaliana mutants defective in seed ABA synthesis (aba1-1) or perception (abi1-1). Even though imbibed mutant seeds showed no dormancy, they exhibited changes in global gene expression resulting from dry AR that were comparable with changes occurring in wildtype (WT) seeds. Core gene sets were identified that were positively or negatively regulated by dry seed storage. Each set included a gene encoding repression or activation of ABA function (LPP2 and ABA1, respectively), thereby suggesting a mechanism through which dry AR may modulate subsequent germination potential in WT seeds. Application of exogenous ABA to after-ripened WT seeds did not reimpose characteristics of freshly harvested seeds on imbibed seed gene expression patterns. It was shown that secondary dormancy states reinstate AR status-specific gene expression patterns. A model is presented that separates the action of ABA in seed dormancy from AR and dry storage regulated gene expression. These results have major implications for the study of genetic mechanisms altered in seeds as a result of crop domestication into agriculture, and for seed behaviour during dormancy cycling in natural ecosystems.

The N-end rule pathway promotes seed germination and establishment through removal of ABA sensitivity in Arabidopsis

“…Mechanisms regulating after-ripening are not well understood (11,13). Previously, it has been shown that catabolism of ABA in imbibed seeds is an important regulator of germination potential, and that seeds lacking ABA 8Ј-hydroxylase activity exhibit enhanced dormancy (14,15).…”

“…Arabidopsis seed germination is regulated by intrinsic hormonal pathways and external environmental signals, which influence whether an imbibed seed completes germination or remains dormant (10)(11)(12). Dry Arabidopsis seeds exhibit physiologically non-deep dormancy, and following shedding they go through a period of after-ripening, through which the capacity for dormancy is lost (10,13). The Arabidopsis embryo is surrounded by 2 structures: a single endosperm cell layer and an external, dead testa layer that is maternally derived (11).…”

A Pivotal Role of the Basic Leucine Zipper Transcription Factor bZIP53 in the Regulation ofArabidopsisSeed Maturation Gene Expression Based on Heterodimerization and Protein Complex Formation

“…In this respect, its participation in a ternary complex with C/S bZIPs might partly explain many of numerous pleotropic effects observed in abi3 mutants. Interestingly, transcriptomic data suggest that bZIP53 and bZIP10 expression levels are reduced in mutant abi3-4 developing seeds (Carrera et al, 2008).…”

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

“…Mature seeds require a period of after-ripening to overcome dormancy (Carrera et al, 2008). Two-weekold freshly harvested cer9-2 seeds exhibited a higher rate (80%) of dormancy than the wild-type Columbia-0 (Col-0; 16%; Fig.…”