Takahiro Kawanabe, Sonoko Ishikura, Naomi Miyaji, Taku Sasaki, Li Min Wu, Etsuko Itabashi, Satoko Takada, Motoki Shimizu, Takeshi Takasaki-Yasuda, Kenji Osabe, W. James Peacock, Elizabeth S. Dennis, and Ryo Fujimoto

PLANT BIOLOGY

Significance

Hybrid vigor is an important phenomenon in basic genetics and in agricultural practice, but the bases of the superior performance of the hybrid relative to its parents in biomass and seed production remain elusive. In recent years, it has been suggested that epigenetic controls on levels of gene action are involved. Using mutants of genes involved in DNA methylation, we show that RNA polymerase IV or methyltransferase I do not contribute to the generation of the heterotic phenotype but that decrease in DNA methylation 1, a nucleosome remodeller with an effect on DNA methylation level, is required to produce a full level of hybrid vigor.

Abstract

Hybrid vigor or heterosis refers to the superior performance of F₁ hybrid plants over their parents. Heterosis is particularly important in the production systems of major crops. Recent studies have suggested that epigenetic regulation such as DNA methylation is involved in heterosis, but the molecular mechanism of heterosis is still unclear. To address the epigenetic contribution to heterosis in Arabidopsis thaliana, we used mutant genes that have roles in DNA methylation. Hybrids between C24 and Columbia-0 (Col) without RNA polymerase IV (Pol IV) or methyltransferase I (MET1) function did not reduce the level of biomass heterosis (as evaluated by rosette diameter). Hybrids with a mutation in decrease in dna methylation 1 (ddm1) showed a decreased heterosis level. Vegetative heterosis in the ddm1 mutant hybrid was reduced but not eliminated; a complete reduction could result if there was a change in methylation at all loci critical for generating the level of heterosis, whereas if only a proportion of the loci have methylation changes there may only be a partial reduction in heterosis.

See: http://www.pnas.org/content/113/43/E6704.abstract.html?etoc

PNAS October 25 2016; vol.113; no.43: E6704–E6711

Fig. 3.

Normal levels of heterosis were observed in pol IV mutant hybrids. (A) Ratio of rosette diameter of pol IV mutant hybrids compared with that of Col at 10 DAS. Data represent mean values ± SE obtained from more than 20 plants. (B) Northern blot analysis in pol IV mutant hybrids. Reduction of 24nt-siRNA expression (siR02 and 1003) in the nrpd1a-3 (nrpd1) and sde4-2 x nrpd1a-3 (F₁) was confirmed, but accumulation of 21nt-miRNA (miR171) was not changed. (C) DNA methylation status examined by chop-PCR in the pol IV mutant. No PCR amplification in nrpd1a-3 and sde4-2 x nrpd1a-3 indicated decreased DNA methylation in the endogenous RdDM target AtSN1 (a SINE-like retroelement). The actin gene that does not contain a Hae III site was used as nonmethylated control. (D) RT-PCR analysis of AtSN1 and Solo LTR in leaves. For each locus, −RT shows control lacking reverse transcriptase. GAP (glyceraldehyde-3-phosphate dehydrogenase C subunit) was used as a control.