Réf ABG-125661

Sujet de Thèse

04/09/2024

Autre financement public

Clermont-Ferrand - Auvergne-Rhône-Alpes - France

Exploring gene diversity in wheat-Zymoseptoria tritici interactions as a path to improved Septoria tritici blotch control

• Biologie

Septoria tritici blotch (STB), caused by the fungal pathogen Zymoseptoria tritici, is one of the most devastating diseases in France and Europe. This pathogen induces leaf necrosis, reducing photosynthesis and yield by an average of 1.5 tons per hectare per year. In the current agro-ecological context, sustainable management of STB primarily involves implementing integrated pest management (IPM) strategies, with the use of resistant wheat cultivars as the main pillar.

To date, 23 Stb genes and over 300 QTL conferring resistance to Z. tritici have been mapped on the wheat genome. Three Stb genes - Stb6, Stb15, and Stb16q - have been cloned. These genes encode receptor-like protein kinases anchored at the plasma membrane, which detect the presence of the pathogen extracellularly. In the early 2000s, it was shown that resistance mediated by the Stb6 gene follows a gene-for-gene interaction with the corresponding avirulence gene from Z. tritici, Avr Stb6. More recently, similar interactions have been observed for other Stb/Avr Stb genes, raising questions about the universality of this interaction model. On the pathogen side, four Avr Stb genes have been cloned: Avr3D1, Avr Stb6, Avr Stb9, and Avr Stb20q. The exact mechanism (direct or indirect) by which Avr Stb proteins are recognized by Stb proteins is currently unknown. A wide number of haplotypes has already been described for these Avr Stb genes that mediate varying efficiencies of resistance against the same Stb alleles. On the other side, genetic diversity on Stb genes has been revealed with for instance 22 different alleles of Stb6 described in the literature but only one known to confer resistance. While the impact of Avr Stb diversity on the outcome of the interaction has been investigated, the effect of diversity of Stb alleles has not been as thoroughly studied, limiting the available alleles for breeding resistant cultivars and understanding the Stb/Avr Stb recognition.

The population of Z. tritici is genetically very diverse, with several million haplotypes per hectare of wheat. This pathogen undergoes several cycles of sexual reproduction per year, allowing it to evolve rapidly and potentially overcome resistant wheat cultivars. To mitigate this, one proposed strategy is to diversify resistances and deploy them with a faster turnover based on the frequency of corresponding avirulence genes in the natural fungal population. This strategy requires a thorough understanding of the diversity of Stb/Avr Stb interactions, the mechanisms of recognition between wheat and Z. tritici, and comprehensive data on the number, distribution, and frequency of Avr Stb genes in the natural population of Z. tritici. To this end, the Ph D project will be divided in two main objectives: