Genome-wide identification, characterization and expression analysis of the subtilisin-like protease gene family in Quercus ilex in response to Phytophthora cinnamomi

Subtilisin-like proteases (SBTs) are a large family of serine peptidases involved in diverse biological processses, including plant stress responses, but remain poorly characterized in forest trees. In this study, we report the genome-wide identification and characterization of the SBT gene family in Quercus ilex (QiSBT), with a focus on their transcriptional organization and response to Phytophthora cinnamomi infection. A total of 87 QiSBT genes were identified, structurally annotated, and phylogenetically classified into seven subfamilies based on comparative analyses with Arabidopsis thaliana, Populus trichocarpa, and three other Quercus species (Q. lobata, Q. robur, and Q. variabilis). Analyses of conserved domains and gene structures revealed a high degree evolutionary conservation, with one subfamily enriched in intronless or intron-poor genes. Promoter analysis identified numerous stress- and hormone-responsive cis-elements, suggesting potential transcriptional regulation under environmental stress conditions. Expression profiling under P. cinnamomi infection revealed differential transcriptional responses within the QiSBT gene family. In particular, QiSBT24, QiSBT63, and QiSBT69 showed significant induction in inoculated seedlings, with approximate 3-, 8-, and 30-fold, respectively. These results provide new insights into the structure, evolution, and potential defense-related roles of SBTs in Q. ilex, offering a foundation for future functional aimed at understanding their contribution to resistance mechanisms in Mediterranean oak species.