Novel players of the cell wall integrity sensing pathway controlled by the ANXUR Receptor-like kinases.
Final Report Abstract
Tip-growing cells in plants, such as root hairs and pollen tubes, are among the fastest growing cells in the eukaryotic kingdom. To reach such speed, they play the dangerous game of locally loosening/deforming their rigid yet dynamic extracellular cell wall (CW) enough to allow expansion but not too much as to maintain their integrity. Tip-growing cells have thus developed very robust CW integrity (CWI) maintenance mechanisms to relay information about CW performance to the internal growth machinery so as to avoid integrity loss. Part of this CWI maintenance is governed by the malectin-like receptor kinases FERONIA (FER) and its closest homologues ANXUR1 (ANX1) and ANX2 that controls CWI in root hairs and pollen tubes, respectively. T-DNA insertional mutants in FER display bursting root hairs while double mutants in both ANX1 and ANX2 exhibit pollen tubes that burst precociously preventing them from fertilizing female gametophytes and thereby leading to sterility. To identify new players of this largely unexplored pathways, an anx1 anx2 sterility suppressor screen was performed and led to the identification of suppressors with improved fertility due to rescue of anx1 anx2 pollen tube growth. For our first two suppressors, mapping by next-generation sequencing identified non-synonymous mutations in key functional domains of a receptor-like cytoplasmic kinase (RLCK) and a Ser/Thr phosphoprotein phosphatase (PPP), respectively. Both the RLCK and the PPP are expressed in pollen and root tissues and were named MARIS (MRI) and ATUNIS1 (AUN1) according to Etruscan deities of fertility and rebirth, respectively. Interestingly, we could show on one hand that the plasma membrane localized MRI functions as a positive component of the CWI pathways downstream of ANX1/2 in pollen tubes and FER in root hairs. On the other hand, the nucleocytoplasmic AUN1 and its closest homologue AUN2 together promote tip-growth and negatively regulate CWI maintenance of tip-growing cells. Furthermore, the suppressor screen led to the identification of both a dominant hypermorph variant of MRI (MRIR240C), and a dominant hypomorph variant of AUN1 (AUN1D94N), that were instrumental in testing genetic interactions with recently identified regulators of CWI. Surprisingly, MRI and AUN1/2 appear to define two independent but converging pathways to fine-tune CWI during tip-growth. To further understand the growth control exerted by the CWI pathways in plants, one major step forward will be identifying the direct targets of phosphorylation and dephosphorylation of these protein kinases and phosphatases, respectively.
Publications
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(2015). The receptor-like cytoplasmic kinase MARIS functions downstream of CrRLK1L-dependent signaling during tip growth. PNAS 112:12211-6
Boisson-Dernier, Aurélien; Franck, Christina Maria; Lituiev, Dmytro S. & Grossniklaus, Ueli
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(2017). Imaging Ca2+ dynamics in wild-type and NADPH oxidase-deficient mutant pollen tubes with Yellow Cameleon and confocal laser scanning microscopy. Methods in Mol. Biol. 1669:103-116
Franck, Christina Maria; Westermann, Jens & Boisson-Dernier, Aurélien
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(2017). RALF4/19 peptides interact with LRX proteins to control pollen tube growth in Arabidopsis. Science 358:1600-1603
Mecchia, Martin A.; Santos-Fernandez, Gorka; Duss, Nadine N.; Somoza, Sofía C.; Boisson-Dernier, Aurélien; Gagliardini, Valeria; Martínez-Bernardini, Andrea; Fabrice, Tohnyui Ndinyanka; Ringli, Christoph; Muschietti, Jorge P. & Grossniklaus, Ueli
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(2018). Plant Malectin-Like Receptor Kinases: From Cell Wall Integrity to Immunity and Beyond. Annu. Rev. Plant Biol. 69:301-328
Franck, Christina Maria; Westermann, Jens & Boisson-Dernier, Aurélien
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(2018). The protein phosphatases ATUNIS1 and ATUNIS2 regulate cell wall integrity in tip-growing cells. Plant Cell 30:1906-1923
Franck, Christina Maria; Westermann, Jens; Bürssner, Simon; Lentz, Roswitha; Lituiev, Dmytro Sergiiovych & Boisson-Dernier, Aurélien
