Browsing by Author "Melkonian, M"
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Item Open Access Horizontal transfer of an adaptive chimeric photoreceptor from bryophytes to ferns.(Proceedings of the National Academy of Sciences of the United States of America, 2014-05) Li, F; Villarreal, JC; Kelly, S; Rothfels, CJ; Melkonian, M; Frangedakis, E; Ruhsam, M; Sigel, EM; Der, JP; Pittermann, JFerns are well known for their shade-dwelling habits. Their ability to thrive under low-light conditions has been linked to the evolution of a novel chimeric photoreceptor--neochrome--that fuses red-sensing phytochrome and blue-sensing phototropin modules into a single gene, thereby optimizing phototropic responses. Despite being implicated in facilitating the diversification of modern ferns, the origin of neochrome has remained a mystery. We present evidence for neochrome in hornworts (a bryophyte lineage) and demonstrate that ferns acquired neochrome from hornworts via horizontal gene transfer (HGT). Fern neochromes are nested within hornwort neochromes in our large-scale phylogenetic reconstructions of phototropin and phytochrome gene families. Divergence date estimates further support the HGT hypothesis, with fern and hornwort neochromes diverging 179 Mya, long after the split between the two plant lineages (at least 400 Mya). By analyzing the draft genome of the hornwort Anthoceros punctatus, we also discovered a previously unidentified phototropin gene that likely represents the ancestral lineage of the neochrome phototropin module. Thus, a neochrome originating in hornworts was transferred horizontally to ferns, where it may have played a significant role in the diversification of modern ferns.Item Open Access Phytochrome diversity in green plants and the origin of canonical plant phytochromes(Nature communications, 2015) Li, F; Melkonian, M; Rothfels, CJ; Villarreal, JC; Stevenson, DW; Graham, SW; Wong, GK; Pryer, KM; Mathews, SItem Open Access Phytochrome diversity in green plants and the origin of canonical plant phytochromes.(Nat Commun, 2015-07-28) Melkonian, M; Pryer, KM; Rothfels, CJ; Graham, SW; Li, F; Villarreal, JC; Wong, GK; Stevenson, DW; Mathews, SPhytochromes are red/far-red photoreceptors that play essential roles in diverse plant morphogenetic and physiological responses to light. Despite their functional significance, phytochrome diversity and evolution across photosynthetic eukaryotes remain poorly understood. Using newly available transcriptomic and genomic data we show that canonical plant phytochromes originated in a common ancestor of streptophytes (charophyte algae and land plants). Phytochromes in charophyte algae are structurally diverse, including canonical and non-canonical forms, whereas in land plants, phytochrome structure is highly conserved. Liverworts, hornworts and Selaginella apparently possess a single phytochrome, whereas independent gene duplications occurred within mosses, lycopods, ferns and seed plants, leading to diverse phytochrome families in these clades. Surprisingly, the phytochrome portions of algal and land plant neochromes, a chimera of phytochrome and phototropin, appear to share a common origin. Our results reveal novel phytochrome clades and establish the basis for understanding phytochrome functional evolution in land plants and their algal relatives.Item Open Access The Origin and Evolution of Phototropins(2015) Rothfels, CJ; Wong, GK; Stevenson, DW; Li, F; Mathews, S; Melkonian, M; Pryer, KM; Graham, SW; Villarreal, JCItem Open Access The origin and evolution of phototropins.(Front Plant Sci, 2015) Li, F; Rothfels, CJ; Melkonian, M; Villarreal, JC; Stevenson, DW; Graham, SW; Wong, GK - S; Mathews, S; Pryer, KMPlant phototropism, the ability to bend toward or away from light, is predominantly controlled by blue-light photoreceptors, the phototropins. Although phototropins have been well-characterized in Arabidopsis thaliana, their evolutionary history is largely unknown. In this study, we complete an in-depth survey of phototropin homologs across land plants and algae using newly available transcriptomic and genomic data. We show that phototropins originated in an ancestor of Viridiplantae (land plants + green algae). Phototropins repeatedly underwent independent duplications in most major land-plant lineages (mosses, lycophytes, ferns, and seed plants), but remained single-copy genes in liverworts and hornworts-an evolutionary pattern shared with another family of photoreceptors, the phytochromes. Following each major duplication event, the phototropins differentiated in parallel, resulting in two specialized, yet partially overlapping, functional forms that primarily mediate either low- or high-light responses. Our detailed phylogeny enables us to not only uncover new phototropin lineages, but also link our understanding of phototropin function in Arabidopsis with what is known in Adiantum and Physcomitrella (the major model organisms outside of flowering plants). We propose that the convergent functional divergences of phototropin paralogs likely contributed to the success of plants through time in adapting to habitats with diverse and heterogeneous light conditions.