Both the monolignol and the shikimate-chorismate biochemical pathways have been ex­tensively studied over a period spanning nearly five decades. As regards the former, the reader is highly encouraged to review the two most comprehensive treatises on monolignol biosynthesis (31) and monolignol pathway genetic manipulation (77). The first provides an historical account of the pioneering work in enzyme identification, enzyme isolation, and subsequent gene cloning in the monolignol/lignin pathway, whereas the second largely attempts to identify predictable trends in downregulating/mutating various pathways steps, e. g., following application of standard molecular biological approaches. Interestingly, the five-decade held view that lignins were randomly assembled had apparently all but deterred many researchers in this field from systematically studying — in a productive and predictive hypothesis-driven manner — the effects of manipulating the lignin-forming apparatus.

Moreover, although there are occasional reports describing the monolignol pathway as being recently redrawn in the past few years (78), in hindsight this is really not the case. Instead, a number of discoveries had been made — some up to a quarter of a century ago — whose significance had not yet been appreciated by various researchers at the time. We, therefore, briefly review the monolignol pathway, the highlights of recent years, and the recent advances made in understanding the nature of metabolic pathway flux associated with monolignol/lignin formation. Furthermore, because of the completion of the Ara — bidopsis genome sequencing in 2000 (79), an emphasis is also placed on the study of the phenylpropanoid-forming biochemical machinery in that organism as it is currently the most extensively studied.