Hydroperoxide lyase depletion in transgenic potato plants leads to an increase in aphid performance

Hydroperoxide lyases (HPLs) catalyze the cleavage of fatty acid hydroperoxi des to aldehydes and oxoacids, These volatile aldehydes play a major role i n forming the aroma of many plant fruits and flowers. In addition, they hav e antimicrobial activity in vitro and thus are thought to be involved in th e plant defense response against pest and pathogen attack. An HPL activity present in potato leaves has been characterized and shown to cleave specifi cally 13-hydroperoxides of both linoleic and linolenic acids to yield hexan al and 3-hexenal, respectively, and 12-oxo-dodecenoic: acid. A cDNA encodin g this HPL has been isolated and used to monitor gene expression in healthy and mechanically damaged potato plants. HPL gene expression is subject to developmental control, being high in young leaves and attenuated in older o nes, and it is induced weakly by wounding. HPL enzymatic activity, neverthe less, remains constant in leaves of different ages and also after wounding, suggesting that posttranscriptional mechanisms may regulate its activity l evels. Antisense-mediated HPL depletion in transgenic potato plants has ide ntified this enzyme as a major route of 13-fatty acid hydroperoxide degrada tion in the leaves. Although these transgenic plants have highly reduced le vels of both hexanal and 3-hexenal, they show no phenotypic differences com pared with wild-type ones, particularly in regard to the expression of woun d-induced genes. However, aphids feeding on the HPL-depleted plants display approximately a two-fold increase in fecundity above those feeding on nont ransformed plants, consistent with the hypothesis that HPL-derived products have a negative impact on aphid performance. Thus, HPL-catalyzed productio n of C6 aldehydes may be a key step of a built-in resistance mechanism of p lants against some sucking insect pests.