Leaf senescence is driven by the expression of senescence-associated genes (SAGs). Developmentspecific genes often undergo DNA demethylation in their promoter and other regions, which regulates gene expression. Whether and how DNA demethylation regulates the expression of SAGs and thus leaf senescence remain elusive. Whole-genome bisulfite sequencing (WGBS) analyses of wild-type (WT) and demeter-like 3 (dml3) Arabidopsis leaves at three developmental stages revealed hypermethylation during leaf senescence in dml3 compared with WT, and 20 556 differentially methylated regions (DMRs) were identified by comparing the methylomes of dml3 and WT in the CG, CHG, and CHH contexts. Furthermore, we identified that 335 DMR-associated genes (DMGs), such as NAC016 and SEN1, are upregulated during leaf senescence, and found an inverse correlation between the DNA methylation levels (especially in the promoter regions) and the transcript abundances of the related SAGs in WT. In contrast, in dml3 the promoters of SAGs were hypermethylated and their transcript levels were remarkably reduced, and leaf senescence was significantly delayed. Collectively, our study unraveled a novel epigenetic regulatory mechanism underlying leaf senescence in which DML3 is expressed at the onset of and during senescence to demethylate promoter, gene body or 3 0 UTR regions to activate a set of SAGs.
Chimeras have been used to study the transmission of genetic material and the resulting genetic variation. In this study, two chimeras, TCC and TTC (where the origin of the outer, middle, and inner cell layers, respectively, of the shoot apical meristem is designated by a ‘T’ for tuber mustard and ‘C’ for red cabbage), as well as their asexual and sexual progeny, were used to analyse the mechanism and the inheritance of the variation induced by grafting. Asexual TCC progeny were obtained by adventitious shoot regeneration, while TTC sexual progeny were produced by self-crossing. This study observed similar morphological variations in both the asexual and sexual progeny, including changes in leaf shape and the pattern of shoot apical meristem termination. The leaf shape variation was stable, while the rate of shoot apical meristem termination in the TTC progenies decreased from 74.52% to 3.01% after three successive rounds of self-crossing. Specific red cabbage small RNAs were found in the asexually regenerated plants (rTTT) that were not present in TTT, indicating that small RNAs might be transmitted from red cabbage to tuber mustard during grafting. Moreover, in parallel with the variations in phenotype observed in the progeny, some conserved miRNAs were differentially expressed in rTTT and TTT, which correlated with changes in expression of their target genes. These results suggest that the change in small RNA expression induced by grafting may be an important factor for introducing graft-induced genetic variations, providing a basis for further investigating the mechanism of graft-induced genetic variation through epigenetics.
The
changes of anisotropic adsorption–swelling and permeability
with injecting CO2 in coal influence the CO2 injectivity during CO2-ECBM or CGS (ECBM = enhancing
coal bed methane; CGS = CO2 geological sequestration).
To strengthen the understanding
of this issue, two special-made cubic coal samples were adopted to
test the porosity, swelling, and permeability in parallel face cleat
and bedding plane direction, parallel butt cleat and bedding plane
direction, and vertical bedding plane direction. To quantitatively
characterize the anisotropic porosity, anisotropic swelling, and anisotropic
permeability, an anisotropy index was introduced in this work. The
results show that porosity anisotropy reflects the pore connectivity
in different directions, which fall in the order of parallel face
cleat and bedding plane direction > parallel butt cleat and bedding
plane direction > vertical bedding plane direction.
The
porosity varieties can be owed to the compaction effect, thermal evolution
effect, banded structure, and cleat distribution in coal seams. The
maximum swelling ratios of the vertical bedding plane direction to
the parallel bedding plane direction are 2.30 in sample 1 and 1.89
in sample 2. However, the ratios of parallel face cleat to parallel
butt cleat are 1.28 in sample 1 and 1.30 in sample 2. The inhomogeneity
of matter composition in the vertical bedding direction and the difference
of cleat distribution in various coal bands mainly cause the anisotropic
swelling. Both injecting CO2 in coal and raising its temperature
increase the anisotropy swelling index, but the effect of thermal
swelling is quite weak. Adsorbing CO2 especially for supercritical
CO2 will enhance the permeability anisotropy of coal. This
is because the low-permeability cleat possesses higher permeability
adsorption sensitivity and the bedding plane fracture with higher
permeability instead does not produce a pronounced permeability drop
because of its lower permeability adsorption sensitivity. Cleats that
are easily affected by adsorption–swelling always serve as
throats between fractures and the coal matrix in a high-anisotropic
coal, which will restrain CO2 flow in coal pores. Accordingly,
cleat seepage and corresponding potential enhanced permeability measures
deserve being paid enough attention to in future research. This work
clarifies the understanding and offers some implications for CO2 injecting into coal seams from the perspective of anistropic
properties of coal.
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