Transcriptome analysis of walnut ( Juglans regia L.) fruit reveals the function of JrMYB180 in GA3-induced endocarp lignification

The degree of endocarp lignification in walnut affects its yield, disease resistance, and seed kernel quality. However, its molecular mechanisms have been less studied. Gibberellin A3 (GA 3 ) is widely used as a common chemical regulator in agriculture to regulate lignin synthesis. Our results indicate that 100 mg/L GA 3 accelerated endocarp lignification in the early stages of shell hardenings of “Chandler” walnut. Transcriptome analysis of GA 3 -treated walnut revealed that walnut MYBs are primarily involved in the regulation of GA 3 -induced endocarp lignification. Based on the walnut genome database, we identified 207 MYB family members. By co-expression analysis of the transcriptome, we constructed the regulatory network in the endocarp lignification of walnut and screened the hub gene JrMYB180 , whose expression was greatly induced by exogenous GA 3 . The function of JrMYB180 in the GA 3 -induced lignin biosynthesis in walnut endocarp was further validated by transient over-expression, subcellular localization, and qRT-PCR. This study provides knowledge for studying the development of walnut endocarp and the improvement of walnut varieties.