No abstract

Salicylic acid (SA) is absolutely required for establishment of acquired resistance in non‐infected tissues following localized challenge of other leaves with a necrotizing pathogen. Although not directly responsive to SA, or induced systemically following pathogen challenge, the expression of defence gene promoter fusions AoPR1—GUS and PAL‐3—GUS after wounding or pathogen challenge could be enhanced by pre‐treating tobacco plants hydroponically with SA, a phenomenon designated ‘potentiation’. Potentiation of AoPR1—GUS wound‐responsiveness was also demonstrated locally, but not systemically, in tobacco tissue exhibiting acquired resistance following infection with either viral or bacterial pathogens. Potentiation of wound‐responsive expression by prior wounding could not be demonstrated. In contrast, potentiation of pathogen‐responsive AoPR1—GUS expression was exhibited both locally and systemically in non‐infected tissue. The spatial and temporal exhibition of defence gene potentiation correlated directly with the acquisition of resistance in non‐infected tissue. Pathogen‐responsive potentiation was obtained at about 10‐fold lower levels of salicylic acid than wounding‐responsive potentiation in AoPR1—GUS tobacco plants prefed with salicylate. These results may explain the failure to observe systemic potentiation of the wound‐responsive defence gene expression. The data suggest a dual role for SA in terms of gene induction in acquired immunity: a direct one by induction of genes such as pathogenesis‐related proteins, and an indirect one by potentiation of expression of other local defence genes (such as PAL and AoPR1) which do not respond directly to SA but become induced on pathogen attack or wounding.

We report the isolation and characterisation of a wound-induced cDNA designated AoPR1 from a suspension of mesophyll cells that had been mechanically isolated from cladodes of light-grown Asparagus officinalis seedlings by grinding in a mortar and pestle. The transcript abundance is up-regulated following cell separation and in chopped mesocotyl tissue from dark-grown seedlings. The expression of AoPR1 was shown by northern analysis to be located around the site of damage. Sequence analysis revealed similarity between the predicted AoPR1 polypeptide and bean PvPR1 and PvPR2 proteins, the potato pSTH2 protein, the pea PI49 protein, the parsley PcPR1-1 protein and a major pollen allergen from birch (BetvI). These transcripts have been shown to be induced in response to microbial attack or fungal elicitation. To our knowledge, this is the first example of a monocot cDNA belonging to this class of intracellular pathogenesis-related proteins (IPRs).

SummaryThe Asparagus officinalis intracellular PR1 (AoPRl) gene is expressed in response to wounding and pathogen attack. We utilized the inverse polymerase chain reaction (IPCR) to isolate the cis-acting regulatory sequences of the AoPRl gene following unsuccessful attempts to identify hybridizing clones in genomic libraries. Sequence analysis of two IPCR products revealed that a 347 bp intron was present in the AoPRl gene and that it was probable that the AoPR7 regulatory sequence had been amplified. To test the AoPRl cis acting sequences for biological function a translational fusion was constructed with the p-glucuronidase (GUS) reporter gene and tested in tobacco. These data demonstrated that sequences 982 bp from the probable start of transcription are sufficient to direct woundinducible transcription and that there is no signal peptide encoded by the first 31 residues of the predicted AoPRl protein. Histochemical localization of GUS activity in transgenic tobacco demonstrated strong activity localized to wound and pathogen invasion sites. GUS activity was also found in mature pollen grains.

BackgroundDevelopment and evaluation of new insect pest management tools is critical for overcoming over-reliance upon, and growing resistance to, synthetic, biological and plant-expressed insecticides. For transgenic crops expressing insecticidal proteins from the bacterium Bacillus thuringiensis (‘Bt crops’) emergence of resistance is slowed by maintaining a proportion of the crop as non-Bt varieties, which produce pest insects unselected for resistance. While this strategy has been largely successful, multiple cases of Bt resistance have now been reported.One new approach to pest management is the use of genetically engineered insects to suppress populations of their own species. Models suggest that released insects carrying male-selecting (MS) transgenes would be effective agents of direct, species-specific pest management by preventing survival of female progeny, and simultaneously provide an alternative insecticide resistance management strategy by introgression of susceptibility alleles into target populations. We developed a MS strain of the diamondback moth, Plutella xylostella, a serious global pest of crucifers. MS-strain larvae are reared as normal with dietary tetracycline, but, when reared without tetracycline or on host plants, only males will survive to adulthood. We used this strain in glasshouse-cages to study the effect of MS male P. xylostella releases on target pest population size and spread of Bt resistance in these populations.ResultsIntroductions of MS-engineered P. xylostella males into wild-type populations led to rapid pest population decline, and then elimination. In separate experiments on broccoli plants, relatively low-level releases of MS males in combination with broccoli expressing Cry1Ac (Bt broccoli) suppressed population growth and delayed the spread of Bt resistance. Higher rates of MS male releases in the absence of Bt broccoli were also able to suppress P. xylostella populations, whereas either low-level MS male releases or Bt broccoli alone did not.ConclusionsThese results support theoretical modeling, indicating that MS-engineered insects can provide a powerful pest population suppressing effect, and could effectively augment current Bt resistance management strategies. We conclude that, subject to field confirmation, MS insects offer an effective and versatile control option against P. xylostella and potentially other pests, and may reduce reliance on and protect insecticide-based approaches, including Bt crops.