The potato cyst nematode effector RHA1B is a ubiquitin ligase and uses two distinct mechanisms to suppress plant immune signaling.

Plant pathogens, such as bacteria, fungi, oomycetes and nematodes, rely on wide range of virulent effectors delivered into host cells to suppress plant immunity. Although phytobacterial effectors have been intensively investigated, little is known about the function of effectors of plant-parasitic nematodes, such as Globodera pallida, a cyst nematode responsible for vast losses in the potato and tomato industries. Here, we demonstrate using in vivo and in vitro ubiquitination assays the potato cyst nematode (Globodera pallida) effector RHA1B is an E3 ubiquitin ligase that employs multiple host plant E2 ubiquitin conjugation enzymes to catalyze ubiquitination. RHA1B was able to suppress effector-triggered immunity (ETI), as manifested by suppression of hypersensitive response (HR) mediated by a broad range of nucleotide-binding leucine-rich repeat (NB-LRR) immune receptors, presumably via E3-dependent degradation of the NB-LRR receptors. RHA1B also blocked the flg22-triggered expression of Acre31 and WRKY22, marker genes of pathogen-associated molecular pattern (PAMP)-triggered immunity (PTI), but this did not require the E3 activity of RHA1B. Moreover, transgenic potato overexpressing the RHA1B transgene exhibited enhanced susceptibility to G. pallida. Thus, our data suggest RHA1B facilitates nematode parasitism not only by triggering degradation of NB-LRR immune receptors to block ETI signaling but also by suppressing PTI signaling via an as yet unknown E3-independent mechanism.

Type 1 sensitisation against a Steinernema feltiae product.

The use of biological control measures (biopesticides) is a widespread and fundamental technique for crop protection in greenhouses. Previous reports have documented allergic sensitisation against predatory mites, bacteria and fungi. Till now no cases of sensitisation against nematode products have been described. Two subjects working at a flower greenhouse were examined at the Department of Occupational and Environmental Health at Odense University Hospital. A histamine release test revealed positive reaction against a nematode product containing Steinernema feltiae, but negative reaction when testing formulation ingredients separately. Skin prick testing with samples containing S feltiae or mixed carrier medium, separately, revealed positive reactions in both subjects against S feltiae samples only. Skin prick testing among seven control subjects revealed no positive reactions. This is the first report indicating type 1 sensitivity against a S feltiae product. These findings point to the need for guidelines and preventive measures when handling biopesticide products and biopesticide-treated plants.

Susceptibility and immune response of Deroceras reticulatum, Milax gagates and Limax pseudoflavus exposed to the slug parasitic nematode Phasmarhabditis hermaphrodita.

We exposed three slug species (Deroceras reticulatum (Müller), Milax gagates (Draparnaud) and Limax pseudoflavus L.) to the parasitic nematode Phasmarhabditis hermaphrodita Schneider. P. hermaphrodita was able to cause mortality and feeding inhibition to both D. reticulatum and M. gagates but did not negatively affect L. pseudoflavus. On dissection of surviving L. pseudoflavus large numbers of P. hermaphrodita were found encapsulated in the shell of the slug. We found that by increasing shell size, the slug was able to trap invading nematodes, which could be an immune response to P. hermaphrodita invasion. This is the first report of a slug defense mechanism to inhibit P. hermaphrodita.