An Alternative Bioassay for Synchytrium endobioticum Demonstrates the Expression of Potato Wart Resistance in Aboveground Plant Parts.

The obligate biotrophic chytrid species Synchytrium endobioticum is the causal agent of potato wart disease. Currently, 39 pathotypes have been described based on their interaction with a differential set of potato varieties. Wart resistance and pathotyping is performed using bioassays in which etiolated tuber sprouts are inoculated. Here, we describe an alternative method in which aboveground plant parts are inoculated. Susceptible plants produced typical wart symptoms in developing but not in fully expanded aboveground organs. Colonization of the host by S. endobioticum was verified by screening for resting spores by microscopy and by molecular techniques using TaqMan polymerase chain reaction and RNAseq analysis. When applied to resistant plants, none of these symptoms were detectable. Recognition of S. endobioticum pathotypes by differentially resistant potato varieties was identical in axillary buds and the tuber-based bioassays. This suggests that S. endobioticum resistance genes are expressed in both etiolated "belowground" sprouts and green aboveground organs. RNAseq analysis demonstrated that the symptomatic aboveground materials contain less contaminants compared with resting spores extracted from tuber-based assays. This reduced microbial contamination in the aboveground bioassay could be an important advantage to study this obligate biotrophic plant-pathogen interaction. Because wart resistance is active in both below- and aboveground organs, the aboveground bioassay can potentially speed up screening for S. endobioticum resistance in potato breeding programs because it omits the requirement for tuber formation. In addition, possibilities arise to express S. endobioticum effectors in potato leaves through agroinfiltration, thereby providing additional phenotyping tools for research and breeding. Copyright © 2019 The Author(s). This is an open access article distributed under the CC BY 4.0 International license .

The effect of immunotoxins directed against CD80 and CD86 on primary T-cell alloresponses.

Activation of primary resting T cells requires costimulation which can be delivered by the B7 molecules (CD80 and CD86) expressed on activated antigen-presenting cells (APC). In the present study, we examined in vitro effects of immunotoxins (ITs) composed of gelonin conjugated to mAbs against CD80 or CD86 (alphaCD80-IT and alphaCD86-IT). The specificity of both ITs was demonstrated using CD80 and CD86 transfected cell lines. In primary mixed lymphocyte cultures (MLCs), it was found that the average inhibitory capacity of alphaCD86-IT (72%) and alphaCD80-IT (30%) was significantly higher than alphaCD86 (54%) and alphaCD80 (11%). In reculture MLC experiments it was found that peripheral blood mononuclear cells pretreated with alphaCD86/alphaCD80 regained full stimulatory capacity whereas alphaCD86-IT/alphaCD80-IT pretreatment induced >95% loss of stimulatory capacity. Our results therefore demonstrate that these alphaB7-ITs functionally block B7-CD28 costimulatory signaling and eliminate activated APC.