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DNA methylation interaction mediated by RdDM is not involved in hybrid vigor


Hybrid vigor, or heterosis,is paramount trait for plant growth and crop breeding. The molecular mechanism is debating and unclear for a long term, although several models were proposed. Arabidopsis, a model plant, is suitable for detection of heterosis mechanism, in which the F1 hybrids by crossing different accessions exhibited clear growth hybrid vigor in the early development stages. Previously, RdDM pathway (RNA directed DNA methylation) is highly suggested to be responsible for the higher DNA methylation levels and 24nt siRNA profiles of F1 hybrids compared to parents, and thereby involved in regulation of hybrid vigor. But it remain concrete evidence.
Prof. Jian-Kang Zhu’s lab at the Shanghai Center for Plant Stress Biology, CAS, developed a new epigenomic algorithm identifying more than 3000 methylation interaction loci including not only hundreds of loci locating in the DMRs (differentially methylated regions) between parents as previously reported, but more than 2000 loci derived from SMRs (similarly methylated regions) newly identified in the study. After NRPD1 and NRPE1, the key factors of RdDM pathway, are mutated, the DNA methylation interaction was lost, clearly indicating that RdDM regulates the DNA methylation interactions in Arabidopsis. Unexpectedly, hybrid vigor was still maintained after dysfunction of NRPD1 and NRPE1. Thus, RdDM is not involved in regulation of hybrid vigor although it is critical for maintenance of DNA methylation interaction in hybridization. It further demonstrated that DNA methylation is not an important epigenetic factor for regulation of hybrid vigor.
This work was published online in PNAS (Zhang et al.) on July 6 2016, entitled as “Methylation interactions in Arabidopsis hybrids require RNA-directed DNA methylation and are influenced by genetic variation”. It was supported by funding from the Chinese Academy of Sciences and by a grant from the NIH (National Institutes of Health), USA.

A. DNA methylation is affected by RdDM pathway;
B. Growth hybrid vigor is not changed by dysfunction of Pol IV and Pol V.
(Image by Dr Qingzhu Zhang)

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