ClWRKY75 regulates lignin biosynthesis to confer Colletotrichum fructicola resistance in watermelon.

Watermelon, a significant horticultural crop, is threatened by various fungal diseases throughout its growth cycle, with Colletotrichum fructicola, a member of the Colletotrichum spp., being notorious for causing anthracnose, which damages both seedlings and fruits. Anthracnose control mainly depends on fungicides, while resistant watermelon breeding is hindered by scarce resistance genes and unclear molecular mechanisms. Here we show that the WRKY transcription factor ClWRKY75 was strongly induced in the resistant line M10 following Colletotrichum fructicola infection by comparative transcriptomic analysis. Silencing ClWRKY75 through virus-induced gene silencing (VIGS) converted resistant M10 plants into a susceptible phenotype, accompanied by reduced lignin accumulation. We further demonstrate that ClWRKY75 directly binds to and activates the promoter of ClPAL20, a key gene in the lignin biosynthetic pathway. These results reveal that ClWRKY75 enhances anthracnose resistance by promoting lignin synthesis, and offer useful gene resources for resistant watermelon breeding.