Arogenate Dehydratase Isoenzymes Profoundly and Differentially Modulate Carbon Flux into Lignins

• Published in: The Journal of biological chemistry 2012-03, Vol.287 (14), p.11446-11459
• Main Authors: Corea, Oliver R.A., Ki, Chanyoung, Cardenas, Claudia L., Kim, Sung-Jin, Brewer, Sarah E., Patten, Ann M., Davin, Laurence B., Lewis, Norman G.
• Format: Article
• Language: English
• Subjects: Acetates - metabolism; Amino Acid; Arabidopsis; Arabidopsis - cytology; Arabidopsis - enzymology; Arabidopsis - genetics; Arabidopsis - metabolism; Arogenate; Biosynthesis; Carbon - metabolism; Carbon allocation; Chloroplasts - enzymology; Chloroplasts - metabolism; Gene Expression Regulation, Plant; Gene Knockout Techniques; Glucuronidase - genetics; Hydro-Lyases - deficiency; Hydro-Lyases - genetics; Hydro-Lyases - metabolism; Isoenzymes - deficiency; Isoenzymes - genetics; Isoenzymes - metabolism; Lignin; Lignin - metabolism; Metabolism; Phenotype; Plant Cell Wall; Polyphenols; Protein Transport; Thioacidolysis; Vascular Bundles
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M111.322164

How carbon flux differentially occurs in vascular plants following photosynthesis for protein formation, phenylpropanoid metabolism (i.e. lignins), and other metabolic processes is not well understood. Our previous discovery/deduction that a six-membered arogenate dehydratase (ADT1–6) gene family encodes the final step in Phe biosynthesis in Arabidopsis thaliana raised the fascinating question whether individual ADT isoenzymes (or combinations thereof) differentially modulated carbon flux to lignins, proteins, etc. If so, unlike all other lignin pathway manipulations that target cell wall/cytosolic processes, this would be the first example of a plastid (chloroplast)-associated metabolic process influencing cell wall formation. Homozygous T-DNA insertion lines were thus obtained for five of the six ADTs and used to generate double, triple, and quadruple knockouts (KOs) in different combinations. The various mutants so obtained gave phenotypes with profound but distinct reductions in lignin amounts, encompassing a range spanning from near wild type levels to reductions of up to ∼68%. In the various KOs, there were also marked changes in guaiacyl:syringyl ratios ranging from ∼3:1 to 1:1, respectively; these changes were attributed to differential carbon flux into vascular bundles versus that into fiber cells. Laser microscope dissection/pyrolysis GC/MS, histochemical staining/lignin analyses, and pADT::GUS localization indicated that ADT5 preferentially affects carbon flux into the vascular bundles, whereas the adt3456 knock-out additionally greatly reduced carbon flux into fiber cells. This plastid-localized metabolic step can thus profoundly differentially affect carbon flux into lignins in distinct anatomical regions and provides incisive new insight into different factors affecting guaiacyl:syringyl ratios and lignin primary structure. Background: The plastid-localized arogenate dehydratase (ADT) gene family is hypothesized to differentially control carbon flux for lignin deposition, with lignin being the main contributor to lignocellulosic recalcitrance. Results: Single and multiple ADT knock-outs resulted in differential control over lignin content/composition. Conclusion: The first evidence for Phe upstream metabolism differentially controlling carbon flux into distinct secondary cell wall types was discovered. Significance: Upstream metabolic networks regulate secondary cell wall formation.