6-Phosphogluconate dehydrogenase 2 bridges the OPP and shikimate pathways to enhance aromatic amino acid production in plants

The oxidative pentose phosphate(OPP)pathway provides metabolic intermediates for the shikimate pathway and directs carbon flow to the biosynthesis of aromatic amino acids(AAAs),which serve as basic protein building blocks and precursors of numerous metabolites essential for plant growth.However,genetic evidence linking the two pathways is largely unclear.In this study,we identified 6-phosphogluconate dehydrogenase 2(PGD2),the rate-limiting enzyme of the cytosolic OPP pathway,through suppressor screening of arogenate dehydrogenase 2(adh2)in Arabidopsis.Our data indicated that a single amino acid substitution at position 63(glutamic acid to lysine)of PGD2 enhanced its enzyme activity by facilitating the dissociation of products from the active site of PGD2,thus increasing the accumulation of AAAs and partially restoring the defective phenotype of adh2.Phylogenetic analysis indicated that the point mutation occurred in a well-conserved amino acid residue.Plants with different amino acids at this conserved site of PGDs confer diverse catalytic activities,thus exhibiting distinct AAAs producing capability.These findings uncover the genetic link between the OPP pathway and AAAs biosynthesis through PGD2.The gain-of-function point mutation of PGD2 identified here could be considered as a potential engineering target to alter the metabolic flux for the production of AAAs and downstream compounds.

Overexpression of the Wounding-Responsive Gene AtMYB15 Activates the Shikimate Pathway in Arabidopsis

The MYB transcription factor genes play important roles in many developmental processes and various defense responses of plants. The shikimate pathway is a major biosynthetic pathway for the production of three aromatic amino acids and other aromatic compounds that are involved in multiple responses of plants, including protection against UV and defense. Herein, we describe the characterization of the R2R3-MYB gene AtMYB15as an activator of the shikimate pathway in Arabidopsis. The AtMYB15 protein is nuclear localized and a transcriptional activation domain is found in its C-terminal portion. Northern blots showed that AtMYB15 is an early wounding-inducible gene. Resutls of microarray analysis, confirmed using quantitative real-time polymerase chain reaction, showed that overexpression of AtMYB15 in transgenic plants resulted in elevated expression of almost all the genes involved in the shikimate pathway. Bioinformatics analysis showed that one or more AtMYB15-binding AC elements were detected in the promoters of these upregulated genes. Furthermore, these genes in the shikimate pathway were also found to be induced by wounding. These data suggest an important role of AtMYB15as a possible direct regulator of the Arabidopsis shikimate pathway in response to wounding.

The shikimate pathway regulates programmed cell death

Programmed cell death(PCD)is essential for both plant development and stress responses including immunity.However,how plants control PCD is not well-understood.The shikimate pathway is one of the most important metabolic pathways in plants,but its relationship to PCD is unknown.Here,we show that the shikimate pathway promotes PCD in Arabidopsis.We identify a photoperiod-dependent lesion-mimic mutant named Lesion in short-day(lis),which forms spontaneous lesions in short-day conditions.Mapbased cloning and whole-genome resequencing reveal that LIS encodes MEE32,a bifunctional enzyme in the shikimate pathway.Metabolic analysis shows that the level of shikimate is dramatically increased in lis.Through genetic screenings,three suppressors of lis(slis)are identified and the causal genes are cloned.SLISes encode proteins upstream of MEE32 in the shikimate pathway.Furthermore,exogenous shikimate treatment causes PCD.Our study uncovers a link between the shikimate pathway and PCD,and suggests that the accumulation of shikimate is an alternative explanation for the action of glyphosate,the most successful herbicide.

Facile Syntheses of (6S)-6-Fluoroshikimic Acid and (6R)-6-Hydroxyshikimic Acid

(6S)-6-Fluoroshikimic acid 2 and (6 R ) 6 hydroxyshikimic acid 3 have been synthesized via an OsO 4 catalysed dihydroxylation of diene 7, which was derived from (-) shikimic acid 1.