Structural basis of Joka2-mediated autophagy in plant immunity.

The increasing global population together with the reduction in crop yield has brought upon challenges in food security (1,2). A main effector of this are rapidly evolving plant pathogens (3). Due to their immobility, plants must defend themselves against invading pathogens. Plants rely on individual cells innate immunity to defend themselves and autophagy has been described as a major contributor (4,5). The plant homolog of mammalian p62 and Arabidopsis thaliana NBR1 autophagy cargo receptors, Joka2, has been shown to mediate destruction of protein aggregates and viral proteins (Figure 1). On the other hand, Joka2 has been implicated in promoting plant protection against bacteria and oomycete pathogens (6,7). In turn, the Irish potato famine pathogen Phytophthora infestans subverts defense-related autophagy by secreting a virulence factor, known as PexRD54, that depletes Joka2 out of the autophagy machinery via interacting with ATG8 (8). How Joka2 contributes to innate immunity through autophagy and its cargo selectivity remain unknown. Details of Joka2's molecular architecture are based on homologs p62 and NBR1. This project aims to reveal functional and structural properties of defence-related autophagy regulated by the autophagy cargo receptor Joka2. We will utilise a combination of techniques involving the biophysical technique surface plasmon resonance, imaging technique confocal fluorescence microscopy, in planta assays to measure immune response and structural techniques X-ray crystallography and cryo electron microscopy. We hope this interdisciplinary approach will reveal the manner Joka2 contributes to immunity but specifically how it is arranged in the cell, in terms of oligomerization, where it is localised during an infection and how and the biochemistry of individual domains contributing to function. We will utilise structure-based mutagenesis to provide physiological relevance.

References
1. Hodson, R. (2017). Food security. Nature, 544(7651), pp.S5-S5.
2. Popp, J., Peto, K. and Nagy, J. (2013) 'Pesticide productivity and food security. A review', Agronomy for Sustainable Development, 33(1), pp. 243-255.
3. Liu, T., Song, T., Zhang, X., Yuan, H., Su, L., Li, W., Xu, J., Liu, S., Chen, L., Chen, T., Zhang, M., Gu, L., Zhang, B. and Dou, D. (2014). Unconventionally secreted effectors of two filamentous pathogens target plant salicylate biosynthesis. Nature Communications, 5(1).
4. Chaparro-Garcia, A., Schwizer, S., Sklenar, J., Yoshida, K., Petre, B., Bos, J. I. B., Schornack, S., Jones, A. M. E., Bozkurt, T. O. and Kamoun, S. (2015) 'Phytophthora infestans RXLR-WY Effector AVR3a Associates with Dynamin-Related Protein 2 Required for Endocytosis of the Plant Pattern Recognition Receptor FLS2', Plos One, 10(9), pp. 27.
5. Dangl, J. L. and Jones, J. D. G. (2001) 'Plant pathogens and integrated defence responses to infection', Nature, 411(6839), pp. 826-833.
6. Zientara-Rytter, K., Lukomska, J., Moniuszko, G., Gwozdecki, R., Surowiecki, P., Lewandowska, M., Liszewska, F., Wawrzynska, A. and Sirko, A. (2011). Identification and functional analysis of Joka2, a tobacco member of the family of selective autophagy cargo receptors. Autophagy, 7(10), pp.1145-1158.
7. Zientara-Rytter, K. and Sirko, A. (2014). Significant role of PB1 and UBA domains in multimerization of Joka2, a selective autophagy cargo receptor from tobacco. Frontiers in Plant Science, 5.
8. Dagdas, Y. F., Belhaj, K., Maqbool, A., Chaparro-Garcia, A., Pandey, P., Petre, B., Tabassum, N., Cruz-Mireles, N., Hughes, R. K., Sklenar, J., Win, J., Menke, F., Findlay, K., Banfield, M. J., Kamoun, S. and Bozkurt, T. O. (2016) 'An effector of the Irish potato famine pathogen antagonizes a host autophagy cargo receptor', Elife, 5, pp. 23.