MLO is a protein unique to plants but with striking similarities to the G-protein-coupled receptor family. Mutations in mlo in barley have been successful in agriculture for the control of powdery mildew fungus (Blumeria graminis f. sp. hordei) but the molecular mechanisms involved remain poorly understood. In March 28 Nature, Min Kim and colleagues from Max-Planck-Institut Köln, Germany, show that calmodulin interacts with MLO to control the defense mechanism against mildew in barley.

Kim et al. used a genetic approach to test for the possible involvement of heterotrimeric G proteins in MLO-dependent defense modulation. They found that MLO functions independently of heterotrimeric G proteins and possesses a domain that mediates a Ca²⁺-dependent interaction with calmodulin in vitro. Loss of calmodulin binding halves the ability of MLO to negatively regulate defense against powdery mildew in vivo (Nature 2002, 416:450).

These results are...