title: Functional genomics analysis of foliar condensed tannin and phenolic glycoside regulation in natural cottonwood hybrids.
abstract: Regulation of leaf condensed tannins (CT) and salicylate-derived phenolic glycosides (PG) in fast- and slow-growing cottonwood backcrosses was analyzed by metabolic profiling and cDNA microarray hybridization. Seven hybrid lines of Populus fremontii L. and P. angustifolia James exhibiting growth/CT-PG phenotypes ranging from fast/low (Lines 18 and 1979) to slow/high (Lines 1012 and RL2) and intermediate (Lines NUL, 3200 and RM5) were investigated. Methanol-extractable leaf metabolites were analyzed by gas chromatography-mass spectrometry, and the results evaluated by principal component analysis. The hybrid lines formed separate clusters based on their primary metabolite profiles, with cluster arrangement also reflecting differences in CT-PG phenotype. Nitrogen (N) supply was manipulated to alter CT-PG partitioning and to obtain molecular insights into how primary metabolism interfaces with CT-PG accumulation. Three backcross lines (RM5, 1012, 18) exhibiting differential CT-PG responses to a 10-day hydroponic N-deprivation treatment were chosen for metabolite and gene expression analyses. The fast- growing Line 18 showed a minimal CT-PG response to N deprivation, and a reduction in photosynthetic gene expression. Line 1012 exhibited a strong phenylpropanoid response to N deprivation, including a doubling in phenylalanine ammonia-lyase (PAL) gene expression, and a shift from CT accumulation in the absence of stress toward PG accumulation under N-deprivation conditions. Amino acid concentrations were depressed in Lines 18 and 1012, as was expression of nitrate-sensitive genes coding for transketolase (TK), and malate dehydrogenase (MDH). Genes associated with protein synthesis and fate were down-regulated in Line 1012 but not in Line 18. Line RM5 exhibited a comparatively large increase in CT in response to N deprivation, but did not sustain decreases in amino acid concentrations, or changes in PAL, TK or MDH gene expression. Molecular characterization of the variable CT-PG responses shows promise for the identification and future testing of candidate genes for CT-PG trait selection or manipulation.
authors.affiliation: Biotechnology Research Center, School of Forest Resources and Environmental Science, Michigan Technological University, Houghton, MI 49931, USA.
authors.forename: Scott A
authors.initials: SA
authors.lastname: Harding
authors.forename: Hongying
authors.initials: H
authors.lastname: Jiang
authors.forename: Mijeong Lee
authors.initials: ML
authors.lastname: Jeong
authors.forename: Fanny L
authors.initials: FL
authors.lastname: Casado
authors.forename: Han-Wei
authors.initials: HW
authors.lastname: Lin
authors.forename: Chung-Jui
authors.initials: CJ
authors.lastname: Tsai
mesh_terms: D008401:Gas Chromatography-Mass Spectrometry; D020869:Gene Expression Profiling; D018506:Gene Expression Regulation, Plant; D018745:Genome, Plant; D023281:Genomics; D006027:Glycosides / Q000378:metabolism*; D006824:Hybridization, Genetic; D009584:Nitrogen / Q000378:metabolism; D010636:Phenols / Q000378:metabolism*; D018515:Plant Leaves / Q000378:metabolism*; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D032107:Populus / Q000235:genetics* / Q000378:metabolism*; D044945:Proanthocyanidins / Q000378:metabolism*
chemical_list: D006027:Glycosides; D010636:Phenols; D010940:Plant Proteins; D044945:Proanthocyanidins; D009584:Nitrogen