Projects
Mechanisms mediating viral ‘recognition’ of insect vectors
Previously I demonstrated that Turnip mosaic virus (TuMV) infection of host plants increases insect vector attraction to and reproduction on host plants. Changes in host physiology that mediated host-vector interactions were due to the expression of a single viral protein, NIa-Pro. Recently we determined that NIa-Pro relocalizes from the nucleus to the vacuole of the plant cell in the presence of the insect vector. Importantly, NIa-Pro needs to relocalize in order to inhibit plant defenses during infection. These results suggest that plant viruses respond actively to the presence of insect vectors, promoting insect performance and transmission only when needed. The NSF recently funded my lab to continue this project as a Plant Genome Early Career Award (NSF PGRP 2018-2023). The primary focus of the grant is to develop a detailed understanding of the genes and pathways that underlie viral ‘recognition’ of insect vectors and changes in the host plant physiology.
Circulative, non-propagative virus transmission
In 2014, I was funded by the USDA-NIFA to investigate the mechanisms mediating Potato leafroll virus (PLRV)-plant-vector interactions ($150,000 to Casteel lab; 2014-2015). PLRV is phloem-limited and transmitted by aphid vectors in a circulative, non-propagative manner. This means that the virus must be acquired through the insect gut and exit through the salivary gland during feeding with no replication in the insect. We hypothesize that PLRV uses very different mechanisms to alter plant physiology compared to TuMV, which is not phloem-limited and is not transmitted in the same manner. We determined that P7 from PLRV’s genome mediates changes in plant chemistry and plant defense. We are currently investigating the function of this protein in more detail and a manuscript from this work is currently in review. My interest in circulative non-propagative viruses continues through a recent collaboration with Dr. Dave Crowder at Washington State University in Pullman, WA. The focus of the project is to determine the impact of non-vector herbivores on Pea enation mosaic virus (PEMV) outbreaks in legume cropping systems (USDA-NIFA 2017-2020). For this project, we are using field and lab experiments combined with genetics and plant chemistry to determine relevant mechanisms.
VIPER: Viruses and insects as plant enhancement resources
Crops face numerous biotic and abiotic challenges in the field each growing season, which are often difficult to predict. To combat these challenges, growers depend on chemical sprays, selective breeding, and, in some cases, transgenic approaches such as Bacillus thuringiensis (Bt) toxins. Unfortunately, chemical sprays are expensive and may have negative environmental effects. While resistant cultivars and transgenic plants are more environmentally friendly, they cannot be developed fast enough to counter new threats that arise during a growing season. Moreover, there are often negative impacts on yield observed in resistant plants when the challenge is not present. My lab received funding to address these challenges as part of a large multi-institutional project led by Dr. Georg Jander at The Boyce Thompson Institute ($10.3 million; Defense Advanced Research Projects Agency). My lab specifically is engineering potyviruses, potexviruses and insect vectors to enhance drought tolerance in mature maize plants through transgene expression and gene silencing. This will allow growers to rapidly genetically engineer crops in a single growing season and adapt to changing threats each year. (DARPA 2017-2021).
Integrating soil and pest management for healthy agro-ecosystems
Lower insect pest populations found on long-term organic farms have largely been attributed to increased biodiversity and abundance of beneficial predators. However, potential induction of plant defenses has largely been ignored. Recently we determined host plant resistance also mediates decreased pest populations in organic systems. We demonstrated that greater numbers of leafhoppers (Circulifer tenellus) settle on tomatoes (Solanum lycopersicum) grown using conventional management as compared to organic. Soil microbiome sequencing, chemical analysis, and transgenic approaches, coupled with multi-model inference, suggest that changes in leafhopper settling between organically and conventionally-grown tomatoes are dependent on salicylic acid accumulation in the plant, likely mediated by rhizosphere microbial communities. These results suggest that organically-managed soils and microbial communities may play an unappreciated role in reducing plant attractiveness to pests by increasing plant resistance. This project is not funded but we plan to submit a NSF grant in 2020 and I would be happy to have your help in this effort or on a fellowship related to this project.
The paper is submitted and available on BioRx:
https://www.biorxiv.org/content/10.1101/787549v1