BacCORAC: Bacterial modulation of plant responses via CORonafacic Acid Conjugates

Potato, the world’s third main food crop, is produced in over 100 countries and is a critical crop in terms of food security in the face of increasing populations and hunger rates. Potato food security is challenged by multiple pests and pathogens compounded with climate change and the need for sustainable agri-chemical solutions to improve crop resilience. To find potential solutions, research into the actions of natural biological products is fundamental. Plant development and health is partly controlled by a complex regulatory network and cross-talk of phytohormones including auxins, gibberellins, ethylene, salicylic acid and jasmonates. This cross-talk can be influenced by bacteria, both beneficial and pathogenic, colonising the plant through hormone mimicry, sequestration or degradation. Secondary metabolites produced from microbes offer a natural resource for future agri-chemical products and many biosynthetic gene clusters (BGCs) remain to be fully understood across different bacterial species. Distantly related plant or soil-associated bacterial species encode the BGC for coronafacic acid (CFA), which has phytotoxic properties when joined to amino acids or their derivatives, such as coronamic acid (CMA). The first discovered and most characterised such phytotoxin is coronatine (COR; CFA+CMA). COR acts as a potent jasmonate mimic modulating downstream plant responses, such as plant immunity and root growth. The potato pathogen Pectobacterium atrosepticum produce CFA, but cannot produce CMA, resulting in amino acids valine/isoleucine being joined to CFA instead (hereby called CFA-conjugates). COR’s strong effects on the jasmonate signalling pathways have been well characterised in the model plant Arabidopsis, but less is known about the responses to CFA-conjugate mimics, and little is known about such responses in major crops such as potato. The project will focus on the phytopathogen P. atrosepticum (Pba) which causes blackleg and tuber soft rot of potato, with no chemical methods of control. To date, only Pectobacterium strains that are restricted to cause disease symptoms on potato can produce CFA-conjugates. Our preliminary results show that Pba produce mainly CFA-valine and Pba CFA knock-out mutants are reduced in plant root colonisation, root growth inhibition and disease progression. The aim of the project is to understand the regulation of CFA production in Pba and the biological role of CFA conjugates in potato-Pba interactions. Our approach will be across three work-packages to: Elucidate the regulation of CFA expression in Pba. Identify plant proteins that bind to CFA-valine/isoleucine conjugates. Identify potato genes that are affected by the presence of CFA- conjugates. COR has been studied for multiple agri-chem applications, including as a weedkiller (herbicide) or promoting plant resistance to drought-stress or insect-feeding. Jasmonates and COR have been shown to promote potato tuber initiation and expansion. Understanding the function of CFA-valine/isoleucine in Pba-potato interactions could inform on potential points of intervention to control potato infection or disease progression. Fundamental insights into CFA-conjugates modulating potato responses can lead to innovative ways to improve potato plant growth and tolerance to stresses. This interdisciplinary project fits well within the BBSRC strategic plan for sustainable agriculture and food linking to the spotlight area of ’developing novel crop protection strategies’. Although this project focusses on the Pba-potato pathosystem, the outcomes from the project will inform on other important plant pathogens which produce CFA-AA, such as Brenneria spp (causes Acute Oak Decline) or Pseudomonas spp (infects broad range of plants).