PubMed · 2026-06-15
Watermelon plants naturally boost their own melatonin levels when aphids attack, and this melatonin triggers a calcium-based alarm signal that activates the plant's defenses. Scientists identified the specific molecular players — a calcium channel (CNGC20) and a regulatory protein (CaM7) — that control how strong this defense response becomes.
Aphid infestation significantly upregulated the melatonin biosynthetic gene ClCOMT1 and raised melatonin levels in watermelon; overexpressing ClCOMT1 enhanced aphid resistance, while knocking it out had the opposite effect.
The calcium channel ClCNGC20 is required for melatonin-induced cytosolic calcium accumulation and aphid resistance — silencing it blocked both effects, while overexpressing it in Arabidopsis raised calcium levels and improved resistance.
Calmodulin 7 (ClCaM7) physically interacts with ClCNGC20 and suppresses its activity, acting as a negative regulator; silencing ClCaM7 restored calcium accumulation and aphid resistance in melatonin-deficient mutants.
