Submitted to: Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 16, 2003
Publication Date: July 1, 2003
Citation: Keates, S.E., Kostman, T.A., Anderson, J.D., Bailey, B.A. 2003. Altered gene expression in three plant species in response to treatment with nep1, a fungal protein that causes necrosis. Plant Physiology. 132:1610-1622. Interpretive Summary: Invasive weeds, such as spotted knapweed and dandelion continue to be a major problem for land managers throughout the United States and the world. Bioherbicides that take advantage of the weed's natural pests and pathogens offer environmentally friendly alternatives to chemical weed control measures. Natural products produced by plant pathogens are also being considered as tools for controlling weeds. Nep1 is a protein isolated from the pathogen Fusarium oxysporum. Nep1 causes necrosis in many dicot weed species and has potential as a natural herbicide when applied to weeds as a foliar spray. We have characterized the response of spotted knapweed, dandelion, and arabidopsis to foliar applications of Nep1 using molecular and transmission electron microscopy (TEM) techniques. Using TEM cell damage was observed within one hour after treatment. Changes in expression patterns of plant stress response genes were noted 15 min after treatment in the three weed species studied. The necrosis responses of the three weed species were similar although the amount of damage in response to Nep1 differed between species. By understanding the mode of action of Nep1, the integrated use of Nep1 with other weed control methods can be optimized. This research will be useful to scientists interested in plant microbe interaction and to land managers interested in reducing synthetic chemical used to control weeds.
Technical Abstract: The fungal protein Nep1 causes necrosis when applied to dicotyledonous plants including invasive weeds. Using transmission electron microscopy, it was determined that application of Nep1 to Arabadopsis and two invasive weed species, Centaurea maculosa Lam. (spotted knapweed) and Taraxacum officinale L. (dandelion), caused a reduction in the thickness of the cuticle and a breakdown of chloroplasts 1 to 4 h after treatment. Differential display was used to isolate cDNA clones from the three species showing differential expression in response to Nep1 treatment. Differential gene expression was observed for a putative serpin (CmSER-1) and a calmodulin-like (CmCAL-1) protein from spotted knapweed, and a putative protein phosphatase 2C (ToPP2C-1) and cytochrome P-450 (ToCYP-1) protein from dandelion. Differential expression was observed for genes coding for a putative protein kinase (AtPK-1), a homolog (AtWI-12) of wound induced WI12, a homolog (AtLEA-1) of late embryogenesis abundant LEA-5, a WRKY-18 DNA binding protein (AtWRKY-18), and a phospholipase D (AtPLD-1) from Arabidopsis. Genes showing elevated mRNA levels in Nep1 treated leaves 15 min after Nep1 treatment included CmSER-1 and CmCAL-1 for spotted knapweed, ToCYP-1 and CmCAL-1 for dandelion, and AtPK-1, AtWRKY-18, AtWI-12, and AtLEA-1 for Arabidopsis. Levels of mRNA for AtPLD-1 (Arabidopsis) and ToPP2C-1 (dandelion) decreased rapidly in Silwet-L77 treated plants between 15 min and 4 h of treatment but were maintained or decreased more slowly over time in Nep1 treated leaves. The identified genes are related to gene families involved in plant stress responses including wounding, drought, senescence, and disease resistance.