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Published on December 27, 2007; 10.1104/pp.107.112995

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Received November 9, 2007
Accepted December 17, 2007

Specificity of RCN1-mediated protein phosphatase 2A regulation in meristem organization and stress response in roots

Joshua J. Blakeslee , Hong-Wei Zhou , Jeffrey T. Heath , Kyle R. Skottke , Jorge A. Rodriguez Barrios , Su-Yang Liu , and Alison DeLong *

Department of Molecular Biology, Cell Biology and Biochemistry, Brown University, Providence RI

* Corresponding author; email: Alison_DeLong{at}Brown.edu.

Protein dephosphorylation by the serine/threonine protein phosphatase 2A (PP2A) modulates a broad array of cellular functions. PP2A normally acts as a heterotrimeric holoenzyme complex comprising a catalytic subunit bound by regulatory A and B subunits. Characterization of the regulatory A subunit isoforms (ROOTS CURL IN NAPHTHYLPHTHALAMIC ACID1 [RCN1], PP2AA2 and PP2AA3) of Arabidopsis thaliana PP2A has shown that RCN1 plays a primary role in controlling root and hypocotyl PP2A activity in seedlings. Here we show that hypocotyl and root growth exhibit different requirements for RCN1-mediated regulation of protein phosphatase 2A activity. Roots of rcn1 mutant seedlings exhibit characteristic abnormalities in cell division patterns at the root apical meristem, as well as reduced growth under ionic, osmotic and oxidative stress conditions. We constructed chimeric A subunit genes and found that restoration of normal root tip development in rcn1 plants requires both regulatory and coding sequences of RCN1, while the hypocotyl elongation defect of rcn1 plants can be complemented by either RCN1 or PP2AA3 transgenes. Furthermore, the RCN1 and PP2AA3 proteins exhibit ubiquitous subcellular localization patterns in seedlings and both associate with membrane compartments. Together, these results show that RCN1-containing PP2A has unique functions that cannot be attributed to isoform-specific expression and localization patterns. Post-embryonic RCN1 function is required to maintain normal auxin distribution and stem cell function at the root apex. Our data show that RCN1-regulated phosphatase activity plays a unique role in regulating post-embryonic root development and stress response.






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