Genome-wide characterization of early response genes to abscisic acid coordinating multiple pathways in Aegilops tauschii

The diploid wild goat grass Aegilops tauschii (Ae. tauschii, 2n = 14; DD), as the D-sub genome of common wheat, provides rich germplasm resources for many aspects of wheat breeding. Abscisic acid (ABA) is an essential phytohormone that plays a pivotal role in plant adaptation to abiotic stresses. However, the gene regulation network of Ae. tauschii in response to ABA stress remains unclear. Here, we conducted a time-course strand-specific RNA-sequencing study to globally profile the transcriptome that responded to ABA treatment in Ae. tauschii. We identified 4818 differentially expressed transcription units/genes with time-point-specific induction/repression patterns. Using functional annotation, one-to-one ortholog and comparative transcriptome profiling analyses, we identified 319 ABA-responsive Ae. tauschii orthologs that were also induced/repressed under ABA treatment in hexaploid wheat. On the quantitative trait loci (QTL) used in wheat marker-assisted breeding, we found that the ABA-responsive expression patterns of eight Ae. tauschii orthologs were associated with drought stress tolerance, flowering process and/or grain quality. Of them, the ABA-responsive gene encoding sucrose:sucrose 1-fructosyltransferase in fructan and glucose metabolism pathways showed the most significant association with wheat drought tolerance. The characterization of ABA early-responsive genes in this study provides valuable information for exploring the molecular functions of the regulatory genes and will assist in wheat breeding.