Expression of potato multicystatin in florets of chrysanthemum and assessment of resistance to western flower thrips, Frankliniella occidentalis

The gene of the 85 kDa cysteine protease inhibitor (CPI) potato multicystatin (PMC), was PCR-cloned and expressed under the control of the UEP1 promoter in chrysanthemum (Dendranthema grandiflora). Over 30 independent transgenic plant lines were analysed for PMC expression in florets by immunoassay and a selection of those for papain inhibitor activity (PIA). A significant correlation between PIA activity and PMC expression levels was established demonstrating that the highest expressers raised the concentration of PIA to 0.28 pmol/μg from an endogenous background level of 0.15 pmol/μg. On this basis, the PMC gene was estimated to be expressed at a level of 0.13␘f total protein. Some of the transgenic lines exhibited up to 5-fold higher levels of PIA (0.82 pmol/μg protein). This did not correlate with the immunological data, however, and may be the result of frequently occurring somaclonal variation. A non-choice bioassay of 7-10 days on whole flowers was carried out to study the effect of PMC on the fecundity of Western Flower Thrips in terms of the number of larvae produced. No correlation between the reduction in the oviposition rate and PMC expression could be established, which may be due to the relatively low expression level of PMC in chrysanthemum. The transgenic lines with the highest levels of endogenous PIA also had the lowest thrips reproduction rates, but further experiments are required to exclude artefacts caused by the aberrant phenotype.