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Cadmium interferes with auxin physiology and lignification in poplar.

ABSTRACT: Cadmium (Cd) is a phytotoxic heavy metal that causes rapid growth reduction. To investigate if Cd interferes with the metabolism of auxin, a major growth hormone in plants, poplars (Populus × canescens) expressing a heterologous GH3::GUS reporter gene were exposed to 50 ?M Cd in hydroponic solutions. Growth, photosynthetic performance, lignification, peroxidase activity, auxin concentration, and GUS staining were determined in order to record the activities of GH3 enzymes in the stem apex, the elongation zone, wood in the zone of radial growth, and in roots. Cd-induced growth reductions were tissue-specific decreasing in the order: roots>wood>shoot elongation and leaf initiation, whereas Cd concentrations increased in the order: leaves

SUBMITTER: Elobeid M

PROVIDER: S-EPMC3276104 | biostudies-literature | 2012 Feb

REPOSITORIES: biostudies-literature

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Cadmium interferes with auxin physiology and lignification in poplar.

Elobeid Mudawi M Göbel Cornelia C Feussner Ivo I Polle Andrea A

Journal of experimental botany 20111203 3

Cadmium (Cd) is a phytotoxic heavy metal that causes rapid growth reduction. To investigate if Cd interferes with the metabolism of auxin, a major growth hormone in plants, poplars (Populus × canescens) expressing a heterologous GH3::GUS reporter gene were exposed to 50 μM Cd in hydroponic solutions. Growth, photosynthetic performance, lignification, peroxidase activity, auxin concentration, and GUS staining were determined in order to record the activities of GH3 enzymes in the stem apex, the e ...[more]

PMID: 22140243

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Project description:Lignocellulosic biomass is recalcitrant toward deconstruction into simple sugars mainly due to the presence of lignin. By engineering plants to partially replace traditional lignin monomers with alternative ones, lignin degradability and extractability can be enhanced. Previously, the alternative monomer curcumin has been successfully produced and incorporated into lignified cell walls of Arabidopsis by the heterologous expression of DIKETIDE-CoA SYNTHASE (DCS) and CURCUMIN SYNTHASE2 (CURS2). The resulting transgenic plants did not suffer from yield penalties and had an increased saccharification yield after alkaline pretreatment. Here, we translated this strategy into the bio-energy crop poplar. Via the heterologous expression of DCS and CURS2 under the control of the secondary cell wall CELLULOSE SYNTHASE A8-B promoter (ProCesA8-B), curcumin was also produced and incorporated into the lignified cell walls of poplar. ProCesA8-B:DCS_CURS2 transgenic poplars, however, suffered from shoot-tip necrosis and yield penalties. Compared to that of the wild-type (WT), the wood of transgenic poplars had 21% less cellulose, 28% more matrix polysaccharides, 23% more lignin and a significantly altered lignin composition. More specifically, ProCesA8-B:DCS_CURS2 lignin had a reduced syringyl/guaiacyl unit (S/G) ratio, an increased frequency of p-hydroxyphenyl (H) units, a decreased frequency of p-hydroxybenzoates and a higher fraction of phenylcoumaran units. Without, or with alkaline or hot water pretreatment, the saccharification efficiency of the transgenic lines was equal to that of the WT. These differences in (growth) phenotype illustrate that translational research in crops is essential to assess the value of an engineering strategy for applications. Further fine-tuning of this research strategy (e.g., by using more specific promoters or by translating this strategy to other crops such as maize) might lead to transgenic bio-energy crops with cell walls more amenable to deconstruction without settling in yield.

Project description:Drought is one of the main environmental factors limiting plant growth and development. The AP2/ERF transcription factor (TF) ERF194 play key roles in poplar growth and drought-stress tolerance. However, the physiological mechanism remains to be explored. In this study, the ERF194-overexpression (OX), suppressed-expression (RNA interference, RNAi), and non-transgenic (WT) poplar clone 717 were used to study the physiology role of ERF194 transcription factor in poplar growth and drought tolerance. Morphological and physiological methods were used to systematically analyze the growth status, antioxidant enzyme activity, malondialdehyde (MDA), soluble sugars, starch, and non-structural carbohydrate (NSC) contents of poplar. Results showed that, compared with WT, OX plants had decrease in plant height, internode length, and leaf area and increased number of fine roots under drought stress. In addition, OX had higher water potential, activities of superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD), contents of chlorophyll, soluble sugar, starch, and NSC, implying that ERF194 positively regulates drought tolerance in poplar. The growth status of RNAi was similar to those of WT, but the relative water content and CAT activity of RNAi were lower than those of WT under drought treatment. Based on the transcriptome data, functional annotation and expression pattern analysis of differentially expressed genes were performed and further confirmed by RT-qPCR analysis. Gene ontology (GO) enrichment and gene expression pattern analysis indicated that overexpression of ERF194 upregulated the expression of oxidoreductases and metabolism-related genes such as POD and SOD. Detection of cis-acting elements in the promoters suggested that ERF194 may bind to these genes through MeJA-responsive elements, ABA-responsive elements, or elements involved in defense and stress responses. The above results show that ERF194 improved tolerance to drought stress in poplar by regulating its growth and physiological factors. This study provides a new idea for the role of ERF194 transcription factor in plant growth and drought-stress response.

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Cadmium interferes with auxin physiology and lignification in poplar.

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Cadmium interferes with auxin physiology and lignification in poplar.

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