Abstract
The involvement of chromatin remodelling in dormancy cycling in the soil seed bank (SSB) is poorly understood. Natural variation between the winter and summer annual Arabidopsis ecotypes Cvi and Bur was exploited to investigate the expression of genes involved in chromatin remodelling via histone 2B (H2B) ubiquitination/de-ubiquitination and histone acetylation/deacetylation, the repressive histone methyl transferases CURLY LEAF (CLF) and SWINGER (SWN), and the gene silencing repressor ROS1 (REPRESSOR OF SILENCING1) and promoter of silencing KYP/SUVH4 (KRYPTONITE), during dormancy cycling in the SSB. ROS1 expression was positively correlated with dormancy while the reverse was observed for CLF and KYP/SUVH4. We propose ROS1 dependent repression of silencing and a sequential requirement of CLF and KYP/SUVH4 dependent gene repression and silencing for the maintenance and suppression of dormancy during dormancy cycling. Seasonal expression of H2B modifying genes was correlated negatively with temperature and positively with DOG1 expression, as were histone acetyltransferase genes, with histone deacetylases positively correlated with temperature. Changes in the histone marks H3K4me3 and H3K27me3 were seen on DOG1 (DELAY OF GERMINATION1) in Cvi during dormancy cycling. H3K4me3 activating marks remained stable along DOG1. During relief of dormancy, H3K27me3 repressive marks slowly accumulated and accelerated on exposure to light completing dormancy loss. We propose that these marks on DOG1 serve as a thermal sensing mechanism during dormancy cycling in preparation for light repression of dormancy. Overall, chromatin remodelling plays a vital role in temporal sensing through regulation of gene expression.
Highlights
Seeds in the soil seed bank (SSB) continually adjust their dormancy status to synchronise germination and seedling emergence to an appropriate climate space and time of the year
We previously suggested that DELAY OF GERMINATION1 (DOG1) is part of a thermal sensing mechanism that measures the passage of time with the accumulation of DOG1 protein serving to represent accumulated thermal time to regulate the depth and persistence of dormancy (Footitt et al, 2014)
Dormancy in Cvi rapidly increased on burial in the field in autumn; dormancy was maximal until April after which it declined to a low point during the summer months before increasing again in autumn (Figure 1a)
Summary
Seeds in the soil seed bank (SSB) continually adjust their dormancy status to synchronise germination and seedling emergence to an appropriate climate space and time of the year. This allows multiple species to compete successfully within species rich natural communities (Baskin and Baskin, 2006; Walck et al, 2011). Some signals (e.g., soil temperature and moisture) are related to temporal sensing, the slow seasonal change that indicates when a suitable time of year exists (temporal window) Integrated over time these signals alter the depth of dormancy and the sensitivity to a second set of signals (e.g., light, nitrate, alternating temperatures). The resulting dormancy cycling coupled with seed longevity represents a bet-hedging strategy for the short- and long-term persistence of native/weed species within the
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