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.

Gender Specific Variation of Two Phenolic Glycosides (Populin and Salicin) in Populus Ciliata and Identification of a New Compound (Cinnamoyl-Salicin)

“…Such type of variation was previously reported among plants in the total level of PG's [2,7]. The comparison of salicin and populin content revealed that the concentration of salicin and populin content is higher in males than in females, which could be the reason of lower susceptibility of male towards floral pathogens.…”

“…But the content and type of the PG's are found to be different among Populus species [6][7][8]. The variation in the amount of PG's can be accounted to environmental conditions, plant gender or clonal differences and influences the plant susceptibility to insects [9][10][11][12].…”

Alternative splicing and gene duplication differentially shaped the regulation of isochorismate synthase in Populus and Arabidopsis

“…Because ICS regulates the utilization of chorismate for both photosynthesis and defense, ICS may control cross-talk between primary and secondary metabolism. Coordination of such cross-talk differs between Arabidopsis and species such as Populus that constitutively maintain large and highly variable reserves of nonstructural phenylpropanoid metabolites (e.g., PGs and flavonoid-derived condensed tannins) in their leaves, shoots, and roots (14,15). Here, we report alternative splicing and gene duplication as two contrasting mechanisms for modulating higher-plant ICS function.…”

“…Populus plants were grown in soil in pots and maintained in a greenhouse, as described (15). Arabidopsis plants were grown in Metro-Mix 300 (Sun Gro) and maintained in a growth chamber at 22°C under a 16-h photoperiod.…”

Identification of differentially expressed genes involved in spine formation on seeds ofDaucus carota L. (carrot), using annealing control primer (ACP) system

“…Both Sadenosyl methionine synthase (GP57) and berberine bridge enzyme (GP48) are expressed similarly to phenylpropanoid metabolism (Harding et al, 2005). For example, berberine bridge enzyme is induced in cultured opium poppy cells in response to wounding or treatment with a pathogen-derived elicitor (Park et al, 1999), while transcription of SAMS genes is induced in elicited cells of alfalfa (Gowri et al, 1991 ).…”