Host Resistance to Parasitic Plants-Current Knowledge and Future Perspectives.

Parasitic flowering plants represent a diverse group of angiosperms, ranging from exotic species with limited distribution to prominent weeds, causing significant yield losses in agricultural crops. The major damage caused by them is related to the extraction of water and nutrients from the host, thus decreasing vegetative growth, flowering, and seed production. Members of the root parasites of the Orobanchaceae family and stem parasites of the genus Cuscuta are among the most aggressive and damaging weeds, affecting both monocotyledonous and dicotyledonous crops worldwide. Their control and eradication are hampered by the extreme seed longevity and persistence in soil, as well as their taxonomic position, which makes it difficult to apply selective herbicides not damaging to the hosts. The selection of resistant cultivars is among the most promising approaches to deal with this matter, although still not widely employed due to limited knowledge of the molecular mechanisms of host resistance and inheritance. The current review aims to summarize the available information on host resistance with a focus on agriculturally important parasitic plants and to outline the future perspectives of resistant crop cultivar selection to battle the global threat of parasitic plants.

Functional Characterization of the Photosynthetic Machinery in Smicronix Galls on the Parasitic Plant Cuscuta campestris by JIP-Test.

Members of the genus Cuscuta are generally considered to be non-photosynthetic, stem-holoparasitic flowering plants. Under certain circumstances, at least some members of the genus are capable of limited photosynthesis. The galls of the Smicronyx weevils formed on Cuscuta campestris are particularly rich in chlorophylls compared to the stem of the parasitic plant. In the present study, we aimed to characterize the photosynthetic activity in the inner and outer gall cortices in comparison to the non-photosynthetic stems and a reference plant (Arabidopsis thaliana). The recorded prompt chlorophyll fluorescence transients were analyzed using JIP test. Detailed analysis of the chlorophyll fluorescence confirmed the presence of actively functioning photosynthetic machinery, especially in the inner cortex of the galls. This photosynthesis, induced by the insect larvae, did not reach the levels of the photosynthetic activity in Arabidopsis thaliana plants. Thylakoid protein complexes were identified by separation with two-dimensional Blue Native/SDS PAGE. It appeared that some of the complexes presented in A. thaliana are missing in C. campestris. We hypothesize that the insect-triggered transition from non-photosynthetic to photosynthetic tissue in the gall is driven by the increased requirements for nutrients related to the larval nutrition.

Salinity effect on Cuscuta campestris Yunck. Parasitism on Arabidopsis thaliana L.

Stem holoparasitic flowering plants of the genus Cuscuta are globally distributed invasive species and agricultural pests. The present research represents the combined effect of salt stress (e.g. abiotic stress) and Cuscuta campestris infection (e.g. biotic stress) on the model host plant Arabidopsis thaliana and the response of the parasite to salinity. The response of these parasites to abiotic stress conditions including salinity is poorly studied. Arabidopsis plants were continuously irrigated with 0, 50 and 150 mM NaCl and subjected to C. campestris infection. The influence of both abiotic and biotic stresses on the major osmoprotectant L-proline and three antioxidant enzymes - catalase, superoxide dismutase and guaiacol peroxidase, was assessed in both the parasite and the host plant. All four biochemical markers were differentially affected by stress, showing that the influence of C. campestris parasitism and its interaction with salinity is mostly in the site of infection (direct response) and also in roots (indirect vertical response) rather than on non-infected leaves of infected plants (indirect horizontal response). Despite its absence of soil contact, C. campestris was also significantly affected by salinity (indirect response). The mutual adaptation of the parasite-host pair to salinity slightly altered the regular response to abiotic stress of A. thaliana, but no detrimental additive effect of biotic and abiotic stress was observed.

Metabolic and functional distinction of the Smicronyx sp. galls on Cuscuta campestris.

MAIN CONCLUSION: The weevil gall contains two distinct regions, differing in hydrolytic and antioxidant enzymes activity and profiles, which is also functionally distinct from the non-infected Cuscuta stems. Weevils of the genus Smicronyx are gall-forming insects, widely distributed on parasitic flowering plants of the genus Cuscuta. Thus, they are considered epiparasites and potential method for biological control of their agriculturally harmful hosts. Although several reports on gall formation in Cuscuta spp. exist, the metabolic and functional changes, occurring in the gall, remained largely unknown. Smicronyx sp. galls, collected from a wild Cuscuta campestris population, were dissected into two distinct regions, inner and outer cortex, defined by the higher chlorophyll content of the inner cortex. Based on hydrolytic and antioxidant enzymes activity and isoenzymatic profiles as analyzed after electrophoretic separation, we suggested that the gall differs in its metabolic activity from the non-infected plant tissue. While the outer cortex serves as a region of nutrient storage and mobilization, the inner cortex is directly involved in larvae nutrition. The increase in metabolic activity resulted in significantly increased superoxide dismutase activity in the gall, while several other antioxidant enzymes diminished. The present research offers new insights into the functionally differing regions of Smicronyx galls and the metabolic changes, induced in C. campestris in result of the gall formation.