Molecular and histochemical characterisation of two distinct poplar Melampsora leaf rust pathosystems.

In this study, we compared interactions of two Melampsora foliar rust species with poplar, which resulted in either limited or abundant pathogen proliferation. In the pathosystem exhibiting limited pathogen growth, a defence response was observed after invasion of poplar leaf tissues by the biotroph, with late and clear production of reactive oxygen species (ROS) and other products. Characterisation of the histological, biochemical and transcriptional events occurring in both pathosystems showed striking similarity with components of plant defence reactions observed during qualitative resistance. Key components associated with development of an active defence response, such as up-regulation of pathogenesis-related (PR) genes, were observed during infection. Moreover, the time course and strength of gene induction appear to be critical determinants for the outcome of the tree-pathogen interaction. This work provides basic biochemical characterisation and expression data for the study of so-called partial resistance in the poplar-rust pathosystem, which is also applicable to other plant-pathogen interactions resulting in quantitative disease resistance.

Inducible expression of the heterologous PAL2 promoter from bean in white pine (Pinus strobus) transgenic cells.

To elucidate heterologous promoter function in gymnosperms, we introduced the bean phenylalanine ammonia-lyase-beta-glucuronidase (PAL2-GUS) gene fusion into white pine (Pinus strobus L.). Over 15 lines were produced and integration of Agrobacterium T-DNA was confirmed by Southern analysis. Induction of the reporter gene was detected in all of the lines tested following UV illumination. In contrast, a weak but constant induction was seen in only a few lines following treatment with salicylic acid (SA) or jasmonic acid (JA). However, pretreatment of suspension cultures with SA or JA enhanced the induction of PAL2-GUS expression by UV irradiation. This specific enhancement or potentiation was reduced by 50% by treating the cells with indomethacin, an inhibitor of phospholipase activity, suggesting that the observed potentiation of UV induction involves the octadecanoid pathway. The UV induction was completely abolished by treating the cells with okadaic acid, an inhibitor of phosphatase activity. Thus, the induction of the heterologous PAL2 promoter from bean is consistent with the induction of phenylalanine ammonia-lyase (PAL) in angiosperms. Furthermore, our findings suggest that conifers, although phylogenetically distant to angiosperms, share some conserved promoter elements and some signal transduction mechanisms for UV-light perception.

Agrobacterium tumefaciens-mediated transformation of hybrid larch (Larix kaempferi T L. decidua) and transgenic plant regenerationn.

A transformation procedure was developed for hybrid larch embryogenic tissue using Agrobacterium tumefaciens. The cocultivation procedure yielded one to two transformation events per 100 cocultivated masses. The addition of 100 µM coniferyl alcohol increased the yield. This improved procedure was successfully applied to three other genotypes. After 3 months on selective medium, the transgenic tissue remained embryogenic, which allowed production of transgenic plants in the greenhouse. Stable integration of the transgene was confirmed by PCR and Southern hybridisation on transformed tissues and acclimatised plants.