Frontier studies on highly selective bio-regulators useful for environmentally benign agricultural production

Abstract

Fungal metabolites active for insects were obtained from fermentation products using okara media. The mechanisms of action of these compounds against insects were clarified using voltage clamp electrophysiology. The branching factor inducing hyphal branching in arbuscular mycorrhizal (AM) fungi was isolated from the root exudates of Lotus japonicus and identified as 5-deoxystrigol. Strigolactones were originally identified as seed germination stimulants of parasitic weeds; therefore, synthetic strigolactones were developed to exhibit the inducing activity of hyphal branching in AM fungi and diminish the stimulating activity of seed germination of parasitic weeds. Signaling molecules, acylhomoserine lactones (AHLs), in quorum sensing were identified in the fungal strain Mortierella alpina A-178, and the true producer of AHLs was clarified as symbiotic bacteria in the fungus. Since acyl-(S)-adenosylmethionine analogs may be good candidates for competitive inhibitors of AHL synthases, intermediate mimics in the biosynthesis of AHLs have been synthesized.

Okaramine insecticidal alkaloids show similar activity on both exon 3c and exon 3b variants of glutamate-gated chloride channels of the larval silkworm, Bombyx mori

“…The first two compounds, okaramines A and B, were isolated as insecticidal compounds from the okara medium fermented by P. simplicissimum and tested by oral application to larvae of the silkworm Bombyx mori (Hayashi et al, 1989). Thereafter, a quest for other okaramines from these fungal metabolites led to the discovery of 16 more compounds (Hayashi, 2015). Of all the okaramine family, okaramine B was the most potent in insect toxicity tests and its potent action was shown to be dependent on the presence of azocine and azetidine rings (Hayashi, 2015, Shiono et al, 2000a.…”

“…Thereafter, a quest for other okaramines from these fungal metabolites led to the discovery of 16 more compounds (Hayashi, 2015). Of all the okaramine family, okaramine B was the most potent in insect toxicity tests and its potent action was shown to be dependent on the presence of azocine and azetidine rings (Hayashi, 2015, Shiono et al, 2000a.…”

An L319F mutation in transmembrane region 3 (TM3) selectively reduces sensitivity to okaramine B of the Bombyx mori l-glutamate-gated chloride channel

“…4) Further exploration of insect-active fungal metabolites led to the isolation of insecticidal meroterpenoids, cyclic peptides as well as the other alkaloids. 5) Although successive discoveries of insect-modulating fungal metabolites were reported, their sites of action remained elusive, triggering investigations on possible targets. When tested on silkworm larvae, uncoordinated motility was rapidly observed, followed by paralysis or death, indicating that such compounds may modulate neural transmission.…”

“…When tested on silkworm larvae, uncoordinated motility was rapidly observed, followed by paralysis or death, indicating that such compounds may modulate neural transmission. 5) Whole-cell patch-clamp electrophysiology was employed to show that whereas asperparaline A 6) and chrodrimanins 7) blocked the acetylcholine-and γ-aminobutyric acid (GABA)induced currents, respectively, okaramines induced chloride currents in neurons. 8) In particular, okaramines activated B. mori L-glutamate-gated chloride channels (BmGluCls), while having no effect on B. mori GABA-gated chloride channels (BmGABACls).…”

The ability of plants to produce strigolactones affects rhizosphere community composition of fungi but not bacteria

“…Two members of the genus Penicillum were more prevalent in the rhizosphere of the wild type compared to max4 plants and bulk soil. A range of bioactive compounds with insecticidal properties have been isolated from Penicillum strains, including okaramines, communesins, chrodrimanins (Hayashi, 2015). It is possible that strigolactones may be involved in plant defence by attracting microbes that play an antagonistic role against pests.…”