Mutation of a Conserved Motif of PP2C.D Phosphatases Confers SAUR Immunity and Constitutive Activity1[OPEN]
Single missense mutations in a conserved motif of PP2C.D proteins abolish SAUR binding, leading to constitutive phosphatase activity that restricts cell expansion. The phytohormone auxin promotes the growth of plant shoots by stimulating cell expansion via plasma membrane (PM) H + -ATPase activation...
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Published in | Plant physiology (Bethesda) Vol. 181; no. 1; pp. 353 - 366 |
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Main Authors | , , , , |
Format | Journal Article |
Language | English |
Published |
American Society of Plant Biologists
16.07.2019
|
Online Access | Get full text |
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Summary: | Single missense mutations in a conserved motif of PP2C.D proteins abolish SAUR binding, leading to constitutive phosphatase activity that restricts cell expansion.
The phytohormone auxin promotes the growth of plant shoots by stimulating cell expansion via plasma membrane (PM) H
+
-ATPase activation, which facilitates cell wall loosening and solute uptake. Mechanistic insight was recently obtained by demonstrating that auxin-induced SMALL AUXIN UP RNA (SAUR) proteins inhibit D-CLADE TYPE 2C PROTEIN PHOSPHATASE (PP2C.D) activity, thereby trapping PM H
+
-ATPases in the phosphorylated, activated state, but how SAURs bind PP2C.D proteins and inhibit their activity is unknown. Here, we identified a highly conserved motif near the C-terminal region of the PP2C.D catalytic domain that is required for SAUR binding in Arabidopsis (
Arabidopsis thaliana
). Missense mutations in this motif abolished SAUR binding but had no apparent effect on catalytic activity. Consequently, mutant PP2C.D proteins that could not bind SAURs exhibited constitutive activity, as they were immune to SAUR inhibition. In planta expression of SAUR-immune
pp2c.d2
or
pp2c.d5
derivatives conferred severe cell expansion defects and corresponding constitutively low levels of PM H
+
-ATPase phosphorylation. These growth defects were not alleviated by either auxin treatment or 35S:StrepII-SAUR19 coexpression. In contrast, a PM H
+
-ATPase gain-of-function mutation that results in a constitutively active H
+
pump partially suppressed SAUR-immune
pp2c.d5
phenotypes, demonstrating that impaired PM H
+
-ATPase function is largely responsible for the reduced growth of the SAUR-immune
pp2c.d5
mutant. Together, these findings provide crucial genetic support for SAUR-PP2C.D regulation of cell expansion via modulation of PM H
+
-ATPase activity. Furthermore, SAUR-immune
pp2c.d
derivatives provide new genetic tools for elucidating SAUR and PP2C.D functions and manipulating plant organ growth. |
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Bibliography: | www.plantphysiol.org/cgi/doi/10.1104/pp.19.00496 W.M.G., J.H.W., and A.K.S. designed the research; J.H.W., A.K.S., M.Y.P., and M.D. performed the experiments; W.M.G. supervised the experiments; J.H.W. and W.M.G. wrote the article with contributions from all authors. The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: William M. Gray (grayx051@umn.edu). These authors contributed equally to the article. Senior author. |
ISSN: | 0032-0889 1532-2548 |
DOI: | 10.1104/pp.19.00496 |