The phylogenetic distribution of sterols in tracheophytes

Nes, William R.; Krevitz, Kenneth; Joseph, John; Harris, Barry E.; Gibbons, Geoffrey F.; Patterson, Glenn W.

doi:10.1007/bf02535451

Cited by 121 publications

(40 citation statements)

References 37 publications

(43 reference statements)

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“…This is in complete contrast to what is typically observed in vegetative tissues (Nes and McKean, 1977; Nes et al, 1977; Salt et al, 1991). But given that cholesterol is only a miniscule percentage of a typical vegetative tissue sterol profile (Nes et al, 1977; Salt et al, 1991; Behmer et al, 2011), why is it the dominant sterol within the phloem stream? If cholesterol in the phloem is not acting as a signaling molecule, or providing direct physiological function, perhaps it is present as a precursor to important plant steroid hormones, such as brassinosteroid.…”

Section: Discussioncontrasting

confidence: 78%

“…More than 100 different sterols have been identified from plant vegetative tissue, and individual plants often contain multiple sterols (Nes and McKean, 1977). It is notable, though, that plant sterol composition varies in a predictable manner with phylogeny, such that the sterol profile in plants of one family tend to be more similar to each other than to plants of different, and more distantly related families (Nes et al, 1977; Salt et al, 1991). …”

Section: Introductionmentioning

confidence: 99%

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Plant phloem sterol content: forms, putative functions, and implications for phloem-feeding insects

Behmer¹,

Olszewski²,

Sebastiani³

et al. 2013

Front. Plant Sci.

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All eukaryotes contain sterols, which serve as structural components in cell membranes, and as precursors for important hormones. Plant vegetative tissues are known to contain mixtures of sterols, but very little is known about the sterol composition of phloem. Plants are food for many animals, but plant-feeding arthropods (including phloem-feeding insets) are unique among animals in that they have lost the ability to synthesize sterols, and must therefore acquire these essential nutrients from their food, or via endosymbionts. Our paper starts by providing a very brief overview of variation in plant sterol content, and how different sterols can affect insect herbivores, including those specializing on phloem. We then describe an experiment, where we bulk collected phloem sap exudate from bean and tobacco, and analyzed its sterol content. This approach revealed two significant observations concerning phloem sterols. First, the phloem exudate from each plant was found to contain sterols in three different fractions – free sterols, sterols conjugated to lipids (acylated), and sterols conjugated to carbohydrates (glycosylated). Second, for both plants, cholesterol was identified as the dominant sterol in each phloem exudate fraction; the remaining sterols in each fraction were a mixture of common phytosterols. We discuss our phloem exudate sterol profiles in a plant physiology/biochemistry context, and how it relates to the nutritional physiology/ecology of phloem-feeding insects. We close by proposing important next steps that will advance our knowledge concerning plant phloem sterol biology, and how phloem-sterol content might affect phloem-feeding insects.

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Section: Discussioncontrasting

confidence: 78%

Section: Introductionmentioning

confidence: 99%

Plant phloem sterol content: forms, putative functions, and implications for phloem-feeding insects

Behmer¹,

Olszewski²,

Sebastiani³

et al. 2013

Front. Plant Sci.

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“…In addition, the stereochemistry of the structure of the functional sterols at the end of the pathway, particularly the chirality of the C-24 alkyl group in the sterol side chain, has relative phylogenetic significance. The ,B configuration is found in most primitive organisms (algae and fungi), while a-oriented moieties occur primarily in the more advanced vascular plants (19)(20)(21). In this study, we demonstrate that Prototheca wickerhamii (I) and Dictyostelium discoideum (II) synthesize cycloartenol and 24f3-alkyl sterols, which indicates that they are primitive and derived from photosynthetic organisms, presumably algae, by loss of the chloroplast (see Fig.…”

mentioning

confidence: 50%

Sterol phylogenesis and algal evolution.

Nes¹,

Norton²,

Crumley³

et al. 1990

Proc. Natl. Acad. Sci. U.S.A.

