The C2-domain protein QUIRKY and the receptor-like kinase STRUBBELIG localize to plasmodesmata and mediate tissue morphogenesis in Arabidopsis thaliana

Vaddepalli P, Herrmann A, Fulton L, Oelschner M, Hillmer S, Stratil TF, Fastner A, Hammes UZ, Ott T, Robinson DG, Schneitz K

Abstract
Tissue morphogenesis in plants requires communication between cells. This process involves trafficking of molecules through plasmodesmata (PD). PD conductivity is regulated by endogenous and exogenous signals; however, the underlying signaling mechanisms remain enigmatic. In Arabidopsis, signal transduction mediated by the receptor-like kinase STRUBBELIG (SUB) contributes to inter-cell-layer signaling during tissue morphogenesis. Previous analysis revealed that SUB acts non-cell-autonomously suggesting that SUB controls tissue morphogenesis by participating in the formation or propagation of a downstream mobile signal. A genetic screen identified QUIRKY (QKY), encoding a predicted membrane-anchored C2-domain protein, as a component of SUB signaling. Here, we provide further insight into the role of QKY in this process. We show that similar to SUB, QKY exhibits non-cell-autonomy when expressed in a tissue-specific manner and non-autonomy of QKY extends across several cells. In addition, we report localization studies revealing that QKY and SUB co-localize to PD and that co-localization occurs independently from each other. Using FRET-FLIM analysis we show that SUB and QKY can form a heteromeric complex at PD in vivo. We propose a model where SUB and QKY interact at PD to promote PD conductivity thereby linking RLK-dependent signal transduction and inter-cellular communication mediated by PD.