Plant Epigenetics by Nikolaus Rajewsky Stefan Jurga & Jan Barciszewski

Author:Nikolaus Rajewsky, Stefan Jurga & Jan Barciszewski
Language: eng
Format: epub
Publisher: Springer International Publishing, Cham

5 Proposed Function and Evidences for the Influence of the Epigenetic State in Heterosis

Heterosis refers to the increased vigour of crosses between species (or between distantly related variants within a species) compared with the parents. Although heterosis, or hybrid vigour, has been recognized for well over a century, its molecular basis has remained a matter of debate and is surprisingly poorly understood (reviewed in Birchler et al. 2010; Chen 2010). Recent progress has pointed to a role for epigenetics in heterosis (Groszmann et al. 2011; Greaves et al. 2015). One study showed that altering the transcription of a few regulatory genes through epigenetic variations is associated with growth vigour in hybrids (Ni et al. 2009). Interestingly, Shen et al. (2012), crossing Arabidopsis thaliana C24 and Landsberg erecta ecotypes, obtained F1 hybrids with increased growth and more siliques and also a higher DNA methylation level than either parent. In addition, the growth of both hybrids was more sensitive to a chemical inhibitor of methylation than was that of the parents, supporting a role for DNA methylation in growth vigour. Shen et al. (2012) used high-throughput sequencing to examine the global sRNA expression profiles of the parents and the hybrids. They found that regions of the genome that give rise to sRNAs had increased DNA methylation in all lines, and the hybrids had even higher levels of methylation in those regions. Overall, their data support a model in which regions that give rise to sRNAs and show differential methylation between the parents account for the increased methylation in the hybrids. Shen et al. (2012) also examined the transcriptomes of the parents and hybrids, finding more genes downregulated in the hybrids than upregulated. Integration of the DNA methylome, the sRNAome, and the transcriptome data supports the idea that increased methylation of the circadian clock genes CIRCADIAN CLOCK ASSOCIATED1 and LATE ELONGATED HYPOCOTYL, which have been reported to be involved in heterosis, leads to their downregulated expression in the hybrids. Important results were obtained also recently in Arabidopsis by Kawanabe et al. (2016) who used mutant genes having roles in DNA methylation in order to discover a possible role for epigenetics in the heterosis process. More in particular, they found that hybrids between C24 and Columbia-0 without RNA polymerase IV or methyltransferase I function did not reduce the level of biomass heterosis, whereas hybrids with a mutation in ddm1 showed a decreased heterosis level.

Taken all together, the results, obtained until now, lead to think that exploring the inherited natural variation of epigenetic patterns between genetically diverse strains at a genome-wide level will allow to assess their importance in phenotypic plasticity and might have major consequences for biological research and agriculture (Richards 2008).

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