Citrus is one of the most economically important fruit crops worldwide, with an annual production exceeding 150 million tons. However, its production is severely constrained by anthracnose caused primarily by Colletotrichum gloeosporioides , the dominant and most destructive fungal pathogen leading to heavy losses in both field and post-harvest stages. Serine carboxypeptidase-like (SCPL) proteins play crucial roles in plant stress responses, but their functions in citrus-pathogen interactions remain poorly understood. In this study, we identified and characterized SCPL genes in three citrus species: 41 in Citrus sinensis , 49 in Citrus clementina , and 35 in Poncirus trifoliata . Phylogenetic analysis classified these genes into three clades, with distinct motif compositions and exon-intron structures. Promoter analysis identified a suite of stress-responsive elements in the CsSCPL genes, alongside abundant light- and hormone-responsive elements, supporting their potential role in stress response signaling pathways. Transcriptomic profiling during C. gloeosporioides infection identified seven upregulated and four downregulated CsSCPL genes. Among five candidate genes, functional validation via transient overexpression demonstrated that CsSCPL36 significantly enhanced disease resistance, reducing lesion area and fungal biomass compared to controls. Further mechanistic investigation revealed that CsSCPL36 activated both salicylic acid (SA)- and jasmonic acid (JA)-mediated defense pathways, upregulating the expression of pathogenesis-related genes ( CsPR1 , CsPR3 , CsPR4 , CsPR5 ). In addition, CsSCPL36 overexpression markedly enhanced the activity of ROS-scavenging enzymes including CAT, POD and SOD under pathogen challenge. Our findings provide novel insights into the role of the CsSCPL gene family in citrus defense and identify CsSCPL36 as a key molecular target for manipulating and improving fungal resistance. • Genome-wide identification of SCPL genes across three citrus species revealed an expansion of this gene family and pinpointed eleven genes responsive to fungal infection, with seven being up-regulated and four down-regulated. • Functional validation showed that CsSCPL36 significantly enhanced anthracnose resistance, reducing lesion area and fungal biomass in citrus. • CsSCPL36 activated both SA/JA defense pathways (upregulating CsPR1/3/4/5) and enhanced ROS-scavenging enzyme (CAT, POD, SOD) activity under pathogen stress.
He et al. (Wed,) studied this question.