Figure 1.
Schematic representation of Arabidopsis Cvi seed treatments and physiological status of the seeds.
(A) The inception of primary seed dormancy occurs during seed maturation. Mature dry seeds are dormant (1) and are maintained in this state when imbibed at 22°C, even for 14 d (2). A sufficiently long period of moist chilling (4°C) will break dormancy (3). Light (sun symbol) can induce germination at 22°C once dormancy is broken by moist chilling – seeds commence germination (4), which proceeds to radicle protrusion, signifying the completion of germination (5). The next transition is from germination to seedling growth/development (6). (B) Characterization of seed dormancy of Arabidopsis ecotype Cvi. Moist chilling is required for 14 d to subsequently elicit the full germination potential of seeds. Data are based on mean values of three replicates of 50 seeds +/− SE.
Figure 2.
Expression analyses of histone methyltransferases (HMTs) in Arabidopsis Cvi seeds.
(A) Class I SET-domain HMTs. (B, C) Class III SET-domain HMTs. Mean of three biological replicates +/− SE are shown. Note that the Y-axis for the RNA data is in log 10-scale.
Figure 3.
Expression analyses and histone H3 methylation pattern changes of germination-associated genes in Arabidopsis Cvi.
nChIP/qPCR (left column) and expression analyses (right column); averages of three biological replicates are shown +/− SE. ER = endosperm rupture (completion of germination). Note that the Y-axis for the RNA data is in log-scale.
Figure 4.
Expression analyses and histone H3 methylation pattern changes of regulators of seed maturation/dormancy in Arabidopsis Cvi.
nChIP/qPCR (left column) and expression analyses (right column); averages of three biological replicates are shown +/− SE. Numbers 1–6 correspond to the stages noted on the X-axis for DOG1. ER = endosperm rupture (completion of germination). Note that the Y-axis for the RNA data is in log-scale.
Figure 5.
Expression analyses and histone H3 methylation pattern changes of CnABI3 in yellow-cedar.
(A) Embryos (B) Megagametophytes. nChIP/qPCR (left column) and expression analyses (right column). Averages of three biological replicates are shown +/− SE. Mature yellow-cedar seeds were subjected to a full (12-week) dormancy-breaking treatment, or the full dormancy-breaking treatment followed by 1 day in germination conditions (“germinating”). Seedlings were at an early stage (4 mm radicle length, and greened cotyledons). A control treatment consisted of maintaining seeds in warm, moist conditions for 12 weeks, which did not break dormancy.
Figure 6.
Model illustrating the essential role of histone modifications during seed-to-seedling and vegetative-to-generative phase transitions.
Repressive H3K27me3 marks on genes encoding key regulators of dormancy, such as ABI3, are deposited through the PRC2 complex, and replace the activating H3K4me3 mark in response to the environmental cue of moist chilling, similar to the vernalization response on the FLC locus. In order to fulfill its role as a flowering repressor, the FLC locus has to be re-activated after seed germination. ATXR7 might be involved in this process [46].