Inheritance of DNA Methylation Patterns and Its Role in Modulating Allelic Expression in Camellia F₁ Hybrids

Area of Science:

• Plant genetics and epigenetics
• Molecular biology
• Genomics

Background:

• DNA methylation, particularly allele-specific methylation (ASM), regulates gene expression and influences hybrid phenotypes.
• ASM's role in allelic expression imbalance (AEI) and its prevalence in hybrids are not well understood due to sequence-dependent mechanisms.

Purpose of the Study:

• To investigate the inheritance of DNA methylation patterns and their impact on allelic expression in F1 hybrids of *Camellia* species.
• To characterize the prevalence and function of ASM in regulating gene expression in hybrid plants.

Main Methods:

• Whole-genome bisulfite sequencing (WGBS)
• Resequencing
• Transcriptome sequencing
• Analysis of DNA methylation patterns and allelic expression in *Camellia* parents and their F1 hybrids.

Main Results:

• F1 hybrids exhibited intermediate DNA methylation levels compared to parents, with partial transmission of parental methylation states.
• Allele-specific methylation (ASM) was infrequent in F1 hybrids, largely due to widespread, randomly distributed biparental parent-specific methylation sites (PSMSs).
• Randomly distributed PSMSs primarily balanced allelic expression, preventing widespread allelic expression imbalance (AEI), although some ASM instances affected flower development genes.

Conclusions:

• ASM is rare in *Camellia* F1 hybrids, with PSMSs playing a key role in balancing allelic expression rather than causing AEI.
• While not always leading to biased expression, ASM can have significant implications for AEI and transgressive phenotypes in hybrids.
• These findings highlight the interplay between genetic and epigenetic factors in regulating gene expression during hybridization, advancing molecular understanding of hybrid vigor.