Genome-Wide Characterization and Expression Analysis of <i>CBP60</i> Gene Family in <i>Citrullus lanatus</i> in Response to <i>Fusarium oxysporum</i> Infection and Aphid Infestation

The <i>calmodulin-binding protein 60</i> (<i>CBP60</i>) family comprises essential Ca²⁺-responsive transcription factors that orchestrate salicylic acid (SA)-mediated immunity and broader stress responses. Despite being extensively characterized in model species, the <i>CBP60</i> family remains poorly understood in watermelon (<i>Citrullus lanatus</i>), a globally significant cucurbit crop highly susceptible to aphid infestation and fusarium wilt. In this study, we performed a comprehensive genome-wide identification and characterization of the <i>CBP60</i> gene family in watermelon, identifying 16 putative <i>ClaCBP60</i> members, all of which harbor the conserved calmodulin-binding domain. These genes are non-randomly distributed across chromosomes, featuring a prominent cluster of 10 members on chromosome 3. Phylogenetic analysis across seven cucurbit species categorized the CBP60 proteins into four distinct subfamilies, revealing both evolutionary conservation and lineage-specific diversification. Gene structure and conserved motif analyses revealed shared core domains with subfamily-specific variations, indicative of functional divergence. Furthermore, synteny analysis showed strong collinearity with cucumber and melon, reflecting the evolutionary stability of key <i>CBP60</i> loci. Transcriptional profiling under <i>F. oxysporum</i> infection and aphid infestation revealed dynamic expression patterns, with <i>ClaCBP60_01</i> and <i>ClaCBP60_16</i> exhibiting rapid and robust induction during the early stages of both stresses. These findings indicated that <i>ClaCBP60</i> genes operate in a coordinated yet diversified manner to modulate defense signaling against <i>F. oxysporum</i> and aphid attack. This study provides a systematic insight into <i>CBP60</i> family members in watermelon, establishing a foundation for validation and molecular breeding aimed at enhancing biotic tolerance.