The three novel complete aciniform spidroin variants from Araneus ventricosus reveal diversity of gene sequences within specific spidroin type

Orb-weaving spiders produce multiple types of silks with distinct functions and material features, and all these silks are mainly composed of proteins which encoded by specific spidroin (spider silk protein) gene family members. Moreover, nearly all spidroins have evolved one or more variants within specific-species. However, the majority of variant sequences are fragmentary, limiting us to investigate the molecular structures and evolution relationships between spidroin variant genes. As the silk that is used to wrap prey and form an egg case liner, aciniform silk is given high toughness and tensile strength. To date, only one aciniform spidroin 1 (AcSp1) gene sequence from orb weavers Araneus ventricosus was reported, and it is still unknown whether presence of multiple AcSp1 variants in this species. Here, we present three novel complete AcSp1 variant gene sequences from Araneus ventricosus. The primary structures revealed the varying length of these variants, and partial repetitive sequences of two AcSp1 variants were deleted. Phylogenetic analysis showed AcSp1 seems to undergo multiple rounds of gene duplication, and the AcSp1-v4 likely originates from a recent duplication event. In brief, the generation of multiple AcSp1 variant genes contributes to transcript diversification and could result in varying tensile properties of aciniform silks.