Okaramines and other plant fungal products as new insecticide leads

Okaramine were indole alkaloids discovered from products of Penicillium simplicissimum AK-40 in soy bean pulp 'okara'. Okaramines exhibit insecticidal activity on a broad range of insects. Hence, more insecticide leads were explored by fermenting the other fungi with okara, resulting in the isolations of meroterpenes and cyclic peptides as well as indole alkaloids with distinct skeletons. Most okaramines activate l-glutamate-gated chloride channels found only in invertebrate nervous systems and muscle cells. Other fungal products selectively modulate other invertebrate ligand-gated chloride channels. Recently, the okaramine biosynthetic pathway has been elucidated, providing new insights in structural features important for activity. Enhanced production of okaramine in okara points to the involvement of plant mediators in the production of insect modulators by plant associated microorganisms in the rhizosphere as a novel defense strategy.