Kozo Nagayama

Acetolactate Synthase Inhibitors

Acetolactate synthase (ALS; EC 4.6.3.8, also referred to acetohydroxy acid synthase; AHAS) is the first common enzyme in the biosynthetic pathway to the branched-chain amino acids; valine, leucine and isoleucine (Fig. 1). The pathway exists in plants and microorganisms such as bacteria, fungi and algae. ALS is the primary target site of action for at least four structurally distinct classes of herbicides including the sulfonylureas (SUs; LaRossa and Schloss 1984; Ray 1984), the imidazolinones (IMs; Shaner et al. 1984), the triazolopyrimidine sulfonamides (TPs; Subramanian and Gerwick 1989) and the pyrimidinylsalicylates (pyrimidinyl carboxy herbicides, PCs; Shimizu et al. 1994b), all of which have been successful in their development as commercial herbicides. The extremely good weed control activity achieved with these herbicides indicates that ALS is a very effective target site for herbicidal action. Deficiency of the pathway of branched-chain amino acids biosynthesis in mammals (Singh and Shaner 1995) shows us that it is the selective target between plants and mammals. ALS is therefore attractive for addressing a large number of goals of modern herbicide research.

Identification of Trichoderma SKT-1, a biological control agent against seedborne pathogens of rice

Trichoderma SKT-1 was previously reported as a powerful biological control agent against seedborne pathogens of rice, but the taxonomic disposition of the fungal isolate was not clear. Trichoderma SKT-1 produced irregular pyramidal warts on conidia and had an optimum growth temperature of 30°C. Morphological characteristics and colony growth were identical to those of known species of Trichoderma, including the newly recognized species T. asperellum. The 5.8S rDNA with the internal transcribed spacer (ITS) region (ca. 514 bp) of the fungus was compared with those of known species to determine the phylogenetic placement of the fungus. The length and sequence of the regions from Trichoderma SKT-1 were completely identical to those of an isolate of T. asperellum NRRL 5242 (AJ230669). On the basis of these results, we concluded that Trichoderma SKT-1 was T. asperellum.