Genetic Insights from Pennycress: Enhancing Canola Resistance to Verticillium longisporum
Term: 3 years
Status: Ongoing
Researcher(s): Hossein Borhan, Isobel Parkin, Kevin Rozwadowski, Peng Gao, AAFC; Lingling Jin, U of S
SaskOilseeds Investment: $40,166.67
Total Project Cost: $241,000
Funding Partners: WGRF, ACPC, MCGA
Objective
Defense pathways against V. longisporum will be defined using pennycress as a model plant.
Resistance genes against V. longisporum in pennycress will be identified.
The knowledge gained by the pennycress-verticillium model system will be applied to improve the B. napus resistance to V. longisporum.
Project Description
Although a relatively new disease of concern for Canadian canola producers (1), verticillium stripe (VS) is an important disease for the European canola growers and has been extensively studied over the past several decades (2). The Verticillium longisporum (Vls) research on canola by European scientists has mainly centred on pathology, disease management and epidemiology (3).
On the contrary, genetics and genomics of canola resistance and Vls virulence have only received attention in the past decade. Since first detected in Manitoba in 2014, the spread of Vls across the prairies and reports of severe infection and considerable yield loss have made VS a disease of concern and research on genetics of canola resistance to Vls a top priority to protect canola production. However, the high number of Brassica QTLs for resistance to Vls, reported recently, indicates the complexity of Vls-Brassica interaction and the challenges in breeding resistance to VS disease.
The natural genetic diversity of wild plant species is a treasure trove of novel genes to enrich the narrow gene pool of domesticated crops and to genetically enhance crops against biotic and abiotic stress. Naturally occurring R gene and chemically induced defence mutants in the well-established model plant Arabidopsis thaliana (At) have been applied to genetically enhance resistance to pathogens in various crops. Some examples of the application of R genes from Arabidopsis are the use of AtWRR4 to protect Brassica sp. against the oomycete pathogen Albugo candida and Arabidopsis RPS4 and RPS1 that confer resistance to fungal and bacterial pathogens in transgenic Brassica, tomato and cucumber. Among many defence genes identified by screening mutagenized A. thaliana seeds, the AtNPR1 and AtDMR6 genes are two prominent examples that have been successfully used to enhance immunity in various crops.
Another wild species relative of Brassica crops is Thlaspi arvense, commonly known as pennycress, a cruciferous weed widely spread across Canada and the US. Pennycress has been reported as a natural host of Vls. In addition, pennycress is a diploid species with a small genome, is easily transformed, has a sequenced genome and other genetic tools available, such as gene editing and a sequenced EMS mutagenized population, collectively making pennycress a desirable model plant for biotic and abiotic stress research in the Brassicaceae. In fact, in our experience, pennycress is a more suitable model plant and source of resistance genes for some of the canola pathogens than the widely used cruciferous model species A. thaliana. For example, A. thaliana morphology and immune response make it unsuitable to study genetics of blackleg and clubroot diseases. Our research and others have failed to identify Arabidopsis accessions susceptible to blackleg or resistant to clubroot. Moreover, the small stature of A. thaliana makes blackleg and clubroot disease evaluation very difficult.
We have acquired a germplasm collection of 300 pennycress accessions, the majority collected from Canada and the US, as well as an EMS mutagenized population of pennycress. Biotic research using model plants is particularly helpful in understanding the genetics of pathogens and crop species with a complex genome. An example is the challenging Vls-canola pathosystem due to the complexity associated with the allodiploid Vls and the allotetraploid B. napus genomes. Genetic studies by our labs and others indicate the B. napus resistance to Vls is controlled by multiple minor genes (QTL) making it difficult to accurately identify the Vls-QTLs. Another limitation to the direct use of B. napus is that tools such as EMS mutagenesis, gene transformation and gene editing, essential to the discovery of novel genes and decoding canola’s immunity, cannot be readily and rapidly applied to genetically complex species such as B. napus.
Translation of research from model to crop species requires rapid and high throughput gene function validation in the crop, a tool that did not exist for Brassica species. Fortunately, Dr. Rozwadowski has developed a series of virus vectors that allows virus-induced gene silencing (VIGS) and transient gene over-expression without the need for tedious and time-consuming stable canola transformation. These vectors allow rapid cloning using the highly efficient Golden Gate cloning method and high throughput delivery of the virus into Brassica via seed infiltration.
Here we propose to utilize the existing resources and build on our preliminary research on the Vls-pennycress pathosystem to unravel the genetic basis of resistance against verticillium stripe and apply these findings to improve canola's resistance to Vls, a priority identified by the Canola Council of Canada's to protect canola against VS.