Homoeolog-specific activation of genes for heat acclimation in the allopolyploid grass Brachypodium hybridum

Abstract

BackgroundAllopolyploid plants often show wider environmental tolerances than their ancestors; this is expected to be due to the merger of multiple distinct genomes with a fixed heterozygosity. The complex homoeologous gene expression could have been evolutionarily advantageous for the adaptation of allopolyploid plants. Despite multiple previous studies reporting homoeolog-specific gene expression in allopolyploid species, there are no clear examples of homoeolog-specific function in acclimation to a long-term stress condition.ResultsWe found that the allopolyploid grass Brachypodium hybridum and its ancestor Brachypodium stacei show long-term heat stress tolerance, unlike its other ancestor, Brachypodium distachyon. To understand the physiological traits of B. hybridum, we compared the transcriptome of the 3 Brachypodium species grown under normal and heat stress conditions. We found that the expression patterns of approximately 26% and approximately 38% of the homoeolog groups in B. hybridum changed toward nonadditive expression and nonancestral expression, respectively, under normal condition. Moreover, we found that B. distachyon showed similar expression patterns between normal and heat stress conditions, whereas B. hybridum and B. stacei significantly altered their transcriptome in response to heat after 3 days of stress exposure, and homoeologs that were inherited from B. stacei may have contributed to the transcriptional stress response to heat in B. hybridum. After 15 days of heat exposure, B. hybridum and B. stacei maintained transcriptional states similar to those under normal conditions. These results suggest that an earlier response to heat that was specific to homoeologs originating from B. stacei contributed to cellular homeostasis under long-term heat stress in B. hybridum.ConclusionsOur results provide insights into different regulatory events of the homoeo-transcriptome that are associated with stress acclimation in allopolyploid plants.

Global analysis of SBP gene family in Brachypodium distachyon reveals its association with spike development

“…Our study also indicates that BdSBP genes contribute thermotolerance during spike development in Brachypodium. Interestingly, differential expression of BdSBP genes in the developing spike under variable temperatures was not been associated with ploidy level in Brachypodium genome as described previously 49 . However, specific expression of these genes in response to high temperature in tetraploid genome, B. hybridum, probably induced by interaction of B. distachyon and B. stacei genomes ( Fig.…”

Polyploid plants have faster rates of multivariate niche differentiation than their diploid relatives

“…In addition, the increased genetic variation of polyploid species may come from rapid and diverse structural genomic changes (Song et al 1995;Chester et al 2012) and the multiple origins of such populations (Ownbey 1950;Werth et al 1985;Brochmann et al 1992;Soltis & Soltis 1999;Doyle et al 2003). Recent analyses of how polyploids respond to abiotic stress (Bardil et al 2011;Akama et al 2014;Paape et al 2016;Takahagi et al 2018) suggest this variation is important for polyploid establishment and that it may play a role in the climatic niche differences we observed. Previous analyses of niche differentiation in polyploid species found less consistent patterns (Felber-Girard et al 1996;Petit & Thompson 1999;Martin & Husband 2009;Glennon et al 2014;Marchant et al 2016).…”

Brachypodium: A Monocot Grass Model Genus for Plant Biology

“…The three annual Brachypodium species were selected as a tractable grass polyploid system to 522 investigate the effects of subgenome dominance and origin in the phenotypic, physiological and adaptive 523 responses of the allotetraploid hybrids (Catalán et al, 2016a;Gordon et al, 2016;Takahagi et al, 2018) 524 (Table 2). These species are the allotetraploid B. hybridum and its diploid parents B. stacei and B.…”