Making the Bread: Insights from Newly Synthesized Allohexaploid Wheat.
Bread wheat (or common wheat, Triticum aestivum) is an allohexaploid (AABBDD, 2n = 6x = 42) that arose by hybridization between a cultivated tetraploid wheat T. turgidum (AABB, 2n = 4x = 28) and the wild goatgrass Aegilops tauschii (DD, 2n = 2x = 14). Polyploidization provided niches for rigorous genome modification at cytogenetic, genetic, and epigenetic levels, rendering a broader spread than its progenitors. This review summarizes the latest advances in understanding gene regulation mechanisms in newly synthesized allohexaploid wheat and possible correlation with polyploid growth vigor and adaptation. Cytogenetic studies reveal persistent association of whole-chromosome aneuploidy with nascent allopolyploids, in contrast to the genetic stability in common wheat. Transcriptome analysis of the euploid wheat shows that small RNAs are driving forces for homoeo-allele expression regulation via genetic and epigenetic mechanisms. The ensuing non-additively expressed genes and those with expression level dominance to the respective progenitor may play distinct functions in growth vigor and adaptation in nascent allohexaploid wheat. Further genetic diploidization of allohexaploid wheat is not random. Regional asymmetrical gene distribution, rather than subgenome dominance, is observed in both synthetic and natural allohexaploid wheats. The combinatorial effects of diverged genomes, subsequent selection of specific gene categories, and subgenome-specific traits are essential for the successful establishment of common wheat.
National Key Facility for Crop Gene Resources and Genetic Improvement, Institute of Crop Science, Chinese Academy of Agricultural Sciences, Beijing 100081, China.
Ai-li
AL
Li
National Key Facility for Crop Gene Resources and Genetic Improvement, Institute of Crop Science, Chinese Academy of Agricultural Sciences, Beijing 100081, China.
Shuai-Feng
SF
Geng
Triticeae Research Institute, Sichuan Agricultural University, Chengdu, Sichuan 611130, China.
Lian-quan
LQ
Zhang
Triticeae Research Institute, Sichuan Agricultural University, Chengdu, Sichuan 611130, China.
Deng-cai
DC
Liu
National Key Facility for Crop Gene Resources and Genetic Improvement, Institute of Crop Science, Chinese Academy of Agricultural Sciences, Beijing 100081, China. Electronic address: maolong@caas.cn.
Long
L
Mao
D001939:Bread / Q000032:analysis*; D005813:Genes, Synthetic; D018745:Genome, Plant; D006824:Hybridization, Genetic; D011123:Polyploidy; D014908:Triticum / Q000235:genetics*
adaptation; allopolyploidy; expression level dominance; heterosis; synthetic wheat