Structure and function of enzymes involved in the biosynthesis of phenylpropanoids

Establishment of a protein reference map for soybean root hair cells

Root hairs are single tubular cells formed from the differentiation of epidermal cells on roots. They are involved in water and nutrient uptake and represent the infection site on leguminous roots by rhizobia, soil bacteria that establish a nitrogen-fixing symbiosis. Root hairs develop by polar cell expansion or tip growth, a unique mode of plant growth shared only with pollen tubes. A more complete characterization of root hair cell biology will lead to a better understanding of tip growth, the rhizobial infection process, and also lead to improvements in plant water and nutrient uptake. We analyzed the proteome of isolated soybean (Glycine max) root hair cells using two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) and shotgun proteomics (1D-PAGE-liquid chromatography and multidimensional protein identification technology) approaches. Soybean was selected for this study due to its agronomic importance and its root size. The resulting soybean root hair proteome reference map identified 1,492 different proteins. 2D-PAGE followed by mass spectrometry identified 527 proteins from total cell contents. A complementary shotgun analysis identified 1,134 total proteins, including 443 proteins that were specific to the microsomal fraction. Only 169 proteins were identified by the 2D-PAGE and shotgun methods, which highlights the advantage of using both methods. The proteins identified are involved not only in basic cell metabolism but also in functions more specific to the single root hair cell, including water and nutrient uptake, vesicle trafficking, and hormone and secondary metabolism. The data presented provide useful insight into the metabolic activities of a single, differentiated plant cell type.

Chapter 9. Synthetic probes for polyketide and nonribosomal peptide biosynthetic enzymes

Polyketides and nonribosomal peptides constitute two classes of small molecule natural products that are well-known for their ability to impact important biological processes in a multitude of ways. The modular biosynthetic enzymes responsible for production of these compounds (PKS and NRPS enzymes) have been the subject of extensive genetic, biochemical, and structural characterization, in part due to the potential utility their successful reengineering may have for the production of new therapeutics. In this chapter, we provide background as well as specific techniques in which synthetically produced small molecule probes have been applied to help better understand the mechanism and structure of PKS and NRPS biosynthetic pathways, as well as to help streamline their discovery process. The continued development and application of these methods has the potential to greatly complement our current approaches to the study of natural product biosynthesis.

Genetic background impacts soluble and cell wall-bound aromatics in brown midrib mutants of sorghum

Sorghum (Sorghum bicolor (L.). Moench) BMR-6 and BMR-12 encode cinnamylalcohol dehydrogenase and caffeic acid-O-methyltransferase, respectively. We have evaluated the impact of two bmr alleles, bmr-6 and bmr-12, respectively, on soluble and wall-bound aromatics in near isogenic, wild-type (WT), bmr-6, bmr-12 and double-mutant (DM; bmr-6 and bmr-12) plants in two genetic backgrounds, RTx430 and Wheatland. Immunoblots confirmed that COMT protein was essentially absent in bmr-12 and DM plants, but was present in bmr-6 and WT plants. In contrast, although CAD activity was not detected in bmr-6 and DM plants, proteins crossreacting to anti-CAD sera were found in stem extracts from all genotypes. In both sorghum backgrounds, WT plants had lowest amounts of free aromatics, higher levels of cell wall-bound pCA and FA esters and guaiacyl (G), syringyl (S), and p-hydroxyphenyl (H) lignins. Soluble aromatics and cell wall phenolic ester content in Wheatland DM plants resembled that of Wheatland bmr-6 plants, whereas in the RTx430 background, levels of these components in the DM plants more closely resembled those observed in bmr-12 plants. In both backgrounds, bmr-6 plants exhibited reduced levels of G, S, and H lignins relative to WT, and increased incorporation of G-indene into lignin. In bmr-12 plants, there was greater incorporation of G- and 5-hydroxyguaiacyl (5-OHG) lignin into cell walls. Histochemical staining of internode sections from Wheatland plants indicated that apparent lignification of cortical sclerenchyma and vascular bundle fibers was greatest and most uniform in WT plants. Relative staining intensity of these tissues was decreased in bmr-6, followed by bmr-12 plants. DM plants exhibited poor staining of cortical sclerenchyma and vascular bundle fibers.

Metabolic analysis of the cinnamate/monolignol pathway in Carthamus tinctorius seeds by a stable-isotope-dilution method

The present study established a system for comprehensive metabolic analysis of the cinnamate/monolignol and lignan pathways by the use of a stable-isotope-dilution method. The system was successfully applied to characterization of the pathways in Carthamus tinctorius cv. Round-leaved White maturing seeds in combination with administration of stable-isotope-labelled precursors. Experimental results obtained using this technique strongly suggested the intermediacy of ferulic acid in lignan biosynthesis in the plant.