Exploiting knowledge of Phytophthora infestans to develop durable late blight disease resistance. Prof Paul Birch

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1 Exploiting knowledge of Phytophthora infestans to develop durable late blight disease resistance Prof Paul Birch To meet projected global food requirements by 2050, the Food and Agriculture Organisation (FAO) of the United Nations estimates that food production will need to increase by 70% overall (and by 100% in developing countries). Currently, 1 billion people are undernourished. A major constraint on achieving food security is crop loss due to pests and diseases; up to 40 50% of crop losses in developing countries are due to these causes. Thus, there is an acute obligation on the science community to find new, durable and sustainable means to combat crop diseases. Potato is the world s third largest food crop. The most serious constraint on its production is the disease late blight, caused by Phytophthora infestans. Globally, this disease costs 4 billion each year, representing a serious threat to food security. Over the past decade we have learned that P. infestans secretes virulence proteins called effectors that are required to suppress the potato innate immune system, allowing this pathogen to cause disease. Some of these effectors are delivered inside living plant cells, where they directly interact with, and manipulate, defence associated host proteins. To combat this, resistance proteins found in wild potato species have evolved to detect the presence of P. infestans effectors. When activated, a resistance protein prevents late blight from occurring. As we learn more about P. infestans effectors (when they are produced; how they are delivered; where they act; what they target) our strategies for combatting late blight are evolving. I will present some of the latest findings that are informing our approaches to developing durable disease resistance.

2 Exploiting knowledge of Phytophthora infestans to develop durable late blight disease resistance Paul Birch Professor of Plant Pathology University of Dundee Most serious potato disease Costing 6.7 billion per year threat to global food security Late Blight - Phytophthora infestans One week later Up to 20 chemical sprays EU directive banning/ reducing chemicals R1 R2 R3 R4 R5 R6 R7 R8 R10 R11 Genetic resistance readily defeated 1

3 P. infestans delivers effector proteins that suppress immunity Avr R Resistance? target Schornack et al AVR3a 1 K 80 I SP RXLR EER Effector domain E 80 M 103 Recognised by potato R3a Armstrong et al (2005) PNAS 102: Co-expression of Avr3a and R3a in N. benthamiana Rehmany et al (2005) Plant Cell 17: Birch et al (2006) Trends Microbiol 14:8-11 RXLR required for translocation 464 RXLR-EERs predicted in P. infestans Whisson et al (2007) Nature 450: All AVR proteins are RXLRs Armstrong et al (2005) PNAS 102: Bos et al. (2006) Plant J. 48:

4 How can we improve resistance? 60 effectors identified as high priority Expressed in different genotypes Some essential (RNAi and stable silencing) RXLRcontrol Steve Whisson, Anna Avrova, Zhendong Tian, Sonia Gomez Effectors: what do they target to disable immunity? Can we prevent this? Resistance proteins: can we find or make R genes that are more durable? Avr3a suppresses INF1 cell death K I SP RxLR EER Effector domain 80 E M 80 INF1 PAMP Y X INF1 cell death suppression How does it suppress INF1 cell death? Bos et al 2006;

5 AVR3a interacts with host E3 ligase CMPG1 in yeast and in planta CMPG1 is required for INF1-triggered cell death (Gonzalez-Lamothe et al 2006) AVR3a inhibits CMPG1 AVR3a Y147-del mutant doesn t interact with CMPG1 or inhibit it (2010) 107: Essential? Stable silencing of AVR3a Complementation EM Y147 EM Y147 Non-silenced Silenced KI Y147 KI Y147 AVR3a is essential for infection. Steve Whisson, Tian Zhendong, Ingo Hein, Ramesh Vetukuri 4

6 CBEL INF1 Avr9/Avr4 Rec. CBEL?? BAK1 Rec. INF1 Cf9/ CF4 Pto Prf Plasma membrane recognition events AvrPto T3SS Pst HR CMPG1 Q: can we modify CMPG1 so no longer interacting with AVR3a, whilst retaining its function? Intracellular effectors recognised by cytoplasmic NBS-LRR proteins (2011) New Phytol 190: How can we find, or make, durable disease resistance? 5

7 Natural sources of resistances Commonwealth Potato Collection (CPC) started in 1938 & 1939 with collecting expeditions to Mexico and S. America. now >1800 accessions, >80 species. Feeds germplasm into the potato breeding programme at JHI Looking for durable resistance knowing RXLRs Are all RXLR genes expressed? Are they essential for infection? How diverse are they in P. infestans populations? Take selected RXLRs to screen the CPC AVR3a to demonstrate: Expression in all genotypes Silencing essential for disease Diversity? 6

8 P. infestans AVR3a genotypes in the Toluca Valley, Mexico K 80 I 103 Q/H 133 M/L Y SP RxLR EER AVR3a E 80 M 103 R/G 124 Q/H 133 Miles Armstrong Avr3a EM dominates in Mexican populations. Recognition of Avr3a EM and KI by resistant CPC accessions S. sem 7103 x Cara IH09.14 pop IH09.14/12 x IH10_29 How can we clone resistance genes more rapidly? 7

9 Whole genome analysis how many NB LRRs are there? NB-LRR genes 266 NB/TIR genes NGS based methods to more rapidly map and clone R genes NB-LRR-enrichment: 2-3 NB-LRR exon Potato, Tomato, known Pepper NB-LRRs probes (120 nt) (Agilent SureSelect) >500-fold enrichment of R genes Florian Jupe, Walter Verweij, Kamil Witek, Jonathan Jones (TSL) 8

10 R3 locus on chromosome 11: high read depth identifies six new NB-LRRs Read depth Previously identified R genes Newly identified R genes Plant J on-line 704 NB-LRR R genes in potato RenSeq being used on R and S bulks of populations segregating late blight resistance Engineering novel resistances - Example R3a R3a *1 &EM R3a_wt&EM R3a *1 &KI R3a_wt&KI R3a *1 Sean Chapman, Xinwei Chen, Laura Stevens 9

11 Provide resistance to AVR3a EM homozygote R3a *1 R3a *2 R3a *1 R3a *2 R3a *3 R3a WT R3a *3 R3a WT Conclusion: Knowledge of P. infestans effector function and importance can drive our quest for durable late blight resistance Collaborators: Beynon Group (Warwick) Kamoun, JJ Groups (Sainsbury Lab) Dave Cooke, Ingo Hein, Pete Hedley, Sean Chapman (JHI) Huitema Group (UoDundee) Frederic Brunner (Tuebingen) Vleeshouwers Group (Wageningen) 10

12 Thank you 11