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Evolutionary novelty in gravity sensing through horizontal gene transfer and high-order protein assembly
This study by Nguyen et al. identifies the octahedral crystal matrix protein (OCTIN) as the structural protein that makes up sedimenting vacuolar crystals involved in gravitropism in the fungal order Mucorales (pin molds). OCTIN appears to have originated by horizontal gene transfer from bacteria, retaining elements of the original bacterial assembly mechanism, while acquiring new mutations that increase assembly size to generate crystals vastly larger than the bacterial cells from which the gene was presumably acquired. The image shows fruiting bodies of Phycomyces blakesleeanus, the focus of this study. Each stalk is a single cell that elongates to form a structure 1-3 cm tall, with a spore-containing sphere at its tip. The spores accumulate melanin as they mature, explaining the black color.
Image Credit: Tu Anh Nguyen