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1.  Jasmonate-dependent plant defense restricts thrips performance and preference 
BMC Plant Biology  2009;9:97.
The western flower thrips (Frankliniella occidentalis [Pergande]) is one of the most important insect herbivores of cultivated plants. However, no pesticide provides complete control of this species, and insecticide resistance has emerged around the world. We previously reported the important role of jasmonate (JA) in the plant's immediate response to thrips feeding by using an Arabidopsis leaf disc system. In this study, as the first step toward practical use of JA in thrips control, we analyzed the effect of JA-regulated Arabidopsis defense at the whole plant level on thrips behavior and life cycle at the population level over an extended period. We also studied the effectiveness of JA-regulated plant defense on thrips damage in Chinese cabbage (Brassica rapa subsp. pekinensis).
Thrips oviposited more on Arabidopsis JA-insensitive coi1-1 mutants than on WT plants, and the population density of the following thrips generation increased on coi1-1 mutants. Moreover, thrips preferred coi1-1 mutants more than WT plants. Application of JA to WT plants before thrips attack decreased the thrips population. To analyze these important functions of JA in a brassica crop plant, we analyzed the expression of marker genes for JA response in B. rapa. Thrips feeding induced expression of these marker genes and significantly increased the JA content in B. rapa. Application of JA to B. rapa enhanced plant resistance to thrips, restricted oviposition, and reduced the population density of the following generation.
Our results indicate that the JA-regulated plant defense restricts thrips performance and preference, and plays an important role in the resistance of Arabidopsis and B. rapa to thrips damage.
PMCID: PMC2724403  PMID: 19635132
2.  Arabidopsis-thrips system for analysis of plant response to insect feeding 
Plant Signaling & Behavior  2008;3(7):446-447.
Insect feeding retards plant growth and decreases crop productivity. Plants respond to insect feeding at the molecular, cellular and physiological levels. The roles of the plant hormones jasmonic acid (JA), ethylene (ET) and salicylic acid (SA) in plant responses to insect feeding have been studied. However, these studies are focused on the plant responses to feeding by well-studied caterpillar type insects or aphid pests. In contrast, we have focused on a minute insect pest, the western flower thrips (Frankliniella occidentalis). Analyses of the responses of hormone-related mutants of Arabidopsis (i.e., JA-insensitive mutant coi1-1, ET-insensitive mutants ein2-1 and ein3-1, and SA-deficient mutant eds16-1) and transcriptome-based comparative analyses indicate the central role of JA in plant responses to thrips feeding. Our work clearly shows that JA signaling, but not JA/ET signaling, is involved in plant tolerance to thrips feeding. We intend to examine the utility and suitability of the Arabidopsis-thrips system in studies of plant responses to insect feeding.
PMCID: PMC2634423  PMID: 19704479
Arabidopsis thaliana; ethylene; Frankliniella occidentalis; insect feeding; jasmonate; western flower thrips
3.  Antiviral RNA Silencing Is Restricted to the Marginal Region of the Dark Green Tissue in the Mosaic Leaves of Tomato Mosaic Virus-Infected Tobacco Plants▿  
Journal of Virology  2008;82(7):3250-3260.
Mosaic is a common disease symptom caused by virus infection in plants. Mosaic leaves of Tomato mosaic virus (ToMV)-infected tobacco plants consist of yellow-green and dark green tissues that contain large and small numbers of virions, respectively. Although the involvement of RNA silencing in mosaic development has been suggested, its role in the process that results in an uneven distribution of the virus is unknown. Here, we investigated whether and where ToMV-directed RNA silencing was established in tobacco mosaic leaves. When transgenic tobaccos defective in RNA silencing were infected with ToMV, little or no dark green tissue appeared, implying the involvement of RNA silencing in mosaic development. ToMV-related small interfering RNAs were rarely detected in the dark green areas of the first mosaic leaves, and their interior portions were susceptible to infection. Thus, ToMV-directed RNA silencing was not effective there. By visualizing the cells where ToMV-directed RNA silencing was active, it was found that the effective silencing occurs only in the marginal regions of the dark green tissue (∼0.5 mm in width) and along the major veins. Further, the cells in the margins were resistant against recombinant potato virus X carrying a ToMV-derived sequence. These findings demonstrate that RNA silencing against ToMV is established in the cells located at the margins of the dark green areas, restricting the expansion of yellow-green areas, and consequently defines the mosaic pattern. The mechanism of mosaic symptom development is discussed in relation to the systemic spread of the virus and RNA silencing.
PMCID: PMC2268452  PMID: 18216118
4.  Tomato Mosaic Virus Replication Protein Suppresses Virus-Targeted Posttranscriptional Gene Silencing 
Journal of Virology  2003;77(20):11016-11026.
Posttranscriptional gene silencing (PTGS), a homology-dependent RNA degradation system, has a role in defending against virus infection in plants, but plant viruses encode a suppressor to combat PTGS. Using transgenic tobacco in which the expression of green fluorescent protein (GFP) is posttranscriptionally silenced, we investigated a tomato mosaic virus (ToMV)-encoded PTGS suppressor. Infection with wild-type ToMV (L strain) interrupted GFP silencing in tobacco, coincident with visible symptoms, whereas some attenuated strains of ToMV (L11 and L11A strains) failed to suppress GFP silencing. Analyses of recombinant viruses containing the L and L11A strains revealed that a single base change in the replicase gene, which causes an amino acid substitution, is responsible for the symptomless and suppressor-defective phenotypes of the attenuated strains. An agroinfiltration assay indicated that the 130K replication protein acts as a PTGS suppressor. Small interfering RNAs (siRNAs) of 21 to 25 nucleotides accumulated during ToMV infection, suggesting that the major target of the ToMV-encoded suppressor is downstream from the production of siRNAs in the PTGS pathway. Analysis with GFP-tagged recombinant viruses revealed that the suppressor inhibits the establishment of the ToMV-targeted PTGS system in the inoculated leaves but does not detectably suppress the activity of the preexisting, sequence-specific PTGS machinery there. Taken together, these results indicate that it is likely that the ToMV-encoded suppressor, the 130K replication protein, blocks the utilization of silencing-associated small RNAs, so that a homology-dependent RNA degradation machinery is not newly formed.
PMCID: PMC224966  PMID: 14512550

Results 1-4 (4)