Abstract: Here we report on the cloning and characterization of BhC2DP1, a novel gene encoding a plant-specific small protein with a single C2 domain from the resurrection plant Boea hygrometrica. Phylogenic analysis of C2-domain proteins and sequence analysis revealed that BhC2DP1 belongs to the C2 elicitor responsive protein subfamily. Real-time PCR and histochemical study of a GUS reporter gene driven by the BhC2DP1 promoter in transgenic Arabidopsis showed BhC2DP1 transcripts increased at the early stage after dehydration and exposure to exogenous Ca²⁺ but decreased with prolonged treatment. Expression of BhC2DP1 was suppressed by abscisic acid (ABA) and Ca²⁺-chelating agent EGTA but was promoted by simultaneous exposure to ABA and EGTA, suggesting that the transcriptional regulation of BhC2DP1 by ABA is Ca²⁺ dependent. Constitutive overexpression of BhC2DP1 in Arabidopsis resulted in an ABA-hypersensitive phenotype, which was rescued by supplementing EGTA to growth media. Therefore, Ca²⁺ is necessary for the function of BhC2DP1 in responding to ABA. Our results provide new insights into the role of small C2-domain proteins and the fine-tuning regulation mechanism in response to drought stress.