Tests of the link between functional innovation and positive selection at phytochrome a: The phylogenetic distribution of far-red high-irradiance responses in seedling development

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We surveyed the phylogenetic distribution of far-red high-irradiance responses (FR-HIRs), which are important for early development of seedlings in shaded habitats, in exemplar species across seed plants to test whether the responses are unique to angiosperms and may have helped early angiosperms colonize the understory of Mesozoic forests dominated by ferns and gymnosperms. We show that dark-grown seedlings in most seed plants adopt an etiolated morphology and that being green in the dark is a derived condition in some conifers and gnetophytes. We also show that FR-HIR-induced seedling de-etiolation, mediated by phytochrome, is widely distributed in seed plants. Together, these data show that despite the ability of gymnosperms to green in the dark, most of them do not do so but link seedling development to light signals, as do angiosperms. Our data refute an obvious link between the origin of FR-HIRs and the signal of positive selection at the PHYA locus early in the history of angiosperms. © 2012 by The University of Chicago. All rights reserved.

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International Journal of Plant Sciences

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