Mapping and transcriptomic profiling reveal that the KNAT6 gene is involved in the dark green peel colour of mature pumpkin fruit (Cucurbita maxima L.).

key messageWe identified a 580 bp deletion of CmaKNAT6 coding region influences peel colour of mature Cucurbita maxima fruit. Peel colour is an important agronomic characteristic affecting commodity quality in Cucurbit plants. Genetic mapping of fruit peel colour promotes molecular breeding and provides an important basis for understanding the regulatory mechanism in Cucurbit plants. In the present study, the Cucurbita maxima inbred line '9-6' which has a grey peel colour and 'U3-3-44' which has a dark green peel colour in the mature fruit stage, were used as plant materials. At 5-40 days after pollination (DAP), the contents of chlorophyll a, chlorophyll b, total chlorophyll and carotenoids in the 'U3-3-44' peels were significantly greater than those in the '9-6' peels. In the epicarp of the '9-6' mature fruit, the presence of nonpigmented cell layers and few chloroplasts in each cell in the pigmented layers were observed. Six generations derived by crossing '9-6' and 'U3-3-44' were constructed, and the dark green peel was found to be controlled by a single dominant locus, which was named CmaMg (mature green peel). Through bulked-segregant analysis sequencing (BSA-seq) and insertion-deletion (InDel) markers, CmaMg was mapped to a region of approximately 449.51 kb on chromosome 11 using 177 F