Researchers Reveal New Insights into Nucleolar Dominance of Newly Resynthesized Hexaploid Wheat

Dr. HAN Fangpu's group from the Institute of Genetics and Developmental Biology of the Chinese Academy of Sciences reports the new insights on the evolution of nucleolar dominance in newly resynthesized hexaploid wheat Triticum Zhukovskyi in an article published online in The Plant Journal (https://doi.org/10.1111/tpj.16320).

Nucleolar dominance (ND) is a widespread epigenetic phenomenon in distant hybridizations, which describes reversible nucleolus transcription failure at the uniparental nucleolus organizing region (NOR). However, the dynamics and transcription of NORs in speciation of Triticum zhukovskyi (GGA^uA^uA^mA^m) have not been reported.

In the current study, the researchers discover that T. zhukovskyi lost A^u genome NORs during the first polyploidization, but retained A^m genome NORs across the second polyploidization process. However, the rRNA genes from the A^m genome were silenced in F₁ hybrids (GA^uA^m) and remained inactive after chromosome doubling. Furthermore, in the case of GGA^uA^uDD polyploids, rRNA genes from T. timopheevii and Aegilops tauchii are both active in the F1 hybrids, and still be active in its amphiploids from low generation to the high offspring. The same mechanism, such as DNA methylation which previously acted on rDNA loci in A^u genome, may also act on the newly arrived rDNA loci in A^m genome, resulting in no transcriptional activity of A^m in F₁ hybrids (GA^uA^m).

These findings unveil a novel understanding of the ND associated with allopolyploidization over the evolutionary period of T. zhukovskyi, and highlight certain inactive repeats, such as rDNA units, may serve as the "first reserve" in the form of special chromatin structure to contribute to the successful evolution of polyploid.

 

 

Contact:

Dr. HAN Fangpu

Institute of Genetics and Developmental Biology, Chinese Academy of Sciences

Email: fphan@genetics.ac.cn