In its search for a host, the parasitic plant Striga asiatica must identify a valid target and then trigger its own development to form the parasitic structures, beginning with the attachment organ known as the haustorium. Quinones function as part of the signal transduction cascade that identifies a qualified host in the vicinity.
O'Malley and Lynn have pinpointed expansin gene transcription as a critical component of the mechanism by which the plant perceives that it has received enough signal to commit itself irreversibly. The expansin proteins that are ultimately expressed, given sufficient quinone signal, are responsible for perturbing the biochemistry of the cellulose fibers in the cell wall (as reviewed by Cosgrove) and thus changing its shape as the invading haustorium forms. Expansin messenger RNA accumulates in the presence of quinone signals until a threshold is reached; in a process akin to charging a capacitor, signal can be added discontinuously, although lengthy pauses will cause the accumulated signal to dissipate. — PJH
Plant Cell12, 1455 (2000); Nature407, 321 (2000).
