Abstract only

Wheat, one of the world?s most important crops , and its related species are well known to have evolved through allopolyploidizations, which are widely found in the plant kingdom. Common wheat, Triticum aestivum (2n=6x=42; genome formula AABBDD), originated about 10,000 years ago from hybridization between a domesticated tetraploid form, T. turgidum (2n=4x=28, AABB), and goat grass, Aegilops tauschii (2n=2x=14, DD). In this study, global gene expression patterns in two combinations of synthesized triploids and their amphidiploids were compared to understand the genome-wide change of gene expressions during the course of amphidiploidization. A 38K oligo- DNA microarray (Agilent Technologies) was used to compare transcriptional changes between the parents, synthesized triploids, and their amphidiploidized hexaploids. Two combinations of triploids (ABD) were synthesized by crossing, and their amphidiploidized hexaploids (AABBDD) were maintained through long-term self-pollinations. Total RNAs were extracted from seedlings of these two lines for hybridization with the DNA microarray. In total, 25,926 gene probes in the DNA microarray showed reliable expression signals based on quality control and normalization. When whole transcriptomic differences were analyzed in the same species between two parental lines, 86% and 78% of the expressed genes in the maternal and paternal parents, respectively, showed identical expression. Therefore, the overall transcriptomes of each pair of parental species were similar. Synthetic polyploid expression levels were compared with mid-parent values (MPVs) averaged from the parental species to estimate the nonadditive gene expression patterns. Equal expression with MPVs was termed ?additive expression?; all others were defined as ?nonadditive expression.? The majority of the expressed genes showed additive expression compared to the corresponding MPVs in both combinations. A large number of the additively expressed genes in triploids remained unchanged after amphidiploidization (17,576 genes in combination 1 and 22,387 genes in combination 2, P<0.01) suggesting that additive expression in triploids is stably inherited after amphidiploidization. The nonadditive expression changes seen from the synthetic triploid to the hexaploid during amphidiploidization differed between the two combinations, but the nonadditive expressed genes of the synthetic polyploids showed a tetraploid parental dominance expression pattern in both combinations. Thus, nonadditive expression genes are strongly affected by the tetraploid maternal parent. Gene Ontology (GO) analysis was conducted for each combination, the synthetic triploids, and their amphidiploids to investigate the possible functional relevance of the non-additively expressed genes. These genes were involved in diverse functional categories. These results show the global changes in gene expression occurring during amphidiploidization, as demonstrated by speciation in Triticum aestivum.

Global Wheat Program

English

Lucia Segura

INT2678

CIMMYT Staff Publications Collection