Sentence:  The monolignol substrates are held in position by proteins called <WSD>dirigents</WSD> (guide proteins)....Lignan dirigent proteins are found in the cytoplasm, but similar <WSD>dirigents</WSD> have been localized in the cell walls of some plants. 
Meaning of the word marked with <WSD> tags:  Something that or someone who directs; a director or guide.