Hogenhout, S. | Search bioRxiv

bioRxiv2020

Candidatus (Ca.) phytoplasma asteris subgroups display distinct disease progression dynamics during the carrot growing season

Aster Yellows phytoplasma (AYp; Candidatus (Ca.) Phytoplasma asteris) is an obligate bacterial pathogen that is the causative agent of multiple diseases in herbaceous plants. While this phytoplasma has been examined in depth for its disease characteristics, knowledge about the spatial and temporal dynamics of pathogen spread is lacking. The phytoplasma is found in plants phloem and is vectored by leafhoppers (Cicadellidae: Hemiptera), including the aster leafhopper, Macrosteles quadrilineatus Forbes. The aster leafhopper is a migratory insect pest that overwinters in the southern United States, and historical data suggest these insects migrate from southern overwintering locations to northern latitudes annually, transmitting and driving phytoplasma infection rates as they migrate. A more in-depth understanding of the spatial, temporal and genetic determinants of Aster Yellows disease progress will lead to better integrated pest management strategies for Aster Yellows disease control. Carrot, Daucus carota L., plots were established at two planting densities in central Wisconsin and monitored during the 2018 growing season for Aster Yellows disease progression. Symptomatic carrots were sampled and assayed for the presence of the Aster Yellows phytoplasma. Aster Yellows disease progression was determined to be significantly associated with calendar date, crop density, location within the field, and phytoplasma subgroup.

ecology↗

bioRxiv2017

Fishing for New Bt Receptors in Diamondback Moth

Bt toxins bind to receptors in the brush border membrane of the insect gut and create pores, leading to insect death. Bt-resistant insects demonstrate reduced binding of the Bt toxins to gut membranes. However, our understanding of the gut receptors involved in Bt toxin binding, and which receptors confer resistance to these toxins is incomplete, especially in diamondback moth (Plutella xylostella), a major agricultural pest. Identifying receptors has remained challenging because we lack sufficiently sensitive methods to detect Bt receptor interactions. Here, we report a modified far-immunoblotting technique, which revealed a broad spectrum of binding targets for the Bt toxins Cry1Ac, Cry1Ab, and Cry1Bd in diamondback moth. We confirm the role of the glucosinolate sulfatases GSS1 and GSS2 in Cry1Bd toxicity. GSS1 and GSS2 bind directly to Cry1Bd, and their expression is crucial for Cry1Bd toxicity. These results improve our understanding of the molecular mechanisms of Bt toxicity.\n\nAUTHOR SUMMARYThe Bt toxins, from the soil bacterium Bacillus thuringiensis, have wide applications in agriculture as insecticides applied to plants or expressed in genetically modified crops. Bt toxins bind to receptors in the brush border membrane of the insect gut and create pores leading to insect death. The success of the Bt toxins in controlling insect pests has been hindered by the emergence of resistant insects, which show reduced binding of Bt to their gut membranes. Although ongoing research has identified a few receptors, many remain unknown and the mechanisms by which these receptors cause resistance remain unclear. Here, we used a modified far-immunoblotting technique to identify proteins that bind to the toxins Cry1Ac, Cry1Ab, and Cry1Bd in the diamondback moth. This identified two glucosinolate sulfatases that bind directly to Cry1Bd; also, the toxicity of Cry1Bd requires expression of these glucosinolate sulfatases. Therefore, identification of these candidate receptors improves our understanding of Bt function and resistance.

biochemistry↗