Epigenetic inheritance in rice plants.

Area of Science:

• Plant molecular biology
• Epigenetics
• Genomics

Background:

• Epigenetics regulates gene expression without altering DNA sequences, often via DNA cytosine methylation.
• While epigenetic inheritance is suspected, gene-level evidence linking methylation to heritable traits remains limited.
• This study investigates genes whose methylation status directly correlates with inherited phenotypic changes.

Purpose of the Study:

• To identify specific genes in rice whose DNA methylation patterns are directly inherited across generations.
• To determine if changes in DNA methylation can lead to stable, heritable phenotypic alterations, such as disease resistance.
• To provide direct evidence for gene-level epigenetic inheritance.

Main Methods:

• Rice seeds were treated with 5-azadeoxycytidine to reduce DNA methylation in vivo.
• Progeny were cultivated for over 10 years, and genomic regions with altered methylation were screened using methylation-sensitive amplified polymorphism (MSAP).
• Bisulfite mapping confirmed cytosine methylation changes, and pathogen infection assays were conducted using Xanthomonas oryzae.

Main Results:

• A dwarfism phenotype (Line-2) was stably inherited over nine generations following DNA methylation reduction.
• Demethylation of a retrotransposon gag-pol polyprotein gene and the Xa21G gene promoter was observed in Line-2.
• Constitutive expression of Xa21G in Line-2 conferred resistance to Xanthomonas oryzae, while wild-type plants were susceptible.

Conclusions:

• Selective promoter demethylation of Xa21G abolished silencing, leading to acquired disease resistance that was stably inherited.
• This study provides a clear example of epigenetic inheritance at the gene level.
• The findings support the concept of Lamarckian inheritance, where acquired traits can be passed to offspring.