The angiosperm order Malpighiales includes ∼16,000 species and constitutes up to 40% of the understory tree diversity in tropical rain forests. Despite remarkable progress in angiosperm systematics during the last 20 y, relationships within Malpighiales remain poorly resolved, possibly owing to its rapid rise during the mid-Cretaceous. Using phylogenomic approaches, including analyses of 82 plastid genes from 58 species, we identified 12 additional clades in Malpighiales and substantially increased resolution along the backbone. This greatly improved phylogeny revealed a dynamic history of shifts in net diversification rates across Malpighiales, with bursts of diversification noted in the Barbados cherries (Malpighiaceae), cocas (Erythroxylaceae), and passion flowers (Passifloraceae). We found that commonly used a priori approaches for partitioning concatenated data in maximum likelihood analyses, by gene or by codon position, performed poorly relative to the use of partitions identified a posteriori using a Bayesian mixture model. We also found better branch support in trees inferred from a taxon-rich, data-sparse matrix, which deeply sampled only the phylogenetically critical placeholders, than in trees inferred from a taxon-sparse matrix with little missing data. Although this matrix has more missing data, our a posteriori partitioning strategy reduced the possibility of producing multiple distinct but equally optimal topologies and increased phylogenetic decisiveness, compared with the strategy of partitioning by gene. These approaches are likely to help improve phylogenetic resolution in other poorly resolved major clades of angiosperms and to be more broadly useful in studies across the Tree of Life. M alpighiales are one of the most surprising clades discovered in broad molecular phylogenetic studies of the flowering plants (1-3). The order contains ∼16,000 species and 42 families (2, 3) that exhibit remarkable morphological and ecological diversity. A few examples include cactus-like succulents (Euphorbiaceae), epiphytes (Clusiaceae), holoparasites (Rafflesiaceae), submerged aquatics (Podostemaceae), and windpollinated trees (temperate Salicaceae). The order is ecologically important: species in Malpighiales constitute up to 40% of the understory tree diversity in tropical rain forests worldwide (4). They also include many economically important species, such as Barbados nut (Jatropha curcas L., Euphorbiaceae), cassava (Manihot esculenta Crantz, Euphorbiaceae), castor bean (Ricinus communis L., Euphorbiaceae), coca (Erythroxylum coca Lam., Erythroxylaceae), flax (Linum usitatissimum L., Linaceae), the poplars (Populus spp., Salicaceae), and the rubber tree (Hevea brasiliensis Müll. Arg., Euphorbiaceae). Partially for this reason, genomic resources for Malpighiales are growing at a rapid pace and include whole-genome sequencing projects completed or near completion for Barbados nut (5), cassava, castor bean (6), flax, and poplar (7). Thus, a resolved phylogeny of Malpighiales is critical not only for evol...
The phenolic biopolymer eumelanin is an important skin pigment found throughout the animal kingdom. The enzyme, tyrosinase, initiates melanogenesis in mammals. The biogenesis is assisted by a number of mammalian protein factors including dopachrome tautomerase and 5,6-dihydroxyindole-2-carboxylate oxidase. Invertebrates, such as insects, employ phenoloxidase and dopachrome (decarboxylating) isomerase for melanin biosynthesis. Recently generated molecular biological and biochemical data indicate that tyrosinase and phenoloxidase are distinctly di erent enzymes in spite of possessing both monophenol monooxygenase activity as well as o-diphenoloxidase activity. Similarly, insect dopachrome isomerase also di ers signi®cantly from its mammalian counterpart in several of its properties including the nature of the enzymatic reaction. In addition, there are considerable di erences in the eumelanogenic pathways of these two animal groups that include the utility of substrates, use of dihydroxyindoles and the nature of eumelanin pigment. Thus, the biochemistry and molecular biology of melanogenesis in mammals and insects are signi®-cantly di erent. The advantages of generating di erent eumelanin pigments and intermediates by the insects are discussed.
Animals synthesize melanin pigments for the coloration of their skin and use it for their protection from harmful solar radiation. Insects use melanins even more ingeniously than mammals and employ them for exoskeletal pigmentation, cuticular hardening, wound healing and innate immune responses. In this review, we discuss the biochemistry of melanogenesis process occurring in higher animals and insects. A special attention is given to number of aspects that are not previously brought to light: (1) the molecular mechanism of dopachrome conversion that leads to the production of two different dihydroxyindoles; (2) the role of catecholamine derivatives other than dopa in melanin production in animals; (3) the critical parts played by various biosynthetic enzymes associated with insect melanogenesis; and (4) the presence of a number of important gaps in both melanogenic and sclerotinogenic pathways. Additionally, importance of the melanogenic process in insect physiology especially in the sclerotization of their exoskeleton, wound healing reactions and innate immune responses is highlighted. The comparative biochemistry of melanization with sclerotization is also discussed.
Phenol oxidase (PO) was isolated as a proenzyme (pro-phenol oxidase, pro-PO) from the hemolymph of Manduca sexta larvae and purified to homogeneity. Pro-PO exhibits a Mr of 130,000 on gel filtration and two bands with an apparent Mr of -100,000 on SDS/PAGE, as well as sizeexclusion HPLC. Activation of pro-PO was achieved either by specific proteolysis by a cuticular protease or by the detergent cetylpyridinium chloride at a concentration below the critical micellar concentration. A cDNA clone for M. sexta pro-PO was obtained from a larval hemocyte cDNA library. The clone encodes a polypeptide of -80,000 Da that contains two copper-binding sites and shows high sequence similarity to POs, hemocyanins, and storage proteins of arthropods. The M. sexta pro-PO, together with other arthropod pro-POs, contains a short stretch of amino acids with sequence similarity to the thiol ester region of a-macroglobulins and complement proteins C3 and C4.Melanin biosynthesis occurs widely, not only in animals but also in plants and fungi (1). Phenol oxidase (PO), which possesses both tyrosinase activity (monophenol monooxygenase; monophenol, L-dopa:oxygen oxidoreductase; EC 1.14.18.1), as well as o-diphenol oxidase (1,2-benzenediol:oxygen oxidoreductase; EC 1.10.3.1), is responsible for initiating the biosynthesis of melanin (2, 3). In arthropods and especially in insects, PO is uniquely involved in another important biochemical process-cuticular sclerotization (hardening). Sclerotization is vital for the survival of all insects, as it affords protection to the soft invertebrate body (3-8). During sclerotization, PO-generated quinones participate in the quinone tanning process or serve as substrates for quinone isomerases that convert quinones to quinone methides for quinone methide sclerotization (9-13). Certain quinone methides are converted by another cuticular enzyme, quinone methide isomerase, to 1,2-dehydro-N-acyldopamine derivatives (14). These compounds are further oxidized by PO to reactive quinone methide imine amides (15, 16), which serve as the reactive intermediates of a,f3-sclerotization. Quinones, quinone methides, and quinone methide imine amides react with cuticular proteins and chitin, forming eventually cross-linked cuticle.Apart from participating in sclerotization and melanization of cuticle, POs are also known to be involved in two other physiologically important processes-defense reactions (arthropod immunity) and wound healing. During invasion by a foreign organism, pro-phenol oxidase (pro-PO) present in the hemocytes is released and activated to produce melanin pigments for deposition on the intruder (17)(18)(19). The damage that can be caused by the foreign organisms is thus limited by encapsulation and melanization. Similarly during wounding of insect cuticle, PO causes massive deposition of melanin pigment at the wound site to prevent hemolymph loss and to block the entry of opportunistically invading microorganisms (20).Given such important functions, it could be expected that PO would be one o...
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