Abstract - The interaction of C-TERMINALLY ENCODED PEPTIDEs (CEPs) with CEP RECEPTOR1 (CEPR1) controls root growth and development, as well as nitrate uptake, but the underlying protein interactions involved are yet to be comprehensively defined.

Here I describe extensive genetic evidence demonstrating that SOMATIC-EMBRYOGENESIS RECEPTOR-LIKE KINASEs (SERKs) function redundantly to help regulate CEP-CEPR1 control of primary and lateral root growth, as well as downstream transcriptional targets. CEPR1 interacted in a ligand-independent manner with several SERKs when transiently co-expressed in Nicotiana benthamiana. Using complementary genetic and biochemical approaches, I established that SERKs, as co-receptors, play essential roles in the CEP-mediated signalling pathway.

In an untargeted proteomic approach to identify novel interaction partners, several CEPR1-associated proteins were identified, including the Arabidopsis sucrose transporter SUC2. The relationship between CEPR1 and SUC2 was characterised in two heterologous expression systems, Nicotiana benthamiana and Xenopus laevis oocytes. Reciprocal co-immunoprecipitations of CEPR1-CITRINE and SUC2-HA3 expressed in Nicotiana benthamiana leaves provided independent validation of a CEPR1-SUC2 interaction. Heterologous expression of CEPR1 and SUC2 in Xenopus laevis oocytes was used to demonstrate that CEPR1 promotes SUC2-mediated sucrose uptake, and that this is inhibited by CEPs. Together, these results suggest a novel role for CEP-CEPR1 signalling in controlling sucrose allocation by regulating SUC2-mediated loading of photosynthetic sugars into the phloem.

Biography - Katia is a PhD student in the Djordjevic Lab, Research School of Biology, ANU. She carried out her PhD jointly between ANU and the Grossniklaus Lab at the University of Zurich. Prior to her PhD, she completed a Bachelor of Science (Honours) at ANU.