Comparative analyses on the structure, composition, and gene expression in seed coat of hulled and hull-less lines in Cucurbita moschata

Abstract The escalating demand for hull-less Cucurbita moschata seeds, driven by a thorough comprehensive understanding of their functional properties and the global trade in pumpkin seeds, emphasizes the necessity to expedite the breeding of hull-less varieties to satisfy market requirements. Existing knowledge regarding hull-less seeds in pumpkins primarily stems from studies on C. pepo , where the lignin pathway is considered a significant factor; however, its significance in C. moschata remains unexplored. This study aims to investigate anatomical, compositional, and gene expression alterations in the seed coat of one hulled wild type (RHS-1) and three hull-less mutant recombinant inbred lines (RHLS-2, RHLS-3 and RHLS-4) at 20 DPA (days post anthesis) and 50 DPA in C. moschata . The anatomical changes in the seed coat of hulled and hull-less lines in C. moschata during seed coat development were comparable to those observed in C. pepo , with five distinct seed coat layers appearing in the hulled wild type but a papery thin layer (composed of the epidermis and sclerenchyma) in the hull-less mutants. However, compositional changes in pectin content in the seed coat of hulled and hull-less lines in C. moschata differed from those in C. pepo . Specifically, the seed coat of hull-less mutants exhibited higher pectin levels than that of hulled wild type. Additionally, the expression of three lignin biosynthesis genes ( CmoC4H, Cmo4CL , and CmoCCR ) was upregulated at 50 DPA, which was contrary to the patterns observed in C. pepo . In summary, our results revealed both conserved and distinct features of the seed coat development between C. moschata and C. pepo . These correlative findings provide comparative features of seed coat development in hulled and hull-less C. moschata lines and provide candidate genes for future functional studies.