ARABIDOPSIS CRINKLY4 Function, Internalization, and Turnover Are Dependent on the Extracellular Crinkly Repeat Domain

Abstract

The study of the regulation and cellular dynamics of receptor kinase signaling in plants is a rapidly evolving field that promises to give enormous insights into the molecular control of signal perception. In this study, we have analyzed the behavior of the L1-specific receptor kinase ARABIDOPSIS CRINKLY4 (ACR4) from Arabidopsis thaliana in planta and have shown it to be present in two distinct compartments within cells. These represent protein export bodies and a population of internalized vesicles. In parallel, deletion analysis has shown that a predicted b-propeller-forming extracellular domain is necessary for ACR4 function. Nonfunctional ACR4 variants with deletions or point mutations in this domain behave differently to wild-type fusion protein in that they are not internalized to the same extent. In addition, in contrast with functional ACR4, which appears to be rapidly turned over, they are stabilized. Thus, for ACR4, internalization and turnover are linked and depend on functionality, suggesting that ACR4 signaling may be subject to damping down via internalization and degradation. The observed rapid turnover of ACR4 sets it apart from other recently studied plant receptor kinases. Finally, ACR4 kinase activity is not required for protein function, leading us to propose, by analogy to animal systems, that ACR4 may hetero-oligomerize with a kinase-active partner during signaling. Plant and animal receptor kinases have distinct evolutionary origins. However, with other recent work, our study suggests that there has been considerable convergent evolution between mechanisms used to regulate their activity.

Surface Position, Not Signaling from Surrounding Maternal Tissues, Specifies Aleurone Epidermal Cell Fate in Maize

“…One possible mechanism for this is that positive signaling for aleurone cell fate specification occurs by membrane proteins that are ubiquitously distributed, but only active (uninhibited) in surface membranes of endosperm surface cells. Although the molecules responsible for the proposed signaling are yet to be identified, Cr4 and Dek1 are attractive candidates, both proteins being predicted to be located in plasma membranes and both having extracellular domains capable of mediating cell-to-cell interactions (Becraft et al, 1996;Lid et al, 2002;Gifford et al, 2005). Additional observations that make Dek1 an attractive candidate for a direct role in aleurone cell fate specification is that it acts cell autonomously; starchy endosperm cells that lack Dek1 are unable to respond to surface position by converting to the aleurone cell fate (Becraft and Asuncion-Crabb, 2000).…”

“…Recently, Cr4 and Dek1 have also been implicated in epidermal cell fate specification in different organs of Arabidopsis (Arabidopsis thaliana) and tobacco (Nicotiana tabacum; Johnson and Russell, 1982;Tanaka et al, 2002;Gifford et al, 2003Gifford et al, , 2005Ahn et al, 2004;Cao et al, 2005;Lid et al, 2005). It therefore appears likely that epidermal cell fate specification in plants, including aleurone cells, occurs through a process that is conserved among all organs and between monocots and dicots.…”

The Cytokinin Receptors of Arabidopsis Are Located Mainly to the Endoplasmic Reticulum

“…However, attempts to demonstrate an influence of cytokinin or the inhibitor of endosomal recycling brefeldin A on the localization of cytokinin receptor-GFP fusion proteins have not been successful so far (Wulfetange, 2010). Thus, a model involving the recycling of the receptors between the ER and the PM, as has been described for BRI1 and the receptor-like kinase CRINKLY4 (Gifford et al, 2005;Geldner et al, 2007), is currently not supported experimentally for the cytokinin receptors.…”

The Plant Defense Elicitor Cryptogein Stimulates Clathrin-Mediated Endocytosis Correlated with Reactive Oxygen Species Production in Bright Yellow-2 Tobacco Cells

“…This has been indirectly established for the tomato (Lycopersicon esculentum) LeEiX2 receptor of the fungal ethylene-inducing xylanase elicitor, which contains a Tyr-based motif functioning as an endocytotic signal (Ron and Avni, 2004). Moreover, some receptor-like kinases are localized in an FM4-64 positive compartment (Gifford et al, 2005), sometimes complexed with their ligand (Shah et al, 2002;Russinova et al, 2004), although these receptors undergo constitutive internalization. The cryptogein receptor has not been identified yet, but preliminary observations of colloidal gold-labeled cryptogein inside BY-2 cells 5 min after elicitor treatment suggest that the cryptogein receptor follows a similar route (J. Lherminier, unpublished data).…”

“…However, plasma membrane receptor-ligand interactions are frequently incompletely characterized. The involvement of endocytotic processes of receptors for signal transduction during plant development has been discovered only recently (Shah et al, 2002;Russinova et al, 2004;Gifford et al, 2005;Kwaaitaal et al, 2005). Shah et al (2002) suggested that only cells showing endocytosis of the receptors are actively engaged in ligand-mediated signaling.…”