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

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.