Abstract
Dehydration proteins (dehydrins, DHNs) confer tolerance to water-stress deficit in plants. We performed a comparative genomics and evolutionary study of DHN genes in four model Brachypodium grass species. Due to limited knowledge on dehydrin expression under water deprivation stress in Brachypodium, we also performed a drought-induced gene expression analysis in 32 ecotypes of the genus’ flagship species B. distachyon showing different hydric requirements. Genomic sequence analysis detected 10 types of dehydrin genes (Bdhn) across the Brachypodium species. Domain and conserved motif contents of peptides encoded by Bdhn genes revealed eight protein architectures. Bdhn genes were spread across several chromosomes. Selection analysis indicated that all the Bdhn genes were constrained by purifying selection. Three upstream cis-regulatory motifs (BES1, MYB124, ZAT) were detected in several Bdhn genes. Gene expression analysis demonstrated that only four Bdhn1-Bdhn2, Bdhn3, and Bdhn7 genes, orthologs of wheat, barley, rice, sorghum, and maize genes, were expressed in mature leaves of B. distachyon and that all of them were more highly expressed in plants under drought conditions. Brachypodium dehydrin expression was significantly correlated with drought-response phenotypic traits (plant biomass, leaf carbon and proline contents and water use efficiency increases, and leaf water and nitrogen content decreases) being more pronounced in drought-tolerant ecotypes. Our results indicate that dehydrin type and regulation could be a key factor determining the acquisition of water-stress tolerance in grasses.
Highlights
Water deprivation is one of the main abiotic stresses that affect plant development and fitness [1,2]
Genome searches in Phytozome and Ensembl Plants retrieved 47 dehydrin gene sequences collected from the reference genomes of the four sequenced Brachypodium species [B. distachyon Bd21 2n = 2x = 10, x = 5 (10); B. sylvaticum Ain-1 2n = 2x = 18, x = 9 (10); B. stacei ABR114 2n = 2x = 20, x = 10 (9); B. hybridum ABR113 2n = 4x = 30, x = 5 + 10 (18; 9 from its B. distachyon-type D subgenome and 9 from its B. stacei-type S subgenome)] (Table 1; Figure 1b)
A total of 54 orthologous DHN sequences were retrieved from the reference genomes of six outgroup grass species [Aegilops tauschii 2n = 2x = 14, x = 7 (9); Hordeum vulgare 2n = 2x = 14, x = 7 (8); Zea mays 2n = 2x = 20, x = 10 (7); Oryza sativa 2n = 2x = 24, x = 12 (6); Sorghum bicolor 2n = 2x = 20, x = 10 (5); Triticum aestivum 2n = 6x = 42, x = 7 (19); Supplementary Table S1]
Summary
Water deprivation is one of the main abiotic stresses that affect plant development and fitness [1,2]. Dehydrins (DHN) belong to group 2 LEA (Late-Embryogenesis-Abundant) proteins [7], and are intrinsically disordered hydrophilic proteins that acquire structure when bound to ligands, such as membranes, acting as chaperones that impede the aggregation or inactivation of other proteins under desiccation to maintain the biological activity of the cell [8,9]. They show a high hydration capacity and can bind large quantities of cations, retaining water in the drying cells and preventing ionic unbalance and protein denaturation. DHNs accumulate in all vegetative tissues under water stress, though with different specificities [4], as well as during seed development [8]
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