Lignin, one of the most abundant biopolymers on Earth, derives from the plant phenolic metabolism. It appeared upon terrestrialization and is thought critical for plant colonization of land. Early diverging land plants do not form lignin, but already have elements of its biosynthetic machinery. Here we delete in a moss the P450 oxygenase that defines the entry point in angiosperm lignin metabolism, and find that its pre-lignin pathway is essential for development. This pathway does not involve biochemical regulation via shikimate coupling, but instead is coupled with ascorbate catabolism, and controls the synthesis of the moss cuticle, which prevents desiccation and organ fusion. These cuticles share common features with lignin, cutin and suberin, and may represent the extant representative of a common ancestor. Our results demonstrate a critical role for the ancestral phenolic metabolism in moss erect growth and cuticle permeability, consistent with importance in plant adaptation to terrestrial conditions.
Background: Shikimate is essential for protein biosynthesis. Quinate and its derivatives are protective secondary metabolites. Results: Members of the same gene family encode enzymes with either shikimate or quinate dehydrogenase activity. Conclusion:The molecular genetic basis of plant quinate metabolism has been unraveled in vitro. Significance: Identifying quinate metabolic enzymes will allow testing its ecological function and may enable biotechnological applications.
Summary Multiple adaptations were necessary when plants conquered the land. Among them were soluble phenylpropanoids related to plant protection and lignin necessary for upright growth and long‐distance water transport. Cytochrome P450 monooxygenase 98 (CYP98) catalyzes a rate‐limiting step in phenylpropanoid biosynthesis. Phylogenetic reconstructions suggest that a single copy of CYP98 founded each major land plant lineage (bryophytes, lycophytes, monilophytes, gymnosperms and angiosperms), and was maintained as a single copy in all lineages but the angiosperms. In angiosperms, a series of independent gene duplications and losses occurred. Biochemical assays in four angiosperm species tested showed that 4‐coumaroyl‐shikimate, a known intermediate in lignin biosynthesis, was the preferred substrate of one member in each species, while independent duplicates in Populus trichocarpa and Amborella trichopoda each showed broad substrate ranges, accepting numerous 4‐coumaroyl‐esters and ‐amines, and were thus capable of producing a wide range of hydroxycinnamoyl conjugates. The gymnosperm CYP98 from Pinus taeda showed a broad substrate range, but preferred 4‐coumaroyl‐shikimate as its best substrate. In contrast, CYP98s from the lycophyte Selaginella moellendorffii and the fern Pteris vittata converted 4‐coumaroyl‐shikimate poorly in vitro, but were able to use alternative substrates, in particular 4‐coumaroyl‐anthranilate. Thus, caffeoyl‐shikimate appears unlikely to be an intermediate in monolignol biosynthesis in non‐seed vascular plants, including ferns. The best substrate for CYP98A34 from the moss Physcomitrella patens was also 4‐coumaroyl‐anthranilate, while 4‐coumaroyl‐shikimate was converted to lower extents. Despite having in vitro activity with 4‐coumaroyl‐shikimate, CYP98A34 was unable to complement the Arabidopsis thaliana cyp98a3 loss‐of‐function phenotype, suggesting distinct properties also in vivo.
Insights into the physiology of nitrogen (N) uptake help us to understand the adaption of boreal coniferous forests to their environment. We compared fluxes of nitrate and ammonium in white spruce [Picea glauca (Moench) Voss] roots, measured using a noninvasive microelectrode ion flux measurement system (MIFE), and transcript abundance of ammonium and nitrate transporter genes in roots, determined by real time PCR. Seedlings were pretreated with water, or 50 lM or 1,500 lM NH 4 NO 3 ? 200 lM CaSO 4 ? 25 lM KH 2 PO 4 . Measurements were made on seedling roots 0-5, 5-10, 10-20 and 20-30 mm from the root tip. As ammonium and nitrate transporter family members in spruce are still uncharacterized, primers for real time PCR were designed to cover one family with each set of primers (AMT1, AMT2, NRT1, NRT2). The expression patterns obtained by real time PCR differed significantly among transporter family, treatments and root segments. Expression of AMT1 did not show a relationship with distance from the root tip, but the expression of AMT2 was generally greater 0-5 mm from the root tip than in segments farther from the tip. Expression of NRT1 was greatest 10-30 mm from the root tip, while expression of NRT2 was greatest 5-10 mm from the tip in all treatments, except the 1,500 lM NH 4 NO 3 treatment. MIFE measurements showed the highest N uptake and proton efflux near the root tip and declining fluxes with increased distance from the root tip in the 50 lM N treatment. Significant net ammonium efflux was observed from some root segments in the 1,500 lM N treatment. Transporter gene expression and ion fluxes were not correlated. Though the measured net fluxes of ammonium were greater than the measured net fluxes of nitrate, the nitrate transporters were, in general, more highly expressed than the ammonium transporters.Keywords AMT1 Á AMT2 Á NRT1-NRT2 Á Nitrogen uptake Á Ammonium transporter Á Nitrate transporter Á Ammonium flux Á Nitrate flux Á Root regions Á Ion flux profile
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