@ARTICLE{TreeBASE2Ref22852, author = {Ro Crystal Chaw and Yonghui Zhao and Jie Wei and Nadia Ayoub and Ryan Allen and Kirmanj Atrushi and Cheryl Y. Hayashi}, title = {Intragenic homogenization and multiple copies of prey-wrapping silk genes in Argiope garden spiders}, year = {2014}, keywords = {AcSp1, concerted evolution, intragenic homogenization, multiple loci, silk, spidroin, spider}, doi = {10.1186/1471-2148-14-31}, url = {http://www.biomedcentral.com/1471-2148/14/31}, pmid = {}, journal = {BMC Evolutionary Biology}, volume = {14}, number = {31}, pages = {}, abstract = {BACKGROUND: Spider silks are spectacular examples of phenotypic diversity arising from adaptive molecular evolution. An individual spider can produce an array of specialized silks, with the majority of constituent silk proteins encoded by members of the spidroin gene family. Spidroins are dominated by a central region of tandem repeats flanked by short, non-repetitive N- and C-terminal coding regions. Much of the remarkable mechanical properties of spider silks has been attributed to the repeat sequences. However, the molecular evolutionary processes acting on spidroin terminal and repetitive regions remain unclear due to a paucity of complete gene sequences and sampling of genetic variation among individuals. To gain a better understanding of spider silk evolution, we characterize a complete aciniform spidroin gene from an Argiope orb-weaving spider and survey aciniform gene fragments from congeneric individuals. RESULTS: We present the complete aciniform spidroin (AcSp1) gene from the silver garden spider Argiope argentata (Aar_AcSp1), and document multiple AcSp loci in individual genomes of A. argentata and the congeneric A. trifasciata and A. aurantia. We find that Aar_AcSp1 repeats have >98% pairwise identity at the nucleotide level. By comparing AcSp1 repeat amino acid sequences between Argiope species and with other genera, we identify regions of conservation over vast amounts of evolutionary time. Through a PCR survey of individual A. argentata, A. trifasciata, and A. aurantia genomes, we ascertain that AcSp1 repeats show limited variation between species whereas the terminal regions are more divergent. We also find that average dN/dS across codons in the N-terminal, repetitive, and C-terminal encoding regions indicate purifying selection that is strongest in the N-terminal region. CONCLUSIONS: Using the complete A. argentata AcSp1 gene and spidroin genetic variation between individuals, this study clarifies some of the molecular evolutionary processes underlying the spectacular mechanical attributes of aciniform silk. It is likely that intragenic concerted evolution and functional constraints on A. argentata AcSp1 repeats result in extreme repeat homogeneity. The maintenance of multiple AcSp encoding loci in Argiope genomes supports the hypothesis that Argiope spiders require rapid and efficient protein production to support their prolific use of aciniform silk for prey-wrapping and web-decorating. In addition, multiple gene copies may represent the early stages of spidroin diversification. } }

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