Conservation of Genomic Imprinting during Wheat Polyploidization

Yang et al. discover conservation of genomic imprinting between closely related Triticum and Aegilops species.

By Guanghui Yang and Mingming Xin

Background: Genomic imprinting causes genes to be differentially expressed depending on their parent-of-origin, which mainly occurs in the endosperm of plants. Researchers have identified hundreds of imprinted genes in plants by using RNA-seq methods. However, the conservation of imprinted genes among different plant species is still debatable. We investigated the evolutionary conservation of imprinted genes in diploid wheat (DD, Aegilops tauschii), tetraploid wheat (AABB, Triticum turgidum), and hexaploid wheat (AABBDD, Triticum aestivum) during the hexaploidization history.

Question: Is genomic imprinting evolutionarily conserved during wheat polyploidization? We tested this by performing high-throughput sequencing analysis of hybrid endosperm from reciprocal crosses at different developmental stages.

Findings: We found that genomic imprinting was evolutionarily conserved between closely related Triticum and Aegilops species, and in the face of polyploid hybridization between species in these genera. Nearly half of the imprinted genes exhibited conserved expression patterns during wheat hexaploidization. In addition, forty percent of the homeolog pairs originating from whole genome duplication were consistently maternally or paternally biased in the different subgenomes of hexaploid wheat. Furthermore, imprinted expression was found for 41.2% and 50.0% of homolog pairs that evolved by tandem duplication after genome duplication in tetraploid and hexaploid wheat, respectively.

Next steps: Although many imprinted genes were identified, their biological functions are still largely unknown. Next we will try to understand why and how genomic imprinting is conserved in wheat species during wheat polyploidization and the potential function during wheat endosperm development.

Guanghui Yang, Zhenshan Liu, Lulu Gao, Kuohai Yu, Man Feng, Yingyin Yao, Huiru Peng, Zhaorong Hu, Qixin Sun, Zhongfu Ni, and Mingming Xin (2017). Genomic Imprinting was Evolutionarily Conserved during Wheat Polyploidization. Plant Cell 30: 37-47