Crops are susceptible to a multitude of diseases, some of the most devastating being caused by microscopic fungi. Plant pathogenic fungi and their hosts are locked in a battle, the outcome of which is strongly influenced by their genetic attributes. Understanding the interplay between host and pathogen gene expression and gene function provides an unparalleled insight into how infection occurs and thus how disease formation might be disrupted.
In cereal crops, one of the most serious diseases to re-emerge globally in the past 20 years is Fusarium Head Scab / Ear Blight. This floral disease results in reduced grain yield and lower grain quality due to contamination with various harmful trichothecene mycotoxins. Globally the most prevalent and important species to infect wheat crops is Fusarium graminearum (Fg). Like many other plant pathogens, Fg is predicted to produce in planta an array of small secreted effector proteins that modulate plant metabolism to suppress and/ or re-programme plant defences, thereby promoting infection . During compatible interactions with the wheat spike, the advancing Fg hyphae colonise extracellular spaces in wheat rachis tissue without causing macroscopic symptoms. Later, hyphal penetration of wheat cells coincides with the induction of host cell death . Detailed analysis of the Fg genome / pan-genome as well as the characterisation of early Fg transcriptome during symptomless wheat infection has led to the identification of two classes of small secreted Fg effectors and several in planta only expressed secondary metabolite gene clusters [3.4]. To explore function, the candidate small secreted effectors were transiently overexpressed using the Barley Stripe Mosaic Virus vector system (BSMV-VOX) and shown to either enhance or supress Fg fungal infections.
Globally, severe difficulties are routinely encountered when attempting to control Fusarium floral infections in wheat using fungicides and/or natural resistance mediated by major quantitative trait loci (QTLs). A novel disease control solution under evaluation is Host-Induced Gene Silencing (HIGS) . Two recently published independent studies have revealed that transgenic plants expressing RNAi silencing constructs that specifically target essential Fg genes, such as cytochrome P450 lanosterol C-14α-demethylase (CYP51) or chitin synthase, display high levels of resistance to this pathogen [6,7]. In a new collaborative project with EMBRAPA in Brazil, we have re-analysed the predicted sub-set of Fg genes expressed during the symptomless infection phase and are now in a position to target additional Fg genes that are considered ‘essential for life’ or required for virulence towards wheat . Transgenic wheat and Arabidopsis plants harbouring specific RNAi gene combinations have been generated and these will be functionally and molecularly characterised in the T1 and T2 generations throughout 2018.
References: 1. Dean et al. ( 2012) Molecular Plant Pathology 13: 414–430; 2. Brown et al., (2010) Fungal Biology 114, 555-571; 3. King et al. (2015) BMC Genomics 16, 544; 4. Brown et al., (2017) Molecular Plant Pathology 18, 1295-1312; 5. Machado et al., (2017) Pest Management Science, doi: 10.1002/ps.4748; 6. Koch et al., 2013, Proc. National Academy of Sciences (USA) 110,19324-9; 7. Cheng et al., 2015, Plant Biotechnology J 13,1335-1345; 8. Urban et al. (2017) Nucleic Acids Research, Database issue 45, D604-D610.
Kim has more than 30 years’ experience in molecular plant pathology and molecular genetics, investigating fungal and viral pathogens of wheat, barley, tomato, potato, oilseed rape and arabidopsis. Since 1998, Kim’s research team has been engaged in the global analysis of newly sequenced genomes of plant infecting fungi. Through this growing interest in large data sets, Kim’s team, in collaboration with computational biologists at Rothamsted Research and the ENSEMBL team (EBI, Cambridge), have established the Pathogen-Host Interactions database (PHI-base) and the interconnected PhytoPath database; their aim is to speed up and refine the exploration of the pathogenic process and host defence. The wheat pathogenomics research is focused on understanding how plant disease resistance mechanisms operate, how fungal pathogens cause disease on wheat crops and on developing novel approaches to evaluate gene function in wheat and fungal pathogens. Specific projects are exploring Host Induced Gene Silencing (HIGS) to control Fusarium infections. Kim’s team has further developed two virus vector systems for the transient over-expression of heterologous proteins in cereal plants to rapidly explore protein function. Take-all root disease research, ongoing at Rothamsted Research since the mid-1920s, is also part of Kim’s research portfolio, which aims to improve global food security.