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

Abstract

Seed dormancy controls the start of a plant's life cycle by preventing germination of a viable seed in an unfavorable season. Freshly harvested seeds usually show a high level of dormancy, which is gradually released during dry storage (afterripening). Abscisic acid (ABA) has been identified as an essential factor for the induction of dormancy, whereas gibberellins (GAs) are required for germination. The molecular mechanisms controlling seed dormancy are not well understood. DELAY OF GERMINATION1 (DOG1) was recently identified as a major regulator of dormancy in Arabidopsis thaliana. Here, we show that the DOG1 protein accumulates during seed maturation and remains stable throughout seed storage and imbibition. The levels of DOG1 protein in freshly harvested seeds highly correlate with dormancy. The DOG1 protein becomes modified during after-ripening, and its levels in stored seeds do not correlate with germination potential. Although ABA levels in dog1 mutants are reduced and GA levels enhanced, we show that DOG1 does not regulate dormancy primarily via changes in hormone levels. We propose that DOG1 protein abundance in freshly harvested seeds acts as a timer for seed dormancy release, which functions largely independent from ABA.

Spatiotemporal Seed Development Analysis Provides Insight into Primary Dormancy Induction and Evolution of theLepidium DELAY OF GERMINATION1Genes

“…Further support for our conclusion that the L. papillosum 34-kD antigens in Figures 6 and 7 are indeed the LepaDOG1 proteins comes from an interesting observation of Nakabayashi et al (2012). Those authors demonstrated that the AtDOG1 proteins with a calculated molecular mass of approximately 32 kD exhibit significantly slower SDS-PAGE migration (i.e.…”

“…5). Furthermore, we detected transcripts of LepaDOG1a and LepaDOG1c in L. papillosum seeds, a transcript origin also evident for the putative Brassicaceae orthologs LesaDOG1, BrDOG1, and AtDOG1 in L. sativum, B. rapa, and Arabidopsis, respectively (Bentsink et al, 2006;Graeber et al, 2010;Footitt et al, 2011;Nakabayashi et al, 2012). The genomic sequences of LepaDOG1a and LesaDOG1 show more than 80% similarity with highly similar exon regions and, due to conserved splice sites, more than 98% putative amino acid sequence similarity despite rather diverging intron sequences.…”

“…However, as a major advance, we now know from ecological work with Arabidopsis (Huang et al, 2010;Moyers and Kane, 2010;Chiang et al, 2011;Barua et al, 2012;Kronholm et al, 2012) that natural genetic variation at the DOG1 locus is a major determinant for the local adaptation to novel environments, and we also know that the maternal environment controls DOG1 gene expression during seed maturation. For example, low temperature during seed maturation causes increased DOG1 gene expression and deeper primary dormancy of mature seeds (Chiang et al, 2011;Kendall et al, 2011;Nakabayashi et al, 2012). Arabidopsis, therefore, is a very good model also for addressing intraspecific questions in ecological, evolutionary, and developmental biology.…”

“…Discrepancies between calculated and apparent molecular mass seem to be a general phenomenon, as shown by a global proteome analysis of the gel mobility of proteins indicating that more than 40% of the proteins did not migrate within 10% of the predicted position (Shirai et al, 2008). It is interesting that the DOG1 proteins of all three species share a common acidity feature, since Nakabayashi et al (2012) suggested that alteration of the AtDOG1 protein pI value may lead to altered DOG1 function. Figure 7 (left panels) shows that the 34-kD LepaDOG1 proteins are abundant in seeds from type I (young) infructescence FO1 to FO6; all these FOs contain seeds prior to dormancy induction.…”

“…Recent work shows that the AtDOG1 protein accumulates during seed maturation and, unlike the transcript, remains stable throughout imbibition of Arabidopsis seeds . The mother plant environment, especially the ambient temperature during seed development, controls AtDOG1 gene expression during seed maturation as well as the seed dormancy status (Kendall et al, 2011;Nakabayashi et al, 2012).…”