Genome-wide analysis of the GRAS family and its transcriptional response to strigolactone during post-drought recovery in elephant grass

Background Strigolactones (SL) are pivotal in shaping root system architecture to aid drought acclimation; yet, the transcriptional landscapes underpinning this response in elephant grass ( Cenchrus purpureus ) remain elusive. While the GRAS transcription factor family is established as a regulator of plant development, its evolutionary trajectory and transcriptional behaviour in response to SL under water-deficit conditions have not been explored in this species. Results We identified 126 CpGRAS genes classified into 12 subfamilies. Among them, LISCL and PAT1 were the most expanded, whereas DLT, SCL4/7, and unknown1 contained the fewest members. Chromosomal distribution analysis indicated that the expansion of this family was primarily driven by whole-genome duplication events. While most members exhibited strong purifying selection (Ka/Ks < 1), the LISCL and HAM subfamilies displayed relatively higher divergence. Promoter analysis revealed a widespread enrichment of cis-elements responsive to abscisic acid (ABA), jasmonic acid (JA), gibberellin (GA), and drought stress. Through comparative transcriptomic profiling of roots subjected to 14 days of drought stress and sampled 14 h after a single SL application during re-watering, we found that SL treatment was associated with a distinct upregulation of the PAT1 ( CpGRAS30-4 ), HAM ( CpGRAS22-2/22-6 ), SCR ( CpGRAS28-4 ), and SCL4/7 ( CpGRAS32-1 ) subfamilies. Furthermore, RNA in situ hybridisation localised CpGRAS32-1 expression to the vascular cylinder, particularly the pericycle, and lateral root primordia, with markedly enhanced signal intensity following SL treatment. Conclusions Our study presents a genome-wide survey of the CpGRAS family, underscoring its polyploidy-driven expansion and stress-responsive potential. The responsiveness of specific subfamilies to SL treatment, particularly the precise spatial regulation of CpGRAS32-1 , implicates these transcription factors as putative components of the SL-associated transcriptional network in root adaptation. These findings highlight promising candidates for genetic improvement of drought resilience in forage crops.