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The stereochemistry of several sterol precursors and end products synthesized by two fungal-like microorganisms Prototheca wickerhamii (I) and Dictyostelium discoideum (H) have been determined by chromatographic (TLC, GLC, and HPLC) and spectral (UV, MS,-and 'H NMR) methods. From I and H the following sterols were isolated from the cells : cycloartenol, cyclolaudenol, 24(28)-methylenecycloartanol, ergosterol, protothecasterol, 4a-methylergostanol, 4a-methylclionastanol, clionastanol, 2413-ethylcholesta-8,22-enol, and dictyosterol. In addition, the mechanism of C-24 methylation was investigated in both organisms by feeding to I[2-3H]lanosterol, [2-3H] Based on what is known in the literature regarding sterol distribution and phylogenesis together with our rmdings that the stereochemical outcome of squalene oxide cyclization leads to the production of cycloartenol rather than lanosterol (characteristic of the fungal genealogy) and the chirality of the C-24 alkyl group is similar in the two nonphotosynthetic microbes (Ji oriented), we conclude that Prototheca is an apoplastic Chlorelia (i.e., an alga) and that Dictyostelium as well as the other soil amoebae that synthesize cycloartenol evolved from algal rather than fungal ancestors.The sterol pathway is thought to be very ancient, perhaps having arisen during the later stages of prokaryote evolution (1, 2). True sterols-e.g., end products such as cholesterolare antedated by the production of sterol-like compoundse.g., pentacyclic triterpenoids (3-6)-which were formed in the Precambrian anaerobic environment by the cyclization of squalene. Once molecular oxygen was in sufficient quantity in the atmosphere to permit squalene oxide genesis, a switching mechanism became operative to divert squalene from pentacyclic triterpenoid production to sterol synthesis (6, 7). The first compounds derived by the anaerobic cyclization of squalene oxide are the tetracyclic stereoisomers cycloartenol and lanosterol. Neither stereoisomer is known to be formed by cyclization in the same organism, whether the latter is a prokaryote or a eukaryote (2). This bifurcation in the sterol pathway is now recognized in biochemical textbooks (8-10) and in reviews on evolution (11-13) as a means to dissociate groups of organisms with an evolutionary history of oxygenic photosynthesis-e.g., as detected through the stereospecific formation of cycloartenol and its further metabolism of the 96,19-cyclopropyl ring-from those nonphotosynthetic progenitors and their descendants, which possess a lanosterolbased pathway (2). The association of the cycloartenol route and the endosymbiotic origin and subsequent loss of the chloroplast in some nonphotosynthetic systems is not clear. The biosynthesis of cycloartenol occurs in microsomes (14) and proceeds when the chloroplast is absent (15-18). In neither case is the biosynthesis of the stereoisomer influenced by the structure of the functional steroid at the end of the pathway, and their occurrence is not influenced by the molecular clock or mutatio...

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“…When the individual sterols, from these mixtures of sterols, were separated using preparative RPLC, not only did GLC analysis of the individual peaks confirm the above identifications but the M+ and fragmentation pattern of each sterol in MS was consistent with the presence of cholesterol (M+ = mle 386, 100%; M+-85 = 301, 75%; dehydrocholesterol (M+ = 384, 100%; Mf-CH3 = 369,l8%; M+-H20-CH3 = = 227, 44%), and ergosterol (M+ = 396) [8]. The presence of these three sterols was confirmed by 'H-NMR.…”

Section: Utilization Of Ergosterolmentioning

confidence: 85%

Utilization of Δ^5,7 ‐ and Δ⁸‐sterols by larvae of Heliothis zea

Ritter

1986

Arch Insect Biochem Physiol

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Larvae from two populations of Heliothis zea were reared on artificial diets containing various sterols, which supported suboptimal growth, and their tissue sterols were characterized in order to determine how these dietary sterols are utilized by this insect. The sterols studied included A5r7-sterols (7-dehydrocholesterol or ergosterol), A8-sterols (lanosterol andlor 2Cdihydro-lanosterol), and a A5-sterol (4,4-dimethylcholesterol). Although larvae did not develop on 4,4dimethylcholesterol, those fed primarily A8-4,4,14trimethyl-sterols developed to the third instar. When the latter sterols were spared with cholesterol, the larvae reached the sixth instar and contained 4,4,14-trimethylsterols as well as cholesterol in their tissues. When larvae were fed 7-dehydrocholesterol, < 1 % of the larvae from one population developed to the sixth instar and these larvae contained 7-dehydrocholesterol as their principal sterol. The other larvae successfully completed their larval stage when they were transferred from the diet containing 7-dehydrocholesterol (or no sterol) to a diet containing cholesterol within at least 9 days. The sterol composition of larvae transferred from a diet containing cholesterol to a diet containing 7-dehydrocholesterol, after they had reached 60% of their final weight, was 54% cholesterol and 46% 7-dehydrocholesterol. The major sterol isolated from the tissues of the larvae fed ergosterol was also 7-dehydrocholesterol. Therefore, although the larva of H. zea can dealkylate and saturate the side chain of the A5,7,22-24fhnethylsteroI, it carries out little metabolism of the B ring of the nucleus. These studies demonstrate that, when A5r7-or A8-sterols are the principal sterols in the diet of H. zea, they are absorbed and incorporated into i t s tissues, although they slow the rate of growth and may prevent complete development of the larva.

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The phylogenetic distribution of sterols in tracheophytes

Cited by 121 publications

References 37 publications

Plant phloem sterol content: forms, putative functions, and implications for phloem-feeding insects

Plant phloem sterol content: forms, putative functions, and implications for phloem-feeding insects

Sterol phylogenesis and algal evolution.

Utilization of Δ^5,7 ‐ and Δ⁸‐sterols by larvae of Heliothis zea

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The phylogenetic distribution of sterols in tracheophytes

Cited by 121 publications

References 37 publications

Plant phloem sterol content: forms, putative functions, and implications for phloem-feeding insects

Plant phloem sterol content: forms, putative functions, and implications for phloem-feeding insects

Sterol phylogenesis and algal evolution.

Utilization of Δ5,7 ‐ and Δ8‐sterols by larvae of Heliothis zea

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Utilization of Δ^5,7 ‐ and Δ⁸‐sterols by larvae of Heliothis zea