Growth-inhibiting effects of the unconventional plant APYRASE 7 of Arabidopsis thaliana influences the LRX/RALF/FER growth regulatory module.

Plant cell growth involves coordination of numerous processes and signaling cascades among the different cellular compartments to concomitantly enlarge the protoplast and the surrounding cell wall. The cell wall integrity-sensing process involves the extracellular LRX (LRR-Extensin) proteins that bind RALF (Rapid ALkalinization Factor) peptide hormones and, in vegetative tissues, interact with the transmembrane receptor kinase FERONIA (FER). This LRX/RALF/FER signaling module influences cell wall composition and regulates cell growth. The numerous proteins involved in or influenced by this module are beginning to be characterized. In a genetic screen, mutations in Apyrase 7 (APY7) were identified to suppress growth defects observed in lrx1 and fer mutants. APY7 encodes a Golgi-localized NTP-diphosphohydrolase, but opposed to other apyrases of Arabidopsis, APY7 revealed to be a negative regulator of cell growth. APY7 modulates the growth-inhibiting effect of RALF1, influences the cell wall architecture and -composition, and alters the pH of the extracellular matrix, all of which affect cell growth. Together, this study reveals a function of APY7 in cell wall formation and cell growth that is connected to growth processes influenced by the LRX/RALF/FER signaling module. Author summary: The upright posture of land plants is made possible by solid walls that surround each individual cell. Hence, plant cell growth requires coordinated processes that expand the cell and, spatially and temporally controlled, the surrounding cell wall. On the molecular level, proteins involved in cell wall integrity (CWI) sensing monitor the status of the cell wall and influence and coordinate growth processes. Mutations in the genes encoding proteins of the CWI sensing machinery interfere with controlled cell growth, resulting in cells that are malformed, too small or big, or, as in root hairs, that even burst. In Arabidopsis, we found that the bursting of root hairs can be alleviated by changing a protein of the Golgi apparatus, APYRASE7. APYRASE7 appears to be a downstream target of the CWI sensing system since mutating the APYRASE7 gene has an impact on the CWI sensing machinery, on cell growth, and the response to a peptide hormone regulating cell growth. Thus, our work provides a better insight into the different proteins involved in and necessary for controlled cell (wall) growth to take place. [ABSTRACT FROM AUTHOR]

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