A herbicide with a new mode of actions (MOAs) has not been introduced for about 30 years. During this time, resistance has evolved at steady pace to the herbicides with the ca. 25 old MOAs, creating a strong need for herbicides with new MOAs. Spliceostatin C, a compound from the soil microbe Burkholderia rinojensis, is a very effective herbicide at low doses with several important weed species such as Amaranthus spp. A related compound spliceostatin A, also from a Burkholderia species acts as a spliceosome inhibitor. Herboxidiene, produced by Streptomyces chromofuscus, is a selective herbicide, and recent studies have shown it to also disrupt the mRNA splicing process in animal cells. In this report, Arabidopsis was used to investigate the phytotoxic properties and possible modes of action of spliceostatin C and herboxidiene in plant cells. Both spliceostatin C and herboxidiene caused leaf bleaching and significantly inhibited leaf and root growth. Dose-response assays showed that the half maximal inhibitory concentration (IC50) of spliceostatin C and herboxidiene were 2.2 and 0.37 µM, respectively. At IC80, spliceostatin C (15.2 µM) and herboxidiene (1.72 µM) disrupted gravitropism and inhibited lateral branching in roots. To study the inhibition of spliceosomal catalysis, twenty genes including intronless genes, regulation factors, genes encoding multiple transcripts, and stably expressed genes were selected for gene expression analyses using semi-quantitative reverse transcription-polymerase chain reaction. Seven-day old Arabidopsis seedlings were exposed to spliceostatin C or herboxidiene at the IC50 and IC80 concentrations. Spliceostatin C and herboxidiene generated slightly different gene expression patterns. The expression of most of these genes after exposure to these compounds was significantly changed. However, in several cases, the transcripts affected by both inhibitors, exhibited additional and longer transcripts, either by alternative intron splicing or by alternative 5’ or 3’ splicing. Although the number of transcripts stayed the same, their level of expression as affected by herboxidiene differed from those affected by spliceostatin C. Further study is needed to determine factors responsible for the differences. The results strongly support the view that spliceostatin C has a new MOA, spliceosome inhibition.

Mode of action of spliceostatin C, a potent herbicidal compound from a microbe

256th National Meeting (2018)

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