Drought stress significantly hampers plant growth and productivity. Strigolactones (SLs), a class of carotenoid-derived plant hormones, are recognized for their pivotal role in modulating plant morphology and enhancing drought resistance. Nonetheless, the underlying mechanisms through which SLs influence drought tolerance in tall fescue remain largely unexplored. In this study, we employed TIS108 to inhibit SL biosynthesis under drought conditions and assessed a range of morphological and physiological parameters in tall fescue, including biomass both above and below ground, antioxidase activities, proline and soluble sugar contents, and survival rates, across treatments of drought and drought coupled with TIS108 inhibition. Our findings demonstrate that the suppression of SL synthesis detrimentally affects the drought resilience of tall fescue. Through comprehensive transcriptome sequencing and subsequent qRT-PCR analyses of samples subjected to drought with and without TIS108 treatment, we identified a marked downregulation of genes involved in auxin metabolism and root development. This downregulation correlated with significant reductions in total root length, root surface area, and the number of root tips under drought stress conditions. Collectively, our research elucidates that the inhibition of SL synthesis impairs drought tolerance in tall fescue by constraining root growth and development, mediated through the modulation of auxin metabolism.

Plant height and tillering are the key traits of tall fescue (Festuca arundinacea Schreb.), a perennial turf grass widely used for forage and turf worldwide. It exhibits excellent abiotic stress tolerance. However, the investigation of these traits at the genetic level is limited by the lack of a completely sequenced genome of tall fescue. Here, we generated genome-wide transcriptome data using PacBio isoform sequencing (Iso-Seq) technology. We obtained 73,628 transcripts with an average length of 2410 bp. Among these transcripts, 42,265 (60.09%) were predicted as complete full-length open reading frames. The dataset contained 11,520 simple sequence repeats; 737 bp long non-coding RNAs; and 1599 alternative splicing sites in unigenes. Sixty-three unigenes involved in abscisic acid biosynthesis, catabolism, and signaling pathways were identified. The Illumina-sequencing analysis results, further verified using qRT-PCR, revealed the significant upregulation of nine unigenes under drought stress. Ninety-three unigenes involved in controlling plant height and tillering were also identified, of which FaMAX1 was functionally verified to regulate plant tillering. Our results provide a valuable genetic resource about the complete transcriptome of tall fescue; the identified candidate genes can aid in improving the drought tolerance and agronomic traits in tall fescue and other related plants.