In rice (Oryza sativa L.), seeds exposed to heat
stress during grain filling exhibit delayed germination because of
DNA methylation levels at promoters of abscisic acid (ABA, a germination-inhibiting
hormone) catabolism genes and α-amylase (starch-hydrolyzing
enzyme) genes, affecting their expression levels. Cold atmospheric
plasma is known as an innovative and sustainable energy that has positive
effects on the growth and development of many plant species. We, therefore,
treated seeds that matured under heat stress with cold plasma and
found that subsequent germination was significantly restored; genes
involved in ABA biosynthesis (OsNCED2 and OsNCED5) were downregulated, whereas genes involved in ABA
catabolism (OsABA8′OH1 and OsABA8′OH3) and α-amylase genes (OsAmy1A, OsAmy1C, OsAmy3B, and OsAmy3E) were upregulated.
Cold plasma treatment caused significant hypermethylation of the OsNCED5 promoter and hypomethylation of OsAmy1C and OsAmy3E promoters, which matched their expression
patterns. We suggest that cold plasma treatment can significantly
improve the germination of rice seeds affected by heat stress by affecting
epigenetic regulation.
High temperature during grain filling considerably reduces yield and quality in rice (Oryza sativa L.); however, how high temperature affects seed germination of the next generation is not yet well understood. Here, we report that seeds from plants exposed to high temperature during the grain filling stage germinated significantly later than seeds from unstressed plants. This delay remained even after dormancy release treatments, suggesting that it was not due to primary seed dormancy determined during grain filling. In imbibed embryos of heat-stressed seeds, expression of abscisic acid (ABA) biosynthesis genes (OsNCEDs) was higher than in those of control seeds, whereas that of ABA catabolism genes (OsABA8′OHs) was lower. In the aleurone layer, despite no change in GA signaling as evidenced by no effect of heat stress on OsGAMYB gene expression, the transcripts of α-amylase genes OsAmy1C, OsAmy3B, and OsAmy3E were significantly down-regulated in heat-stressed seeds in comparison with controls. Changes in promoter methylation levels were consistent with transcriptional changes of ABA catabolism-related and α-amylase genes. These data suggest that high temperature during grain filling results in DNA methylation of ABA catabolism-related and α-amylase gene promoters, delaying germination of heat-stressed seeds.
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