Genome-Wide Identification of SRS Genes and Candidate Regulators of Camptothecin Biosynthesis in Camptotheca acuminata

The SHI-related sequence (SRS) transcription factors are vital plant regulators involved in development and stress responses. Given that biosynthesis of the valuable anticancer drug camptothecin (CPT) in Camptotheca acuminata is influenced by developmental and environmental cues, we hypothesized that SRS genes play key regulatory roles in the CPT biosynthetic pathway. To test this hypothesis and characterize the SRS family in this medicinally crucial plant, we performed a genome-wide identification of CaSRS genes and focused our analysis on their potential functional link to CPT biosynthesis. Eight distinct CaSRS genes were identified and classified into three phylogenetic subgroups. Comprehensive characterization—including phylogenetic relationships, gene structures, conserved motifs, chromosomal distribution, and synteny with Arabidopsis thaliana, Catharanthus roseus, and Ophiorrhiza pumila—provided foundational insights into the family. Crucially, integrated analysis of multi-tissue expression profiles revealed significant correlations between specific CaSRS genes (CaSRS2, CaSRS3, and CaSRS5) and key CPT biosynthetic genes. Promoter cis-regulatory element analysis further indicated that these CaSRS genes possess binding sites associated with stress and hormone responses known to modulate CPT production. These convergent lines of evidence strongly implicate CaSRS2, CaSRS3, and CaSRS5 as potential regulators of CPT biosynthesis. Collectively, this study first identifies specific CaSRS gene candidates for functional validation and provides a crucial foundation for understanding the role of the CaSRS family in regulating CPT biosynthesis in C. acuminata.