Transcriptomics reveals the role of PbCAND2-Ca²⁺ signaling in melatonin-induced disease resistance of Korla fragrant pears

Melatonin (MT) has been demonstrated to participate in modulating disease resistance in postharvest pears. However, the role of the phytomelatonin receptor (PbCAND2)-mediated signaling transduction in this process remains unknown. In this study, MT application reduced disease incidence in stored pear fruit, as indicated by decreased lesion diameter and disease index, accompanied by enhanced total phenolic content, lignin content, and disease-resistant protease activities. MT also activated calcium ion (Ca 2 + ) influx and regulated the levels of calmodulin and calmodulin-like proteins in pear fruit. Concurrently, MT enhanced the activities and transcription levels of MT biosynthesis enzymes and up-regulated the PbCAND2 expression, contributing to elevating the MT level in pear fruit. Further transcriptomic analyses revealed that MT induced disease resistance in pear fruit by stimulating Ca 2+ signaling to modulate amino acid metabolism, carbon metabolism, and biosynthesis of secondary metabolites pathways. Notably, this regulatory effect appears to be mediated by PbCAND2, which molecular docking predicted to interact with PbCIPK4 and PbCML29. Collectively, these findings suggested that MT alleviates black spot disease on Korla fragrant pears via regulating multiple downstream metabolic pathways mediated by PbCAND2-Ca 2+ signaling.