Novel players of the cell wall integrity sensing pathway controlled by the ANXUR Receptor-like kinases.

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Plant cells are directing the synthesis/deposition of an extracellular matrix rigid yet dynamic known as the cell wall (CW) that fulfils various key functions during development. The cells synthesize primary CWs during growth, which depends on the balance between loosening/deformation of the pre-existing CW and continuous secretion of new material. This essential coordination requires the cell to be informed of any environmental perturbations that impact its CW properties so as to avoid growth arrest or rupture. To circumvent these catastrophic scenarios, it has become increasingly evident that plant cells have developed CW integrity (CWI) sensing mechanisms to relay information about CW performance to the internal growth machinery. Despite its importance in plant development and growth, our understanding of the signalling mechanisms between the CW and the intracellular machineries remains however meagre.The receptor-like kinases (RLKs) of the Catharanthus roseus RLK1-like (CrRLK1L) family have recently emerged as candidates for coordinating cell growth, cell-cell communication, and CW remodelling during development (Lindner, et al., 2012). Interestingly, two redundant CrRLK1L members named ANXUR1 (ANX1) and ANX2 function in the control of CW integrity (CWI) in pollen tubes (PTs), the male gametophyte of flowering plants. Pollen carrying mutations in both receptors burst shortly after germination, preventing them from fertilizing female gametophytes thereby leading to sterility (Boisson-Dernier, et al., 2009). Recently, ANX-RLKs were shown to regulate H2O2 production, Ca2+ homeostasis and secretion through NADPH oxidases to achieve steady growth without losing integrity (Boisson-Dernier, et al., 2013).To identify new players of this largely unexplored pathway, a anx1;anx2 sterility suppressor screen was performed and led to the identification of suppressors with improved fertility due to rescue of anx1;anx2 PT growth. For our first two suppressors, mapping by next-generation sequencing identified non-synonymous mutations in key functional domains of a novel receptor-like cytoplasmic kinase (RLCK) and a protein Ser/Thr phosphatase (PPP), respectively. Both the RLCK and the PPP are pollen-preferentially expressed and were named MARIS (MRI) and ATUNIS1 (AUN1) according to Etruscan deities of fertility and rebirth, respectively. Through an interdisciplinary proposal that includes state-of-the-art techniques in molecular and cell biology, genetics and biochemistry we propose to unravel the role of MRI and AUN1 in the ANX-RLK dependent CWI sensing pathway.