Modulating glyoxylate cycle intermediates to enhance wheat rust resistance

New sources of resistance against the “polio of agriculture” the wheat rusts are urgently needed due to the threat they pose to wheat production worldwide. Traditionally the most effective means of controlling wheat rust has been the deployment of resistant wheat varieties, through integration of partial or race-specific resistance (R) genes. However, this is a very slow process, and the resistance conferred is frequently overcome through emergence of new pathogen races. An increasingly attractive alternative is to identify and disrupt disease susceptibility genes (S-genes). Plant S-genes are targeted by phytopathogens to promote their growth and infection. Thus, S-gene disruption often confers broad, durable, non-race specific resistance that is very difficult for pathogens to overcome. We recently identified the wheat isocitrate lyase gene (TaICL) as a potential S-gene that when disrupted prevented infection by the wheat yellow rust pathogen (Puccinia striiformis f.sp. tritici, Pst). TaICL disruption led to elevation in glyoxylate cycle intermediates, and we found these compounds can also act exogenously to inhibit Pst infection. The aim of this proposal is to establish how accumulation of the glyoxylate cycle intermediates in TaICL mutant plants prevents Pst infection and also to use this new knowledge to determine the likelihood Pst could overcome these effects. We will specifically resolve whether these compounds are directly toxic to Pst or if they act to indirectly prime defence responses in TaICL disruption mutants. This will be of great value for future exploration of malic and aconitic acid treatment as a method for Pst control, where this analysis will determine whether they should be considered as curative and/or preventative treatments. We will also explore specifically the mechanism(s) altered in Pst that lead to a reduction in infection through TaICL disruption. This new knowledge is critical to determining the longevity of manipulating TaICL as a potential new genetic source of wheat rust resistance. This project is particularly timely as it capitalises on our very recent discovery of TaICL disruption as the first evidence of a genetic avenue for enhancing accumulation of glyoxylate cycle intermediates in crops. The protective benefits of exogenous application and/or enhanced levels of glyoxylate cycle intermediates have also been previously demonstrated in multiple plant species against various pests and pathogens (e.g., wheat powdery mildew, nematodes, brown plant hopper, aphids etc). Thus, we will explore whether disruption of TaICL could also act as a new source of resistance beyond just the wheat rusts. Focusing on establishing if TaICL disruption could be used to enhance wheat’s resilience to three additional critical fungal threats and three major aphid pests in the UK.