Flavonoid-Mediated Sex-Specific Fluorescence in Silkworm Cocoons: A Strain-Restricted Trait

Flavonoids have been implicated in the formation of sex-discriminating fluorescent silkworm cocoons. However, their specific composition in these cocoons remain unexplored. In this study, flavonoid-targeted metabolomics was employed to profile the flavonoid composition of a sex-dependent fluorescent silkworm cocoon strain. Our results revealed comparable total flavonoid content between the violet and yellow fluorescent cocoons, but markedly different flavonoid composition, particularly in a subclass of flavonols. Moreover, four differential flavonoids, baimaside, luteolin-3′,7-di-O-glucoside, quercetin 3,7-diglucoside, and spiraeoside, were identified, among which quercetin 3,7-diglucoside, the most abundant, with levels exceeding the others by an order of magnitude, emerged as the most promising biomarker for the sex-dependent fluorescent phenotypes. These findings pave the way for future investigations into the molecular basis of sex-dependent fluorescent cocoon formation and support the breeding of sex-discriminating fluorescent cocoons for high-quality silk production.