Xanthothricin

The toxoflavin (Txn), broad host range phytotoxin produced by a variety of bacteria, including Burkholderia glumae, is a key pathogenicity factor of B. glumae in rice and field crops. Two bacteria exhibiting Txn-degrading activity were isolated from healthy rice seeds and identified as Sphingomonas adhaesiva and Agrobacterium sp. respectively. The genes stdR and stdA, encoding proteins responsible for Txn degradation of both bacterial isolates, were identical, indicating that horizontal gene transfer occurred between microbial communities in the same ecosystem. We identified a novel Txn-quenching regulation of bacteria, demonstrating that the LysR-type transcriptional regulator (LTTR) StdR induces the expression of the stdA, which encodes a Txn-degrading enzyme, in the presence of Txn as a coinducer. Here we show that the bacterial StdRTxn-quenching regulatory system mimics the ToxRTxn-mediated biosynthetic regulation of B. glumae. Substrate specificity investigations revealed that Txn is the only coinducer of StdR and that StdA has a high degree of specificity for Txn. Rice plants expressing StdA showed Txn resistance. Collectively, bacteria mimic the mechanism of Txn biosynthesis regulation, employ it in the development of a Txn-quenching regulatory system and share it with neighbouring bacteria for survival in rice environments full of Txn.

We investigated the synthesis and herbicidal activity of 23 toxoflavin analogs,1a-w, in which aromatic rings (R) were introduced into the C-3 position. In paddy field conditions,1k(R=2-CF3-C6H4) and1w(R=2-thienyl) showed excellent herbicidal activity. Under upland field conditions, we found that toxoflavin analogs1a(R=C6H5),1n(R=2-CH3O-C6H4), and1p(R=4-CH3O-C6H4) exhibited wide herbicidal spectrum againstEchinochloa crus-galli (L) var. crus-galli(ECHCG),Chenopodium album, andAmaranthus viridis(AMAVI). The analog with the 2-fluoro group on benzene ring1balso showed high herbicidal activity against both ECHCG and AMAVI.

Reaction of xanthothricin demethylation by amines in acetone as a solvent yielded a new compound with a formula of C10H13N5O3. Mass spectrometry, 1H NMR-spectroscopy and x-ray analysis showed that the compound was 4H-1,6-dimethyl-4a(2-oxopropyl)-pyrimido-[5,4-e]-1 ,2,4-triazine-5,7-dione.