Nucleolar dominance in triticales: control by unlinked genes

Area of Science:

• Plant genetics
• Molecular biology
• Genomics

Background:

• Hybrid organisms often exhibit gene silencing, particularly of ribosomal DNA (rDNA) from one parent.
• In triticale (wheat x rye), rye rDNA on chromosome 1R is usually inactive, while wheat rDNA on chromosomes 1B and 6B is expressed.

Purpose of the Study:

• To investigate the genetic mechanisms controlling ribosomal DNA (rDNA) expression in wheat-rye hybrids.
• To determine if altering chromosome composition can overcome rDNA suppression in triticale.

Main Methods:

• Utilizing silver staining to visualize and quantify active ribosomal DNA (rDNA) sites in interphase and metaphase cells.
• Analyzing triticale lines with specific chromosome substitutions (e.g., triticale-2D(2R)) and wheat-rye chromosomal addition lines.

Main Results:

• Substitution of rye chromosome 2R with wheat chromosome 2D in triticale (triticale-2D(2R)) reactivated the normally suppressed rye-origin rDNA.
• All six major rDNA loci (from both wheat and rye origins) became active in the modified triticale.
• Similar rDNA expression patterns were observed in different triticale lines and wheat-rye addition lines, supporting the findings.

Conclusions:

• Chromosomal interactions play a critical role in regulating ribosomal DNA (rDNA) gene expression in interspecific hybrids.
• Specific chromosome substitutions can overcome parental gene silencing, leading to the activation of previously suppressed rDNA loci.
• The study provides insights into the complex epigenetic and genetic controls governing rDNA activity in polyploid plants.