Transcriptional Dynamics in Resistant Chinese and Susceptible American Chestnut Roots During Early Response to Phytophthora Cinnamomi Infection

Title: Transcriptional dynamics in resistant Chinese and susceptible American chestnut roots during early response to Phytophthora cinnamomi infection PI: Ellen Crocker, Department of Forestry and Natural Resources, University of Kentucky Funding source: The American Chestnut Foundation (TACF) Summary: Restoration of the American chestnut will require introducing resistance to two major pathogens, Cryphonectria parasitica (Cp) and Phytophthora cinnamomi (Pc), which cause chestnut blight and root rot/ink disease, respectively. Recent success in developing blighttolerant American chestnut transformed with an oxalate oxidase gene from wheat has shown that genetic engineering is a feasible approach for restoration of American chestnut in the northern portion of its range. However, in the southeastern US, where trees suffer from ink disease, pyramiding resistance to both Cp and Pc is crucial for bringing American chestnut back to the forest. The paucity of information on genetics of resistance to Pc in chestnut is one of the limiting factors for efficient incorporation of resistance genes into American chestnut via traditional breeding and/or genetic engineering. To address this gap in knowledge, we previously investigated the genetic control of resistance to Pc in interspecific crosses derived from two Chinese sources, ‘Mahogany’ and ‘Nanking’. Three major QTL intervals were localized on saturated genetic maps and delineated on pseudochromosomes on the assembled Chinese chestnut (‘Vanuxem’) genome. A genome-wide scan for footprints of natural selection in a set of resistant (near immune) Chinese chestnut trees revealed a list of 36 genes under negative selection within QTL intervals. We considered these genes to be likely candidates for control of the trait in ‘Mahogany” and ‘Nanking’ backgrounds – the two main Chinese sources of resistance in the TACF breeding program. Here, we propose comparative gene expression profiling of American and Chinese chestnut trees during early response to infection with Pc zoospores. Based on the published literature and our previous experiments, we selected 3, 6, 12 and 24 hours after inoculation with Pc zoospores as the most useful time-points to reveal molecular networks associated with the contrasting responses of Chinese and American chestnut roots to pathogen exposure. We expect that time-course transcriptomic data superimposed with genetic information from previous studies will narrow down a list of candidate genes for functional characterization, as well as pinpoint other key components of the defensive molecular network that were not detected in hybrid material has been used in genetic analyses. Funds will be used for salary (Tetyana Zhebentyayeva) to support RNAseq project in chestnut showing which genes are causing differential resistance between Chinese (resistant) and American (susceptible) chestnuts.